ON
DIGESTION
AND
DIETETICS.
THE
PHYSIOLOGY OF DIGESTION
CONSIDERED WITH RELATION TO
THE PRINCIPLES OF DIETETICS.
BY ANDREW COMBE, M. D.
FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS IN EDINBURGH,
AND
CONSULTING PHYSICIAN TO THEIR MAJESTIES THE KING AND QUEEN
OF THE BELGIANS.
SECOND EDITION
REVISED AND ENLARGED.
“Nor is it left _arbitrary_, at the will and pleasure of every
man, to do as he _list_; after the dictates of a depraved
_humour_ and extravagant _phancy_, to live at what rate he
pleaseth; but every one is bound to observe the _Injunctions_
and _Law of Nature_, upon the penalty of forfeiting their
_health_, _strength_, and _liberty_,--the true and long
enjoyment of themselves.”
MAINWAYRINGE.
EDINBURGH:
MACLACHLAN & STEWART;
AND SIMPKIN, MARSHALL & CO. LONDON.
MDCCCXXXVI.
PRINTED BY NEILL & CO. OLD FISHMARKET.
ADVERTISEMENT
TO THE
SECOND EDITION.
The first edition of the present volume consisted of 2000 copies, and
has been exhausted in little more than five months. Already, also,
it has been twice reprinted in the United States. This success is
extremely gratifying, and shews that the desire for information on the
subject of the human constitution, is rapidly extending in proportion
as it is discovered to be perfectly within the comprehension of every
ordinary capacity, and to be directly and easily applicable to the
farther improvement of the moral and physical condition of man.
The edition now offered to the public has been carefully revised,
and about twenty pages of new matter have been added. Still, I fear,
that many imperfections remain, which leisure and more confirmed
health might have enabled me to remove, but which, under present
circumstances, I feel compelled to leave to the good-natured indulgence
of the reader.
It has been suggested by a professional critic for whose judgment
I feel the utmost deference, that “the work would really have been
more useful if the physiological or introductory part had been
more condensed;” as much of it will, he thinks, be neither readily
comprehended, nor usefully retained by the _general_ reader.[1]
My only reason for not acting on this suggestion is, that I regard the
exposition of the laws of digestion of which that part consists, as
the foundation on which all the dietetic rules contained in the second
part must necessarily rest,--and am therefore extremely anxious that
their nature and mode of operation should be thoroughly understood
by the ordinary reader, even at the risk of too great minuteness. I
am quite aware that the detail into which I have entered must appear
tedious to every well educated practitioner; but as the book was
intended more for the general than for the medical reader, the latter
is evidently a less competent judge in this particular matter than
the former. On referring, accordingly, to an _unprofessional_
critic of no small ability and reputation, we find him of an entirely
opposite opinion. For--“Of the two divisions of the book,” he thinks,
“the FIRST is the most satisfactory and interesting, from
the nature of its subject and the popular novelty of much of the
information it imparts, or the force and freshness with which obvious
truths are presented.”[2] And as other non-medical reviewers concur
in this decision, I feel bound to attach more weight to them in what
more especially concerns the class of readers to which they belong,
and to retain the whole of the part objected to. In a purely medical
question, on the other hand, I would as unhesitatingly have yielded to
the judgment of the professional critic.
EDINBURGH, 8 ALVA STREET,
_November 1, 1836_.
CONTENTS
PREFACE, xvii
PART I.
PHYSIOLOGY OF DIGESTION.
CHAPTER I.
INTRODUCTORY REMARKS.
Waste or loss of substance always attendant on action--In
the vegetable and animal kingdoms waste is greater than
in the physical--Living bodies are distinguished by
possessing the power of repairing waste--Vegetables, being
rooted in one place, are always in connection with their
food--Animals, being obliged to wander, receive their
food at intervals into a stomach--Nutrition most active
when growth and waste are greatest--In vegetables the
same causes which increase these processes also stimulate
nutrition--But animals require a monitor to warn them
when food is needed--The sense of Appetite answers this
purpose--The possession of a stomach implies a sense of
Appetite to regulate the supplies of food, 1–10
CHAPTER II.
THE APPETITES OF HUNGER AND THIRST.
Hunger and Thirst, what they are--Generally referred to
the stomach and throat, but perceived by the brain--Proofs
and illustrations--Exciting causes of hunger--Common
theories unsatisfactory--Hunger sympathetic of the
state of the body as well as of the stomach--Uses of
appetite--Relation between waste and appetite--Its
practical importance--Consequences of overlooking it
illustrated by analogy of the whole animal kingdom--Disease
from acting in opposition to this relation--Effect
of exercise on appetite explained--Diseased
appetite--Thirst--Seat of Thirst--Circumstances in which it
is most felt--Extraordinary effects of injection of water
into the veins in cholera--Uses of thirst, and rules for
gratifying it, 11–39
CHAPTER III.
MASTICATION, INSALIVATION, AND DEGLUTITION.
Mastication--The teeth--Teeth, being adapted to the
kind of food, vary at different ages and in different
animals--Teeth classed and described--Vitality of teeth
and its advantages--Causes of disease in teeth--Means of
protection--Insalivation and its uses--Gratification of
taste in mastication--Deglutition, 40–57
CHAPTER IV.
ORGANS OF DIGESTION--THE STOMACH--THE GASTRIC
JUICE.
Surprising power of digestion--Variety of sources of
food--All structures, however different, formed from the
same blood--General view of digestion, chymification,
chylification, sanguification, nutrition--The stomach in
polypes, in quadrupeds, and in man--Its position, size,
and complexity, in different animals--Its structure; its
peritoneal, muscular, and villous coats; and uses of
each--Its nerves and bloodvessels; their nature, origins,
and uses--The former the medium of communication between
the brain and stomach--Their relation to undigested
food--Animals not conscious of what goes on in the
stomach--Advantages of this arrangement--The gastric
juice the grand agent in digestion--Its origin and
nature--Singular case of gunshot wound making a permanent
opening into the stomach--Instructive experiments made by
Dr Beaumont--Important results, 58–108
CHAPTER V.
THEORY AND LAWS OF DIGESTION.
Different theories of Digestion--Concoction--Fermentation
--Putrefaction--Trituration--Chemical solution--Conditions
or laws of digestion--Influence of gastric juice.--Experiments
illustrative of its solvent power--Its mode of action on
different kinds of aliment--beef, milk, eggs, soups,
&c.--Influence of temperature--Heat of about 100° essential
to digestion.--Gentle and continued agitation
necessary--Action of stomach in admitting food--Uses
of its muscular motion--Gastric juice acts not only on
the surface of the mass, but on every particle which it
touches--Digestibility of different kinds of food--Table
of results--Animal food most digestible--Farinaceous
next--Vegetables and soups least digestible--Organs
of digestion simple in proportion to concentration
of nutriment--Digestibility depends on adaptation
of food to gastric juice more than on analogy of
composition--Illustrations.--No increase of temperature
during digestion--Dr Beaumont’s summary of inferences, 109–151
CHAPTER VI.
CHYLIFICATION, AND THE ORGANS CONCERNED IN IT.
Chylification--Not well known--Organs concerned in it--The
intestinal canal--Its general structure--Peritoneal
coat--Mesentery--Muscular coat--Uses of these--Air in
intestines--Uses of--Mucous coat--Analogous to skin--The
seat of excretion and absorption--Mucous glands--Absorbent
vessels--Course of chyle towards the heart--Nerves of
mucous coat--Action of bowels explained--Individual
structure of intestines--The Duodenum--Jejunum--and
Ileum--Liver and pancreas concerned in chylification--Their
situation and uses--Bile, its origin and uses--The
pancreas--Its juice--The jejunum described--The
ileum--Cœcum--Colon--and Rectum--Peristaltic motion of
bowels--Aids to it--Digestion of vegetables begins in
stomach but often finished in the bowels--Illustration from
the horse--Confirmation by Dupuytren, 152–183
PART II.
THE PRINCIPLES OF DIETETICS VIEWED IN RELATION
TO THE LAWS OF DIGESTION.
CHAPTER I.
TIMES OF EATING.
The selection of food only one element in sound
digestion--Other conditions essential--Times of eating--No
stated hours for eating--Five or six hours of interval
between meals generally sufficient--But must vary according
to circumstances--Habit has much influence--Proper time
for breakfast depends on constitution, health, and mode of
life--Interval required between breakfast and dinner--Best
time for dinner--Circumstances in which lunch is
proper--Late dinners considered--Their propriety dependent
on mode of life--Tea and coffee as a third meal, useful
in certain circumstances--Supper considered--General rule
as to meals--Nature admits of variety--illustrations--but
requires the observance of principle in our rules, 187–217
CHAPTER II.
ON THE PROPER QUANTITY OF FOOD.
Quantity to be proportioned to the wants of the
system--Appetite indicates these--Cautions in trusting to
appetite--General error in eating too much--Illustrations
from Beaumont, Caldwell, Head, and Abercrombie--Mixtures
of food hurtful chiefly as tempting to excess in
quantity--Examples of disease from excess in servant-girls
from the country, dressmakers, &c.--Mischief from excessive
feeding in infancy--Rules for preventing this--Remarks on
the consequences of excess in grown persons--Causes of
confined bowels explained--And necessity of fulfilling the
laws which God has appointed for the regulation of the
animal economy inculcated, 218–250
CHAPTER III.
OF THE KINDS OF FOOD.
What is the proper food of man?--Food to be adapted
to constitution and circumstances--Diet must vary
with time of life--Diet in infancy--The mother’s
milk the best--Substitutes for it--Over-feeding a
prevalent error--Causes which vitiate the quality
of the milk--Regimen of nurses--Weaning--Diet after
weaning--Too early use of animal food hurtful--Diet of
children in the higher classes too exciting--and produces
scrofula--Mild food best for children--Incessant eating
very injurious--Proper diet from childhood to puberty--It
ought to be full and nourishing but not stimulating--Often
insufficient in boarding-schools--Diet best adapted
for different constitutions in mature age--Regimen
powerful in modifying the constitution, mental as well as
physical--Farther investigation required, 251–287
CHAPTER IV.
CONDITIONS TO BE OBSERVED BEFORE AND AFTER EATING.
General laws of organic activity apply to the stomach as
well as to other parts--Increased flow of blood towards
the stomach during digestion--Hence less circulating in
other organs--and consequently less aptitude for exertion
in them--Bodily rest and mental tranquillity essential
to sound digestion--Rest always attended to before
feeding horses--Hence also a natural aversion to exertion
immediately after eating--Mischief done by hurrying away
to business after meals--Severe thinking hurtful at that
time--Playful cheerfulness after dinner conducive to
digestion--The mind often the cause of indigestion--Its
mode of operation explained--Also influences
nutrition--Illustration from Shakspeare--Importance of
attending to this condition of health enforced, 288–303
CHAPTER V.
ON DRINKS.
Thirst the best guide in taking simple drinks--Thirst
increased by diminution of the circulating fluids--The
desire for liquids generally an indication of their
propriety--Much fluid hurtful at meals--Most useful three
or four hours later--The temperature of drinks is of
consequence--Curious fall of temperature in the stomach
from cold water--Ices hurtful after dinner--Useful in
warm weather, when digestion is completed and caution
used--Cold water more dangerous than ice when the body
is overheated--Tepid drinks safest and most refreshing
after perspiration--Kinds of drink--Water safe for every
constitution--Wine, spirits, and other fermented liquors,
too stimulating for general use, but beneficial in certain
circumstances--Test of their utility, 304–323
CHAPTER VI.
ON THE PROPER REGULATION OF THE BOWELS.
Functions of the intestines--The action of the bowels bears
a natural relation to the kind of diet--Illustrations--And
also to the other excretions--Practical conclusions from
this--Different causes of inactivity of bowels--Natural
aids to intestinal action--General neglect of them--Great
importance of regularity of bowels--Bad health from their
neglect--especially at the age of puberty--Natural means
preferable to purgatives--Concluding remarks, 324–339
INDEX, 341–350
WOOD-CUTS.
Under-jaw, 41.
Thoracic and Abdominal Viscera, 66.
Human Stomach, 67.
Stomach of a ruminating animal, 69.
Villous Coat of the Stomach, 75.
Opening into the stomach of Alexis St Martin, 88.
Abdominal Viscera, 155.
Transverse section of the Abdomen, 157.
Lacteals and Thoracic Duct, 163.
Thoracic Duct, 166.
Contents of the Abdomen after removal of the Intestines, 171.
Mucous Coat of the Duodenum, 172.
PREFACE.
The present volume is essentially a continuation of the work first
published about two years ago, under the title of “The Principles of
Physiology applied to the Preservation of Health and to the Improvement
of Physical and Mental Education;” and its object is the same--namely,
to lay before the public a plain and intelligible description of the
structure and uses of some of the more important organs of the human
body, and to shew how information of this kind may be usefully applied,
not only in the prevention of suffering, but in improving the physical,
moral, and intellectual condition of man.
In “The Principles of Physiology,” the structure and functions of the
skin, muscles, bones, lungs, and nervous system, the laws or conditions
of their healthy action, and the unsuspected origin of many of their
diseases in infringements of these laws, were explained in succession
at considerable length; and the means by which their health and
efficiency might best be secured were pointed out. It was stated that,
in selecting these organs as subjects for discussion, I had been guided
by the desire to notice in preference those functions which are most
influential in their operation on the general system, and at the same
time least familiarly known; and that, if the attempt to convey the
requisite information in a manner suited to the general reader should
prove successful, I would afterwards prepare a similar account of
others, in the right understanding and management of which our interest
is not less deeply involved, but in regard to which much ignorance
continues nevertheless to prevail, even among the most liberally
educated classes of society.
The numerous proofs which I received of the utility of my former
work, not only from professional and literary journals, but also from
individuals previously unknown to me,--many of them guardians and
instructors of youth, speaking from personal experience,--together with
the rapid sale of four large editions in little more than two years,
soon completely satisfied me that I had neither been deceived as to
the real importance of physiological knowledge to the general public,
nor been altogether unsuccessful in the method of conveying it. Thus
encouraged, accordingly, I cheerfully resumed my labours, and, from
materials which had been long accumulating, began the preparation of
the treatise now submitted to the indulgent consideration of the reader.
The matters discussed on the present occasion relate chiefly to
the function of Digestion and the principles of Dietetics; and in
selecting them I have been guided by the same principle as before. It
may, at first sight, be doubted whether I have not exceeded proper
bounds in thus dedicating a whole volume to the consideration of a
single subject; but the more we consider the real complication of the
function of Digestion,--the extensive influence which it exercises at
every period of life over the whole of the bodily organization,--the
degree to which its morbid derangements undermine health, happiness,
and social usefulness,--and especially the share which they have in
the production of scrofulous and consumptive as well as of nervous
and mental affections,--we shall become more and more convinced of
the deep practical interest which attaches to a minute acquaintance
with the laws by which it is regulated. In infancy, errors in diet,
and derangement of the digestive organs, are admitted to be among the
principal causes of the striking mortality which occurs in that period
of life. In youth and maturity, the same influence is recognised,
not only in the numerous forms of disease directly traceable to that
origin, but also in the universal practice of referring every obscure
or anomalous disorder to derangement of the stomach or bowels. Hence,
too, the interest which has always been felt by the public in the
perusal of books on Dietetics and Indigestion; and hence the prevailing
custom of using purgatives as remedies for every disorder, very often
with good, but not unfrequently with most injurious effects.
Numerous and popular, however, as writings on Dietetics have been, and
excellent as are many of the precepts which have been handed down by
them from the earliest ages, sanctioned by the warm approval of every
successive generation, it is singular how very trifling their influence
has been, and continues to be, in altering the habits of those to whom
they are addressed. In a general way, we all acknowledge that diet
is a powerful agent in modifying the animal economy; yet, from our
_conduct_, it might justly be inferred, that we either regarded it
as totally devoid of influence, or remained in utter ignorance of its
mode of operation, being left to the guidance of chance alone, or of
notions picked up at random, often at variance with reason, and, it may
be, in contradiction even with our own daily experience.
It has been alleged by a friendly critic of the first edition, that
the author is too sanguine in expecting that the mere communication
of knowledge will suffice to alter the habits of the race, and that,
although the information conveyed in the present volume may be turned
to account by third parties--by mothers and nurses, for example--“yet
with respect to the direct effect upon eaters,” slender results
must be anticipated. “The world,” it is wittily added, “will read,
admire, and applaud Dr Combe on Digestion and Dietetics, and then go
on in its usual way _eating what it likes, and digesting what it
can_.” The Author, however, never entertained the hope that his
work would immediately produce the slightest perceptible change in the
general practices of society, or that many healthy men of mature age
and confirmed habits would forsake their accustomed regimen merely
because it was shewn to be at variance with the laws of Nature. But
as human conduct is in some measure influenced by knowledge, he is
still confident enough to believe, that, among valetudinarians and
the young of both sexes, whose habits are not formed, and numbers of
whom err as much from ignorance as from the force of passion, many
may be found who will be glad to obtain the guidance of knowledge and
principle in the regulation of their mode of life; and that even many
parents, who may not have resolution enough to forsake mischievous
indulgences to which they have long been accustomed, may nevertheless
be anxious to avail themselves of any assistance on which they can
depend for the better bringing up of their children. If in these
expectations he is not too sanguine, the future advantage to the race
from the present diffusion of dietetic knowledge is as certain, and
almost as encouraging, as if its effects were instantaneous on both old
and young. In the march of human improvement, months and years count
but as moments. The _men_ of to-day will soon have acted their
part, and give place to those who are now with youthful energy adding
to their knowledge, and throwing off a portion of the prejudices of
their fathers. They in their turn will speedily be succeeded by their
children, and the discoveries of the one generation will thus become
the established and influential truths of the next. Each individual
change in the habits of society may be so slow and minute as at the
moment to escape our notice, but it is not on that account the less
real. Nobody who compares the coarse feeding and riotous convivialities
of our forefathers, at the beginning of last century, with the more
refined and temperate habits of the present day, will think of denying
that a prodigious step has been made in the interval even with respect
to eating and drinking, which the critic seems to consider as so much
beyond the influence of reason. And yet, if we take any single year
of the whole century, we shall be unable to particularize any marked
reformation which took place within its limits. This being the case,
then, can we, their descendants, maintain that we are arrived so nearly
at perfection as to leave no room for corresponding improvement in
our day? My conviction is so much the reverse, that it seems to me
certain that our onward progress will continue through generations yet
unborn, with the same steadiness as it has done through generations
long since gathered to their fathers; and that every attempt made to
render man better acquainted with the laws of his own constitution, and
thereby provide him with fixed and better principles of action, will
exert a positive and decided influence on the progress of the race,
proportioned in extent to the _truth_, clearness, and general
applicability of the views which are unfolded. On such considerations
do I ground my hope that the present volume, notwithstanding its
numerous defects, will (in so far as it really embodies truths of
practical importance) contribute in its own limited sphere to the
general end.
The real cause of the little regard paid to dietetic rules--and it
is of consequence to remark it--is not so much indifference to their
influence, or even the absolute want of valuable information, as the
faulty manner in which the subject is usually considered. In many of
our best works, _the relation subsisting between the human body
on the one hand, and the qualities of alimentary substances on the
other_, is altogether lost sight of, although it is the only
solid principle on which their proper adaptation to each other can be
based. In this manner, while the attention is carefully directed to
the consideration of the abstract qualities of the different kinds of
aliment, little or no regard is paid to the relation in which they
stand to the individual constitution, as modified by age, sex, season,
and circumstances, or to the observance of the fundamental laws of
digestion. And hence, although these conditions are not unfrequently
of much greater importance to the general health than even the right
selection of food, yet, when indigestion arises from neglecting them,
the food alone is blamed, and erroneous conclusions are drawn, by
relying on which, upon future occasions, we may easily be led into
still more serious mistakes.
It is, indeed, from being left in this way without any guiding
principle to direct their experience, and test the accuracy of the
precepts laid down to them for the regulation of their conduct, that
many persons begin by being bewildered by the numerous discrepancies
which they meet with between facts and doctrine, between counsel and
experience,--and end by becoming entirely sceptical on the subject of
all dietetic rules whatever, and regarding them as mere theoretical
effusions, based on fancy, and undeserving of a moment’s consideration.
The true remedy for this state of things is, not to turn away
in disgust and despair, but to resort to a more rational mode of
inquiry--certain that, in proportion as we advance, some useful
result will reward our labours. Such, accordingly, has been my aim
in the present publication; and if I shall be found to have been
even moderately successful in attaining it, I shall rejoice in the
confident conviction that others will be led to still more positive and
beneficial results. Utility has been my great object throughout. In
following what I conceive to be an improved mode of investigation, I
have in some instances placed known facts in a new point of view, and
deduced from them practical inferences of considerable value and easy
application: but beyond this, I lay no claim to originality; and if I
have any where used expressions which may seem either to do injustice
to others or to arrogate too much credit to myself, it has been
entirely without any such design, and, consequently, I will be prompt
to acknowledge my error and rectify the involuntary mistake.
In preparing the present volume for the press, I have derived the
utmost advantage from a very valuable work by Dr Beaumont, an American
writer, which--though faulty in its arrangement, and necessarily
defective in many essential particulars--contains an authentic record
of some of the most curious and instructive observations which have
ever been made on the process of digestion. That excellent and
enlightened physiologist had the rare good fortune to meet with a
case where an artificial opening into the stomach existed, through
which he could see every thing that took place during the progress of
healthy digestion; and, with the most disinterested zeal and admirable
perseverance, he proceeded to avail himself of the opportunity thus
afforded of advancing human knowledge, by engaging the patient, at
a heavy expense, to live with him for several years, and become the
subject of numerous and carefully conducted experiments. Of the results
thus obtained, I have not scrupled to make the freest and most ample
use--not from considering them as positively new (for even Dr Beaumont
lays little claim to the merit of a discoverer), but because they come
before us so entirely freed from the numerous sources of error and
doubt which formerly impaired their value, that they can now, for the
first time, be safely trusted as practical guides in the science of
dietetics. From Dr Beaumont’s work, also, being still inaccessible to
the British reader, it is a bare act of justice towards him, and also
the best way of fulfilling the objects he had in view, to make its
contents known as widely as possible: for wherever they are known, they
will be acknowledged to redound to his credit, not less as a man than
as a philosopher.
Objections have been stated to several of the repetitions which occur
in the following pages. The only apology I have to offer for them is,
that I committed them deliberately, because they seemed to me necessary
to ensure clearness, and because the intimate manner in which the
different functions are connected with each other, sometimes made it
impossible to explain one without again referring to the rest. My prime
objects being to render the meaning unequivocally plain, and impress
the subject deeply upon the reader’s mind, I thought it better to risk
in this way the occasional repetition of an important truth, than to
leave it in danger of being vaguely apprehended, or its true value
unperceived. For these reasons, it is hoped that the fault--if such it
is--will be leniently overlooked.
Those who wish to study more fully the subject of Dietetics, will find
much useful information in Dr Hodgkin’s “Lectures on the Means of
Promoting and Preserving Health;” Professor Dunglison “On the Influence
of Atmosphere and Locality, Change of Air and Climate, Seasons,
Food, Clothing, Bathing, Exercise, Sleep, Corporeal and Intellectual
Pursuits, &c. &c. &c. on Human Health;” Dr Paris “On Diet;” and Dr
Kilgour’s “Lectures on the Ordinary Agents of Life, as applicable to
Therapeutics and Hygiène.”
CHAPTER I.
GENERAL VIEW OF THE OBJECTS AND LAWS OF NUTRITION.
Waste or loss of substance always attendant on action.--In
the vegetable and animal kingdoms waste is greater than in
the physical.--Living bodies are distinguished by possessing
the power of repairing waste.--Vegetables, being rooted in
one place, are always in connexion with their food.--Animals,
being obliged to wander, receive their food at intervals into
a stomach.--Nutrition most active when growth and waste are
greatest.--In vegetables the same causes which increase these
processes also stimulate nutrition.--But animals require a
monitor to warn then when food is needed.--The sense of Appetite
answers this purpose.--The possession of a stomach implies a
sense of Appetite to regulate the supplies of food.
Throughout every department of Nature waste is the invariable result of
action. Even the minutest change in the relative position of inanimate
objects cannot be effected without some loss of substance. So well is
this understood, that it is an important aim in mechanics to discover
the best means of reducing to the lowest possible degree the waste
consequent upon motion. Entirely to prevent it is admitted to be beyond
the power of man; for, however nicely parts may be adjusted to each
other, however hard and durable their materials, and however smoothly
motion may go on, still in the course of time loss of substance
becomes evident, and repair and renewal become indispensable to the
continuance of the action.
It is thus a recognised fact, or general law of nature, that nothing
can act or move without undergoing some change, however trifling in
amount. Not even a breath of wind can pass along the surface of the
earth without altering in some degree the proportions of the bodies
with which it comes into contact; and not a drop of rain can fall
upon a stone without carrying away some portion of its substance. The
smoothest and most accurately formed wheel, running along the most
level and polished railroad, parts with some portion of its substance
at every revolution, and in process of time is worn out and requires to
be replaced. The same effect is forcibly, though rather ludicrously,
exemplified in the great toe of the bronze statue of St Peter at Rome,
which in the course of centuries has been worn down to less than half
its original size by the successive kisses of the faithful; and I
venture to mention it, because it affords one of the best specimens
of the operation of a principle, the existence of which, from the
imperceptibly small effect of any single act, might otherwise be
plausibly denied.
As regards _dead_ or _inanimate_ matter, the destructive
influence of action is constantly forced upon our attention by every
thing passing around us; and so much human ingenuity is exercised to
counteract its effects, that no reflecting person will dispute the
universality of its operation. But when we observe shrubs and trees
waving in the wind, and animals undergoing violent exertion, for year
after year, and yet both continuing to increase in size, we may be
inclined, on a superficial view, to regard _living_ bodies as
constituting exceptions to the rule. On more careful examination,
however, it will appear that waste goes on in living bodies not only
without any intermission, but with a rapidity immeasurably beyond
that which occurs in inanimate objects. In the vegetable world, for
instance, every leaf of a tree is incessantly pouring out some portion
of its fluids, and every flower forming its own fruit and seed,
speedily to be separated from and lost to its parent stem; thus causing
in a few months an extent of waste many hundred times greater than
what occurs in the same lapse of time after the tree is cut down, and
all its living operations are at a close. The same thing holds true in
the animal kingdom. So long as life continues, a copious exhalation
from the skin, the lungs, the bowels, and the kidneys, goes on without
a moment’s intermission; and not a movement can be performed which
does not at least partially increase the velocity of the circulation,
and add something to the general waste. In this way, during violent
exertion several ounces of the fluids of the body are sometimes thrown
out by perspiration in a very few minutes; whereas, after life is
extinguished, all the excretions cease, and waste is limited to that
which results from ordinary chemical decomposition.
So far, then, the law that waste is attendant on action, applies
to both dead and living bodies; but beyond this point a remarkable
difference between them presents itself. In the physical or inanimate
world, what is once lost or worn away is lost for ever. There is no
power inherent in the piston of the steam-engine by which it can
repair its own loss of particles; and consequently in the course of
time it must either be laid aside as useless, or be remodelled by the
hand of the workman. But _living_ bodies, whether vegetable or
animal, possess the distinguishing characteristic of being able to
repair their own waste and add to their own substance. The possession
of such a power is in fact essential to their very existence. If
the sunflower, which in fine weather exhales thirty ounces of fluid
between sunrise and sunset, contained no provision within its own
structure for replacing this enormous waste, it would necessarily
shrivel and die within a few hours, as it actually does when plucked
up by the roots; and, in like manner, if man, whose system throws out
every day five or six pounds of substance by the ordinary channels of
excretion, possessed no means of repairing the loss, his organization
would speedily decay and perish. This very result is frequently
witnessed in cases of shipwreck and other disasters, where, owing
to the impossibility of obtaining food, death ensues from the body
wasting away till it becomes incapable of carrying on the operations
of life. In some instances this waste has even proceeded so far that
three-fourths of the whole weight of the body have been lost before
life became extinct.
It is impossible to reflect on these facts, and others of a similar
kind, without having the conviction forced upon our minds, that in
every department of nature expenditure of material is inseparable from
action, and that, in living bodies, waste goes on so rapidly, and by
so many different channels, that life could not be maintained for any
length of time without an express provision being made for compensating
its occurrence.
In surveying the respective modes of existence of vegetables and of
animals, with the view of ascertaining by what means this compensation
is effected, the first striking difference between them which we
perceive, is the fixity of position of the one, and the free locomotive
power of the other. The vegetable grows, flourishes, and dies, fixed to
the same spot of earth from which it sprang; and, however much external
circumstances may change around it, it must remain and submit to their
influence. If it be deprived of moisture and solar heat and light, it
cannot go in search of them, but must remain to droop and to perish. If
the earth to which its roots are attached be removed, and a richer soil
be substituted than that which its nature requires, it still has no
option: it must grow up in rank and unhealthy luxuriance, in obedience
to an impulse which it cannot resist. At all hours and at all seasons
it is at home, and in direct communication with the soil from which its
nourishment is extracted. And being thus without ceasing in contact
with its food, it requires no storehouse in which to lay up provision,
but receives immediately from the earth, and at every moment, all that
is necessary for its sustenance.
But it is otherwise with animals. These not only enjoy the privilege of
locomotion, but are compelled to use it, and often to go to a distance,
in search of food and shelter. Consequently, if their vessels of
nutrition were like those of vegetables in direct communication with
external substances, they would be torn asunder at every movement,
and the animals themselves exposed either to die from starvation,
or to forego the exercise of the higher functions for which their
nature is adapted. But the necessity for a constant change of place
being imposed on them, a different arrangement became indispensable
for their nutrition: and the method by which the Creator has remedied
the inconvenience is not less admirable than simple. To enable the
animal to move about and at the same time to maintain a connexion
with its food, He has provided it with a receptacle or stomach, where
it is able to store up a supply of materials from which sustenance
may be gradually elaborated during a period of time proportioned
to its necessities and mode of life. It thus _carries along with
it_ nourishment adequate to its wants; and the small nutritive
vessels imbibe their food from the internal surface of the stomach
and bowels, where the nutriment is stored up, just as the roots or
nutritive vessels of vegetables do from the soil in which they grow.
The possession of a stomach or receptacle for food is accordingly
a characteristic of the animal system as contrasted with that of
vegetables; it is found even in the lowest orders of zoophytes, which
in other respects are so nearly allied to plants.
The sole objects of nutrition being to repair waste and to admit
of growth, Nature has so arranged that within certain limits it is
always most vigorous when growth or waste proceeds with the greatest
rapidity. Even in vegetables this relation is distinctly observable.
In spring and summer, when vegetative life is most active, and when
leaves, flowers, and fruit, are to be formed, and growth carried on,
nourishment is largely drawn from the soil, and the elaboration and
circulation of the sap are proportionally vigorous; whereas in winter,
when the leaves and flowers have passed away, and vegetable life is
in repose, little nourishment is needed, and the circulation of the
sap is proportionally slow. In accordance with these facts, every one
will recollect how freely a shrub or a tree bleeds, as it is called,
when its bark is cut early in the season, and how dry it becomes on the
approach of winter. It is the activity of the circulation in summer
which renders its temporary suspension by transplanting so generally
fatal at that season; whereas, owing to the comparative sluggishness
with which it is carried on in winter, its partial interruption is then
attended with much less risk.
In vegetables, the quantity of nourishment taken in entirely depends
on, and is regulated by, the circumstances in which they are placed.
When they are exposed, as in spring and summer, to the stimulus of
heat and light, all their functions are excited, waste and growth
are accelerated, and a more abundant supply of nourishment becomes
indispensable to their health and existence; and hence, in a dry
soil incapable of affording a copious supply of sap, they speedily
wither and die. Exposed to cold, on the other hand, and shaded from
the light, their vitality is impaired, and the demand for nourishment
greatly diminished. This is uniformly the case in winter; and many
circumstances shew that the change is really owing to the causes
mentioned above, and not to any thing inherent in the constitution of
the vegetable itself. In tropical climates, for example, where heat,
light, and moisture abound, vegetable life is ever active, and the
foliage ever thick and abundant; and even in our own northern region,
we are able by artificial heat so far to anticipate the natural order
of the seasons, as to obtain the ripened fruit of the vine in the very
beginning of spring. The whole system of _forcing_ vegetables and
fruit, so generally resorted to for the early supply of our markets,
is, in truth, founded on the principle we are now discussing; and by
the regulated application of heat, light, and moisture, we are able to
hasten or to retard, to a very considerable extent, the ordinary stages
of vegetable life. But to ensure success in our operations, we must be
careful to proportion the supply of nourishment to the state of the
plant at the time. If, by the application of heat, we have stimulated
it to premature growth and foliage, we must at the same time provide
for it an adequate supply of food, otherwise its activity will exhaust
itself, and induce premature decay. Hence the regular watering which
greenhouse plants require. But if we have retarded its progress and
lowered its vitality by excluding heat and light, the same copious
nourishment will not only be unnecessary, but will probably do harm by
inducing repletion and disease.
In vegetables, the absorption of food is thus regulated chiefly by
the circumstances of heat, moisture, and light, under which the
plant is placed, and by the consequent necessity which exists at the
time for a larger or smaller supply of nourishment to carry on the
various processes of vegetable life. According to this arrangement,
nutrition is always most active when the greatest expenditure of
material is taking place. When growth is going on rapidly, and the
leaves are unfolding themselves, sap is sucked up from the earth in
immense quantity; but when these processes are completed as summer
advances, and almost no fresh materials are required, except for
the consolidation of the new growth and the supply of the loss by
exhalation, a much smaller amount of nourishment suffices, and the sap
no longer circulates in the same profusion. In autumn, again--when
the fruit arrives at maturity, the leaves begin to drop off, and the
activity of vegetable life suffers abatement--nutrition is reduced
to its lowest ebb; and in this state it continues till the return of
spring stimulates every organ to new action, and once more excites a
demand for an increased supply.
Nor is the same great principle, of supply requiring to be proportioned
to demand, less strikingly apparent in animals. Wherever growth is
proceeding rapidly, or the animal is undergoing much exertion and
expenditure of material, an increased quantity of food is invariably
required; and, on the other hand, where no new substance is forming,
and where, from bodily inactivity, little loss is sustained, a
comparatively small supply will suffice. But as animals are subjected
to much more rapid and violent transitions from activity to inactivity
than vegetables are--and thus require to pass more immediately from
one kind and quantity of nourishment to another, in order to adapt
their nutrition to the ever-varying demands made upon the system--they
evidently stand in need of some provision to enforce attention when
nourishment is necessary, and to enable them always to proportion the
supply to the real wants of the body. Not being, like vegetables, in
constant connection with their aliment, they might suffer from neglect
if they did not possess some contrivance to warn them in time when to
seek and in what quantity to consume it. But in endowing animals with
the sense of _Appetite_, or the sensations of _Hunger_ and
_Thirst_ generally included under it, the Creator has guarded
effectually against the inconvenience, and given to them a guide in
every way sufficient for the purpose.
The very possession of a stomach or receptacle, into which food
sufficient for a shorter or longer period can be introduced at one
time, and which we have already remarked as characterizing all animals
from the lowest to the highest, almost necessarily implies the
co-existence of some watchful monitor, such as appetite, to enforce
attention to the wants of the system, with an earnestness which it
shall not be easy to resist. If this were not the case in man, for
example--if he had no motive more imperative than reason to oblige
him to take food--he would be constantly liable, from indolence and
thoughtlessness, or the pressure of other occupations, to incur the
penalty of starvation, without being previously aware of his danger.
But the Creator, with that beneficence which distinguishes all His
works, has not only provided an effectual safeguard in the sensations
of hunger and thirst, but moreover, attached to their regulated
indulgence a degree of pleasure which never fails to insure attention
to their demands, and which, in highly civilized communities, is apt
to lead to excessive gratification. Such being the important charge
committed to the appetites of hunger and thirst, it will be proper to
submit to the reader, before entering upon the consideration of the
more complicated process of digestion, a few remarks on their nature
and uses.
CHAPTER II.
THE APPETITES OF HUNGER AND THIRST.
Hunger and Thirst, what they are--Generally referred to the
stomach and throat, but perceived by the brain--Proofs and
illustrations--Exciting causes of hunger--Common theories
unsatisfactory--Hunger sympathetic of the state of the body
as well as of the stomach--Uses of appetite--Relation between
waste and appetite--Its practical importance--Consequences
of overlooking it illustrated by analogy of the whole
animal kingdom--Disease from acting in opposition to this
relation--Effect of exercise on appetite explained--Diseased
appetite--Thirst--Seat of Thirst--Circumstances in which it is
most felt--Extraordinary effects of injection of water into the
veins in cholera--Uses of thirst, and rules for gratifying it.
In the preceding chapter, I endeavoured to shew, _first_, that
nutrition is required only because waste, and a deposition of new
particles, are continually going on, so that the body would speedily
become exhausted if its constituent materials were not renewed;
_secondly_, that the sense of appetite is given to animals for
the express purpose of warning them when a fresh supply of aliment is
needed--as, without some such monitor, they would be apt to neglect
the demands of nature; and _thirdly_, that vegetables have no
corresponding sensation, simply because, from their being at all times
in communication with the soil, their nutrition goes on continuously in
proportion as it is necessary, and without requiring any prompter to
put it in action at particular times.
If these principles be correct, it follows that, in the healthy state
(and let the reader be once for all made aware that in the following
pages the state of health is always implied, except where it is
otherwise plainly expressed), the dictates of appetite will not be
every day the same, but will vary according to the mode of life and
wants of the system, and, when fairly consulted, will be sufficient to
direct us both at what time and in what quantity we ought to take in
either solid or liquid sustenance. But to make this perfectly evident,
a few general observations may be required.
It is needless to waste words in attempting to describe what hunger
and thirst are: every one has felt them, and no one could understand
them without such experience, any more than sweetness or sourness
could be understood without tasting sweet or sour objects. Their end
is manifestly to proclaim that farther nourishment is required for the
support of the system; and our first business is, therefore, to explain
their nature and seat, in so far at least as a knowledge of these may
be conducive to our welfare.
The sensation of hunger is commonly referred to the stomach, and that
of thirst to the upper part of the throat and back of the mouth;
and correctly enough to this extent, that a certain condition of
the stomach and throat tends to produce them. But, in reality, the
sensations themselves, like all other mental affections and emotions,
have their seat in the brain, to which a sense of the condition of
the stomach is conveyed through the medium of the nerves. In this
respect, Appetite resembles the senses of Seeing, Hearing, and Feeling;
and no greater difficulty attends the explanation of the one than of
the others. Thus, the cause which excites the sensation of colour, is
certain rays of light striking upon the nerve of the eye; and the cause
which excites the perception of sound, is the atmospherical vibrations
striking upon the nerve of the ear; but the sensations themselves take
place in the brain, to which, as the organ of the mind, the respective
impressions are conveyed. In like manner, the cause which excites
appetite is an impression made on the nerves of the stomach; but the
feeling itself is experienced in the brain, to which that impression is
conveyed. Accordingly, just as in health no sound is ever heard except
when the external vibrating atmosphere has actually impressed the
ear, and no colour is perceived unless an object be presented to the
eye,--so is appetite never felt, except where, from want of food, the
stomach is in that state which forms the proper stimulus to its nerves,
and where the communication between it and the brain is left free and
unobstructed.
But as, in certain morbid states of the brain and nerves, voices and
sounds are heard, or colours and objects are seen, when no external
cause is present to act upon the ear or the eye,--so, in disease, a
craving is often felt when no real want of food exists, and where,
consequently, indulgence in eating can be productive of nothing but
mischief. Such an aberration is common in nervous and mental diseases,
and not unfrequently adds greatly to their severity and obstinacy.
In indolent unemployed persons, who spend their days in meditating
on their own feelings, this craving is very common, and from being
regarded and indulged as if it were healthy appetite, is productive of
many dyspeptic affections.[3]
If the correctness of the preceding explanation of the sensation of
hunger be thought to stand in need of confirmation, I would refer to
the very conclusive experiments by Brachet of Lyons, as setting the
question entirely at rest. Brachet starved a dog for twenty-four hours,
till it became ravenously hungry, after which he divided the nerves
which convey to the brain a sense of the condition of the stomach.
He then placed food within its reach, but the animal, which a moment
before was impatient to be fed, went and lay quietly down, as if hunger
had never been experienced. When meat was brought close to it, it began
to eat; and, apparently from having no longer any consciousness of the
state of its stomach--whether it was full or empty--it continued to
eat till both it and the gullet were inordinately distended. In this,
however, the dog was evidently impelled solely by the _gratification
of the sense of taste_; for on removing the food at the beginning
of the experiment to the distance of even a few inches, it looked on
with indifference, and made no attempt either to follow the dish or to
prevent its removal.[4]
Precisely similar results ensued when the nervous sympathy between the
stomach and brain was arrested by the administration of narcotics. A
dog suffering from hunger turned listlessly from its food when a few
grains of opium were introduced into its stomach. It may be said that
such a result is owing to the drug being absorbed and carried to the
brain through the ordinary medium of the circulation; but Brachet has
proved that this is not the case, and that the influence is primarily
exerted upon the nerves. To establish this point, two dogs of the
same size were selected. In one the nerves of communication were
left untouched, and in the other they were divided. Six grains of
opium were then given to each at the same moment. The sound dog began
_immediately_ to feel the effects of the opium and became stupid,
while the other continued lying at the fireside for a long time,
without any unusual appearance except a little difficulty of breathing.
In like manner, when the experiment was repeated with that powerful
poison _nux vomica_, upon two dogs similarly circumstanced, the
sound one fell _instantly_ into convulsions, while the other
continued for a long time as if nothing had happened.
These results demonstrate, beyond the possibility of doubt, the
necessity of a free nervous communication between the stomach and
brain, for enabling us to experience the sensation of hunger. The
connexion between the two organs is indeed more widely recognised in
practice than it is in theory; for it is a very common custom with the
Turks to use opium for abating the pangs of hunger when food is not to
be had, and sailors habitually use tobacco for the same purpose. Both
substances act exclusively on the nervous system.
The relation thus shewn to subsist between the stomach and the brain,
enables us in some measure to understand the influence which strong
mental emotions and earnest intellectual occupation exert over
the appetite. A man in perfect health, sitting down to table with
an excellent appetite, receives a letter announcing an unexpected
calamity, and instantly turns away with loathing from the food which,
a moment before, he was prepared to eat with relish; while another,
who, under the fear of some misfortune, comes to table indifferent
about food, will eat with great zest on his “mind being relieved,” as
the phrase goes, by the receipt of pleasing intelligence. Excessive
and absorbing emotion, even of a joyful kind, has the same effect.
Captain Back tells us in the interesting narrative of his last journey,
that when he first heard of Captain Ross’s return, “the thought of
so wonderful a preservation overpowered, for a time, the common
occurrences of life. _We had but just sat down to breakfast, but
our appetite was gone_, and the day passed in a feverish state of
excitement,” (P. 245). In such cases, no one will imagine that the
external cause destroys appetite otherwise than through the medium
of the brain. Occasionally, indeed, the aversion to food amounts to
a feeling of loathing and disgust, and even induces sickness and
vomiting,--a result which depends so entirely on the state of the
brain, that it is often excited by mechanical injuries of that organ.
The analogy between the external senses and the appetite is in various
respects very close. If we are wrapt in study, or intent on any scheme,
we become insensible to impressions made on the ear or eye. A clock may
strike, or a person enter the room, without our being aware of either
event. The same is the case with the desire for food. If the mind is
deeply engaged, the wants of the system are unperceived and unattended
to--as was well exemplified in the instance of Sir Isaac Newton, who,
from seeing the bones of a chicken lying before him, fancied that
he had already dined, whereas, in reality, he had eaten nothing for
many hours. Herodotus ascribes so much efficacy to mental occupation
in deadening the sense of hunger, that he speaks of the inhabitants
of Lydia having successfully had recourse to gaming as a partial
substitute for food, during a famine of many years continuance. In this
account there is, of course, gross exaggeration; but it illustrates
sufficiently well the principle under discussion.
Many attempts have been made but without much success, to determine
what the peculiar condition of the stomach is which excites in the
mind the sensation of hunger. For a long time it was imagined that
the presence of _gastric_ or _stomach_ juice, irritating
the nerves of the mucous membrane, was the exciting cause; but it
was at last ascertained, that, after the digestion of a meal is
completed, and the chyme has passed into the intestine, the gastric
juice ceases to be secreted till _after_ a fresh supply of food
has been taken in.[5] It was next supposed that the mere emptiness of
the stomach was sufficient to excite hunger, and that the sensation
arose partly from the opposite sides rubbing against each other.
But this theory is equally untenable; for the stomach generally
contains a sufficient quantity of air to prevent the actual contact
of its sides, and moreover it may be entirely void of food and yet
no appetite be felt. It may be laid down, indeed, as a general rule,
that an interval of rest must follow the termination of digestion
before the stomach becomes fit to resume its functions, or appetite is
experienced in any degree of intensity; and the length of time required
for this purpose varies very much, according to the mode of life and
to the extent of waste going on in the system. In many diseases,
too, the stomach remains empty for days in succession, without any
corresponding excitation of hunger. Even in healthy sedentary people,
whose expenditure of bodily substance is small, real appetite is not
felt till long after the stomach is empty, and hence one of their most
common complaints is the want of appetite.
Dr Beaumont suggests a distended state of the vessels which secrete the
gastric juice as the exciting cause of hunger, and thinks that this
view is strengthened by the rapidity with which the juice is poured
out after a short fast--a rapidity, he says, which cannot be accounted
for except by supposing the juice to have existed ready made in the
vessels or follicles by which it is secreted. But this theory is not
more satisfactory than the rest, for in the sudden flow of saliva into
the mouth of a hungry man on the unexpected appearance of savoury
viands, we have an instance of equally rapid secretion where there
was evidently no storing up beforehand, Besides, there is an obvious
relation between appetite and the wants of the system, which is not
always taken sufficiently into account, and which is nevertheless too
important to be overlooked.
If the body be very actively exercised, and a good deal of waste be
effected by perspiration and exhalation from the lungs, the appetite
becomes keener, and more urgent for immediate gratification; and if
it is indulged, we eat with a relish unknown on other occasions, and
afterwards experience a sensation of _bien-être_ or internal
comfort pervading the frame, as if every individual part of the body
were imbued with a feeling of contentment and satisfaction, the very
opposite of the restless discomfort and depression which come upon
us, and extend over the whole system, when appetite is disappointed.
An amusing example of the principle here inculcated is to be found
in the _Correspondance Inedite de Madame du Deffand_,[6] where
she describes her friend Madame de Pequigni as an insatiable bustling
little woman who consumes two hours every day in devouring her dinner,
and “_eats like a wolf_.” But, then, remarks Madame du Deffand
by way of explanation, “_Il est vrai qu’elle fait un exercice
enragé_.”
There is, in short, an obvious and active sympathy between the
condition and bearing of the stomach and those of every part of
the animal frame--in virtue of which, hunger is felt very keenly
when the general system stands in urgent need of repair, and very
moderately when no waste has been suffered. This principle is
strikingly illustrated during recovery from a severe illness. “In
convalescence from an acute disease,” as is well remarked by Brachet,
“the stomach digests vigorously, and yet the individual is always
hungry. This happens because all the wasted organs and tissues demand
the means of repair, and demand them from the stomach, which has
the charge of sending them; and, therefore, they keep up in it the
continual sensation of want, which, however, is, in this case, only
sympathetic of the state of the body.”[7] In alluding to this subject,
Blaine observes, that “Hunger and thirst can only be satisfactorily
explained by considering them as properties in the stomach by which it
sympathizes with the wants of the constitution; and hence it is, that
food taken in invigorates, even before it can be digested.”[8] Hence
also the prostration of strength that is felt when the stomach has been
for some time empty.
This sympathy is sometimes singularly manifest even in disease. In
some cases of affection of the mesenteric glands, for example, where
stomachic digestion remains for a time pretty healthy, and the general
system suffers chiefly from the want of nourishment caused by the
passage of the chyle into the blood being obstructed, the appetite
continues as keen and often keener than before; because the system,
being in want of nourishment, and the stomach healthy, all its natural
causes continue to act as before; and accordingly, when food is taken,
it is digested there as usual, but the chyle which is formed from it
in the intestine can no longer be transmitted through the swollen
glands in its usual healthy manner, to be converted into nutritive
blood in the lungs; and the system thus failing to receive the required
supply, recommences its cravings almost as soon as if no food had been
obtained. When the disease has advanced a certain length, however,
fever springs up, and destroys both appetite and digestion.
The effects of exercise, also, shew very clearly the connexion between
appetite and the state of the system. If we merely saunter out for a
given time every day, without being actively enough engaged to quicken
the circulation and induce increased exhalation from the skin and
lungs, we come in with scarcely any change of feeling or condition;
whereas, if we exert ourselves sufficiently to give a general impetus
to the circulation, and bring out moderate perspiration, but without
inducing fatigue, we feel a lightness and energy of a very pleasurable
description, and generally accompanied by a strong desire for food.
Hence the keen relish with which the fox-hunter sits down to table
after a successful chase.
This intimate communion between the state of the system and that of the
stomach is a beautiful provision of Nature, and is one of the causes of
the ready sympathy which has often been remarked as existing between
the stomach and all the other organs--in other words, of the readiness
with which they accompany it in its departure from health, and the
corresponding aptitude of _their_ disorders to produce derangement
of the digestive function. Apparently for the purpose, among others,
of thus intimately connecting the stomach with the rest of the system,
it is supplied with a profusion of nervous filaments of every kind,
which form a closely-interwoven nervous network in its immediate
neighbourhood, and the abundance of which accounts for the severe and
often suddenly fatal result of a heavy blow on the pit of the stomach.
Without pretending to determine what the precise condition of the
nerves of the stomach is, which, when conveyed to the brain, excites
the sensation of appetite, I think it sufficient for every practical
purpose if we keep in mind, that _the co-operation of the nervous
system is necessary for the production of appetite_, and that
_there is a direct sympathy between the stomach and the rest of the
body_, by means of which the stimulus of hunger becomes unusually
urgent where the bodily waste has been great, although a comparatively
short time has elapsed since the preceding meal.
Appetite, then, being given for the express purpose of warning as
when a supply of food is necessary, it follows that its call will
be experienced in the highest intensity when waste and growth--or,
in other words, the operations which demand supplies of fresh
materials--are most active; and in the lowest intensity when, from
indolence and the cessation of growth, the demand is least. In youth,
accordingly, when bodily activity is very great, and a liberal supply
of nourishment is required both to repair waste and to carry on growth,
the appetite is keener and less discriminating than at any other period
of life, and, what is worthy of remark, as another admirable instance
of adaptation, _digestion is proportionally vigorous and rapid_,
and abstinence is borne with great difficulty; whereas, in mature age,
when growth is finished and the mode of life more sedentary, the same
abundance of aliment is no longer needed, the appetite becomes less
keen and more select in its choice, and digestion loses something of
the resistless power which generally distinguishes it in early youth.
Articles of food which were once digested with ease are now burdensome
to the stomach, and, if not altogether rejected, are disposed of with a
degree of labour and difficulty that was formerly unknown. Abstinence
also is now more easily supported.
When, however, the mode of life in mature age is active and laborious,
and the waste matter thrown out of the system is consequently
considerable, the appetite for food and the power of digesting it are
correspondingly strong; for in general it is only when the mode of life
is indolent and inactive, and the waste consequently small, that the
appetite and digestion are weak. So natural, indeed, is the connexion
between the two conditions, that _exercise_ is proverbially the
first thing we think of recommending to improve the appetite and the
tone of the digestive organs, when these are observed to be impaired;
and where positive disease does not exist, no other remedy is half so
effectual. But, as already noticed, exercise to be beneficial must be
of a description calculated to increase the activity of the secretions
and excretions; otherwise it cannot place the system in a condition to
require an abundant supply or excite vigorous digestion.
It is highly important to notice this natural relation between waste
and appetite, and between appetite and digestion; because, if it be
real, appetite must be the safest guide we can follow in determining
when and how much we ought to eat. It is true that in disease,
and amidst the factitious calls and wants of civilized life, its
suggestions are often perverted, and that hence we may err in blindly
following every thing which assumes its semblance. The conclusion to
be drawn from this, however, is, not that the sense of hunger will,
if trusted to, generally mislead us, but only that we must learn to
distinguish its true dictates before we can implicitly rely on its
guidance. If, when _fairly_ consulted, its dictates are found
to be erroneous, it will constitute the only known instance where
the Creator has failed in the attempt to fulfil his own design--an
assumption not only repugnant alike to feeling and to reason, but
in fact altogether gratuitous. For the apparent discrepancies which
occasionally present themselves between the wants of the system and the
dictates of appetite, are easily explicable on the more solid ground of
our own ignorance and inattention.
Many practical errors arise from overlooking the relation which
nutrition ought to bear to waste and growth. Thus, it is no uncommon
thing for young men who have experienced all the pleasures of a keen
appetite and easy digestion when growing rapidly or leading an active
life, to induce severe and protracted indigestion, by continuing, from
mere habit, to eat an equal quantity of food either when growth is
finished and the system no longer requires the same extensive supply,
or after a complete change from active to sedentary habits has greatly
diminished that waste which alone renders food necessary. This is, in
fact, one of the chief sources of the troublesome dyspeptic complaints
often met with among the youthful inhabitants of our larger cities and
colleges, and ought not to be lost sight of in the physical education
of the young.
The error, however, is unhappily not confined to the young, but extends
generally to all whose pursuits are of a sedentary nature. There are
numerous persons, especially in towns and among females, who, having
their time and employments entirely at their own disposal, carefully
avoid every thing which requires an effort of mind or body, and
pass their lives in a state of inaction entirely incompatible with
the healthy performance of the various animal functions. Having no
bodily exertion to excite waste, promote circulation, or stimulate
nutrition, they experience little keenness of appetite, have weak
powers of digestion, and require but a limited supply of food. If,
while inactive and expending little, such persons could be contented
to follow nature so far as not to provoke appetite by stimulants and
cookery, and to eat and drink only in proportion to the wants of the
system, they would fare comparatively well. But having no imperative
occupation and no enjoyment from active and useful exertion, their
time hangs heavily on their hands, and they are apt to have recourse
to eating as the only avenue to pleasure still open to them; and,
forgetful or ignorant of the relation subsisting between waste and
nutrition, they endeavour to renew, in the present indulgence of
appetite, the real enjoyment which its _legitimate_ gratification
afforded under different circumstances. Pursuing the pleasures of the
table with the same ardour as before, they eat and drink freely and
abundantly, and, instead of trying to acquire a healthy desire for food
and increased powers of digestion by exercise, they resort to tonics,
spices, wine, and other stimuli, which certainly excite for the moment,
but eventually aggravate the mischief by obscuring its progress and
extent. The natural result of this mode of proceeding is, that the
stomach becomes oppressed by excess of exertion--healthy appetite
gives way, and morbid craving takes its place--sickness, head-ach, and
bilious attacks, become frequent--the bowels are habitually disordered,
the feet cold, and the circulation irregular--and a state of bodily
weakness and mental irritability is induced, which constitutes a heavy
penalty for the previous indulgence. So far, however, is the true
cause of all these phenomena from being perceived even then, that a
cure is sought, not in a better regulated diet and regimen, but from
bitters to strengthen the stomach, laxatives to carry off the redundant
materials from the system, wine to overcome the sense of sinking, and
heavy lunches to satisfy the morbid craving which they only silence for
a little. Some, of course, suffer in a greater and others in a less
degree, according to peculiarities of constitution, mode of life, and
extent of indulgence; but daily experience will testify, that, in its
main features, the foregoing description is not over-charged, and that
victims to such dietetic errors are to be met with in every class of
society.
The fact of Nature having meant the inactive and indolent to eat and
drink less than the busy and laborious, is established not only by
the diminished appetite and impaired digestion of human beings who
lead a sedentary life, as contrasted with the keen relish and rapid
digestion usually attendant on active exertion in the open air, but on
a yet broader scale by the analogy of all other animals. In noticing
this relation, Dr Roget remarks that “the greater the energy with
which the more peculiarly animal functions of sensation and muscular
action are exercised, the greater must be the demand for nourishment,
in order to supply the expenditure of vital force created by these
exertions. Compared with the torpid and sluggish reptile, the active
and vivacious bird or quadruped requires and consumes a much larger
quantity of nutriment. The tortoise, the turtle, the toad, the frog,
and the chameleon, will indeed live for months without taking any
food.” “The rapidity of development,” he continues, “has also great
influence on the quantity of food which an animal requires. Thus the
caterpillar, which grows very quickly, and must repeatedly throw off
its integuments, during its continuance in the larva state, consumes a
vast quantity of food compared with the size of its body; and hence we
find it provided with a digestive apparatus of considerable size.”[9]
Hence, too, the greater demand for food in infancy and youth when
growth and activity are both at their height.
In thus insisting on regular bodily and mental activity as
indispensable to the enjoyment of a good appetite and sound digestion,
the attentive reader will not, I trust, be disposed to accuse me of
inconsistency because, when treating of muscular exercise in the
former volume,[10] I explained the bad effects, and inculcated the
impropriety, of indulging in any considerable exertion _immediately
before or after a full meal_. It is true, as there mentioned, that
exercise, either in excess or at an improper time, impairs the tone of
the stomach; but it is not on that account the less true that bodily
exertion when seasonably and properly practised, is the best promoter
of appetite and digestion which we possess; and it is only under
the latter conditions that I now speak of it as beneficial and even
indispensable to health.
In a work like the present, it is obviously impossible to fence round
every general proposition with the numerous limitations which an
unusual combination of circumstances, or a departure from the state of
health, might demand. And, even if possible, it would not be necessary,
as the laws of exercise have been so fully explained in the volume
alluded to, that their re-discussion here would unavoidably involve
much repetition from its pages. At the same time, some warning remark
may be required to prevent any risk of misconception, as it might
otherwise be plausibly argued, for example, that there can be no
such relation as I have alleged between waste and appetite, because
a European perspiring under a tropical sun incurs great waste, and
yet loses both appetite and digestive power. To render this a valid
exception, it must be shewn that the European is intended by Nature to
live in a tropical climate, and that the diet to which he accustoms
himself is that sanctioned by experience as the best adapted for his
constitution; because, if neither is the case, his condition under
such influences must necessarily be more or less closely allied to
the state of disease, and therefore beyond the sphere to which alone
my remarks are meant to apply. But even in that instance there is
less contradiction than might be imagined, for the waste of the
system being chiefly fluid, excites--not appetite, but its kindred
sensation--thirst, to repair the loss by an unusual demand for
refreshing liquids.
So true is it that the Creator has established a relation between
action and nutrition, that when we attempt for any length of time to
combine a full and nutritious diet with systematic inactivity, the
derangement of health which generally ensues gives ample proof of the
futility of struggling against His laws. Individuals, indeed, may be
met with, who, from some peculiarity of constitution, suffer less than
the generality of mankind from making the experiment; but even those
among them who escape best, generally owe their safety to the constant
use of medicine, or to a natural excess in some of the excretory
functions, such as perspiration or the urinary or alvine discharges,
by means of which the system is relieved much in the same way as by
active exercise; and hence the remark made by Hippocrates, that severe
perspirations arising during sleep without any other apparent cause
are a sure sign that too much nourishment is made use of. In others,
again, the day of reckoning is merely delayed, and there is habitually
present a state of repletion, which clogs the bodily functions, and
may lead to sudden death by some acute disease when the individual
is apparently in the highest health. I am acquainted with several
individuals of this description, who, in the absence of all bodily
exercise, are accustomed to live very fully,--to eat in the morning a
hearty breakfast, with eggs, fish, or flesh,--a good solid luncheon,
with wine or malt liquor, in the forenoon,--a most substantial dinner,
with dessert and several glasses of wine, and afterwards tea and wine
and water, in the evening,--and who nevertheless enjoy tolerably good
digestion. But this advantage is generally only temporary, and even
when permanent can scarcely be considered as a boon; because it is
gained at the direct expense either of a very full habit of body and an
unusual liability to abdominal congestion and all its attendant evils,
or of frequent and profuse perspirations, and severe attacks of bowel
complaint, endangering life; so that strictly considered such cases are
no exceptions to the general rule.
It is, then, no idle whim of the physician to insist on active exercise
as the best promoter of appetite and digestion. Exercise is, in fact,
the condition without which exhalation and excretion cannot go on
sufficiently fast to clear the system of materials previously taken
in; and where no waste is incurred, no need of a fresh supply, and
consequently, in a healthy state of the system, no natural appetite,
can exist. It is therefore not less unreasonable than vain for any one
to insist on possessing, at the same time, the incompatible enjoyments
of luxurious indolence and a vigorous appetite,--sound digestion of a
hearty meal, and general health of body; and no one who is aware of the
relation subsisting between waste and appetite can fail to perceive the
fact, and to wonder at the contrary notion having ever been entertained.
* * * * *
Among the operative part of the community we meet with innumerable
examples of an opposite condition of the system, where, from excess
of labour, a greater expenditure of energy and substance takes place
than what their deficient diet is able to repair. It is true that
the disproportion is generally not sufficient to cause that immediate
wasting which accompanies actual starvation, but its effects are
nevertheless very palpably manifest in the depressed buoyancy, early
old age, and shorter lives of the labouring classes. Few, indeed,
of those who are habitually subjected to considerable and continued
exertion survive their forty-fifth or fiftieth year. Exhausted at
length by the constant recurrence of their daily task and imperfect
nourishment, they die of premature decay long before attaining the
natural limit of human existence.
In those states of the system, again, such as fever, during the
continuance of which most of the secretions are vitiated, and that
of the gastric juice often entirely suppressed, and where food would
consequently be hurtful rather than advantageous, appetite is scarcely
felt, and loathing often occupies its place. But the moment that, by
the diminution of the disease, the secretions and exhalations begin
to return to their healthy state, and nutrition is resumed, appetite
begins to be again felt, and by-and-by becomes abundantly vigorous, in
order to restore the system to its former state. The utmost caution,
however, is still required in its gratification, as a premature
indulgence is almost certain again to stop the secretions and to
produce a relapse. Ignorance of this principle among the community
at large, and the consequent error of giving food when there is no
demand for it, and no gastric juice to digest it, often do more to
defeat the best laid plan of cure than the severity of the disease
itself. The sick man’s friends, in their anxiety to support his
strength, too frequently turn a deaf ear to every caution which is
suggested, and stealthily administer sustenance when the system does
not require it, and when it serves only to aggravate the danger and
increase the weakness of the patient. Since the first publication of
the preceding passage, I have seen a striking example of its truth.
The patient was gradually recovering from inflammation of the chest,
for the cure of which low diet was for a time indispensable. By way
of _supporting the diminished strength_, the relations began to
give prematurely and clandestinely, about double the quantity of food
which was prescribed. For twenty-four hours, an increase of strength
was felt accordingly; but very soon it passed into febrile excitement
with a quick pulse and _increased weakness_. A dangerous relapse
followed, and its cause was then found out. Abstinence was again
enforced and tartar emetic given to excite nausea. To the surprise of
the very injudicious friends, the excitement began almost immediately
to subside and the strength to improve where they had just seen it fast
giving way under a full diet.
Appetite, it ought to be observed, may, like other sensations, be
educated or trained to considerable deviations from the ordinary
standard of quantity and quality--and this obviously for the purpose
of enabling man to live in different climates and under different
circumstances, and avoid being fixed down to one spot and to one
occupation. In civilized life, however, we are accustomed to take undue
advantage of this capability, by training the appetite to desire a
greater quantity of food than what the wants of the system require,
and stimulating its cravings by a system of cookery little in harmony
with the intentions of Nature. But this is evidently an abuse, and
no argument whatever against the sufficiency of its _natural_
indications to lead us right.
But the most common source of the errors into which we are apt to
fall in taking appetite as our only guide, is unquestionably the
_confounding of appetite with taste_, and continuing to eat for
the gratification of the latter long after the former is satisfied;
just as the dog already mentioned ate till the œsophagus was distended,
although it did not experience the slightest sensation of hunger.[11]
In fact, the whole science of a skilful cook is expended in producing
this _willing_ mistake on our part; and he is considered decidedly
the best _artiste_ whose dishes shall recommend themselves most
irresistibly to the callous palate of the gourmand, and excite on
it such a sensation as shall at least remind him of the enviable
excellence of a natural appetite. If we were willing to limit the
office of taste to its proper sphere and to cease eating when appetite
expressed content, indigestion would be a much rarer occurrence in
civilized communities than it is observed to be.
Viewed, then, in its proper light, appetite is to be regarded as kindly
implanted in our nature for the express end of proportioning the supply
of nourishment to the wants of the system; and if ever it misleads us,
the fault is not in its unfitness for its object, but in the artificial
training which it receives at our own hands, and in our habitual
neglect of its dictates. When we attend to its real indications, we eat
moderately, and at such intervals of time as the previous exercise and
other circumstances render necessary; and in so doing, we reap a reward
in the daily enjoyment of the pleasure which attends the gratification
of healthy appetite. But if we err, either by neglecting the timely
warning which it gives, or by eating more than the system requires,
mischief is sure to follow. In the former case, waste continues to
make progress till the body becomes exhausted; and in almost exact
proportion do the cravings of appetite become more and more intense,
till they pass into those of uncontrollable _hunger_, which
overthrows all obstacles, and seeks gratification at the risk of
life itself. In the latter case, indigestion, gloomy depression, and
repletion with its concomitant evils, make their appearance, and either
embitter or cut short existence.
Mischief sometimes arises also from people not being sufficiently aware
that, in common with other sensations, appetite may be so far deranged
by disease as to give very incorrect and unnatural indications. It
often happens, for example, that a patient shivers and complains of
cold, when we know by the thermometer that the heat of the skin is
really above instead of below the natural standard. In like manner,
in some morbid states of the nervous system a craving is often felt
which impels the patient to eat, but which is not true hunger; and
here food, if taken, is digested with great difficulty. Occasionally,
on the other hand, no desire for food is experienced when the system
really needs it, and when it would be digested with ease if introduced
into the stomach. Esquirol alludes to cases of this description, and
I have met with similar examples. Voison also mentions, that, in the
Hospital of Incurables in Paris, there are some idiots so low in the
scale of intelligence, as to make no attempt to take the food which
is placed before them, although they eat and digest readily when fed
by others. Sometimes, again, appetite is depraved in quality, and the
patient desiderates the most nauseous and repulsive kinds of food,
such as earth, chalk, coals, or excrement. There are states, too, in
which the appetite is prodigiously increased, and the patient consumes
incredible quantities of food,--which, however, are very imperfectly
digested. Charles Domery, for instance, when a French prisoner at
Liverpool, consumed, in one day, four pounds of cow’s udder and ten
pounds of raw beef, with two pounds of tallow candles and five bottles
of porter; and although allowed the daily rations of ten men he was
still not satisfied. Baron Percy speaks of another man, who ate
twenty-four pounds of beef in as many hours, and thought nothing of
swallowing a dinner prepared for fifteen German boors. I once attended
a patient who was afflicted with a similar inordinate craving, and
whose only pleasure was in eating. In such cases no restraint except
actual coercion is sufficient to prevent indulgence; but the craving
itself is as much the product of disease as the shivering in the
beginning of fever, and can no more be removed by reasoning than the
sensation of cold can be removed by telling a patient that his skin is
thermometrically warm. But these, being cases of disease, do not in any
degree militate against the accuracy of the exposition above given of
the healthy uses of appetite.
The general considerations which I have just submitted to the reader
on the subject of appetite for food, apply so closely to the sensation
of _Thirst_, that to enter into any detail concerning the latter
would be little else but to be guilty of repetition. I shall therefore
limit myself to a very few remarks.
Thirst is generally said to have its seat in the back of the mouth
and throat; but the condition of these parts is merely a local
accompaniment of a want experienced by the whole frame, and perceived
by the nervous system. Local applications, accordingly, go but a short
way in giving relief, while the introduction of fluids by any other
channel--by immersion in a bath, by injection into the veins, or
through an external opening into the stomach--is sufficient to quench
thirst without the liquid ever touching the throat. The affection of
that part, therefore, is merely a result of the state of the system,
and not itself the cause of thirst.
Thirst, or a desire for liquids, is experienced in its greatest
intensity when the secretion and exhalation of the animal fluids is
most active; and it is consequently most urgent in summer, in warm
climates, and in persons engaged in severe exertion, particularly
if exposed at the same time to a heated atmosphere. Blacksmiths,
glass-blowers, engineers, and others, whose employment exposes them
to the heat of furnaces, and in whom perspiration is excessive, are
accordingly almost constantly under the influence of thirst; whereas
those who are employed in professions requiring only moderate exertion
in a temperate atmosphere, and in whom the fluid secretions are very
moderate, rarely experience the sensation in an urgent degree. For the
same reason great loss of blood induces excessive and intolerable
thirst; and hence, in the battle-field, the generous self-denial of him
who passed the cup to his wounded neighbour, without stopping even to
moisten his own lips, cannot be too highly appreciated.
Thirst varies in intensity also according to the nature of the food. If
the diet be hot and stimulating, such as results from a free admixture
of spices or salt, the desire for drink is greatly increased. The same
thing happens if the food be of a dry and solid nature. The purpose
of the increased thirst in the former circumstances is manifestly to
dilute and diminish the excess of stimulant, and thereby prevent the
injury which it would otherwise inflict. The same principle explains
the thirst experienced by those who drink too much wine. In instances
of this kind I have heard great thirst in the evening and during the
night complained of as habitual, without the person even suspecting
that it was owing to the wine; and yet, on abstaining from the latter,
the thirst very soon disappeared.
Continued thirst, it is well known, is much more intolerable than
continued hunger. The mass of circulating fluid in the body is very
great, and, as the various excretions consist chiefly of fluid matter,
it necessarily happens that when these have been eliminated for a
considerable time without any liquid being received into the system,
the proportion of solid matter in the body becomes unduly large. The
blood, consequently, becomes thicker and changed in quality, and much
more irritating than it is in its natural state. The craving of thirst
is thus generally rendered more urgent and overpowering than that of
hunger.
In Asiatic Cholera, the watery portion of the blood, on which its
fluidity depends, is drained off with frightful rapidity; and the
result is, in the first place, an almost complete stoppage of the
circulation, and, in the second, a constant craving for drink to supply
the place of the lost serum, which consists chiefly of water holding
some of the alkaline salts in solution. This circumstance explains in
some degree the extraordinary effects which have been produced, even
in the worst stages of the disease when life seemed almost extinct, by
injecting large quantities of saline solutions into the veins. Patients
apparently on the verge of existence, cold, pulseless, and inanimate,
have in the course of a few minutes been enabled by this means to
sit up in bed, and to exhibit all the signs of restored strength and
health. The effect, it is true, was rarely permanent, but for the time
it was so wonderful as often to look like restoration from the dead.[12]
Fluids taken into the stomach, it is proper to observe, are not
subjected to the slow process of digestion, but are absorbed
_directly_ into the system; so that, when we take a moderate
draught, the whole of it is imbibed from the stomach in a very few
minutes. Keeping in view this fact, and the above striking illustration
of the influence of the condition of the blood upon the body at
large, it becomes easy to conceive why, in a state of exhaustion from
abstinence, drink should be more speedily restorative and refreshing
than food.
Thirst, like appetite for food, is intended to direct us when and in
what quantity we ought to drink; and so long as we lead a life of
ordinary health and activity, and confine ourselves to the fluids with
which nature provides us, there is little chance of our going far wrong
by listening to its calls. But when we become indolent and dyspeptic,
or resort to the use of fermented and stimulating liquors, which excite
a thirst not recognised by Nature, the principle ceases to apply. At
present, however, my observations refer entirely to such simple drinks
as water, and to the state of health; and I shall touch upon other
liquids when treating of diet in a subsequent part of the volume.
Many persons without experiencing any real thirst, habitually indulge
in potations of water or beer at all hours of the day, and to an
extraordinary extent, and feel unhappy when suddenly restricted in the
indulgence. But this temporary discomfort ought not to be considered
as indicating that these potations are really necessary, because the
same result happens in the analogous instances of smoking or snuffing.
All three are abuses and perversions of Nature, and the uneasiness
attending the sudden cessation of the beer or water drinking is no more
a proof of either fluid being required, than that consequent on giving
up cigar smoking is an indication that Nature designed the lungs for
the reception of the impure effluvia of the tobacco leaf instead of the
fresh breezes of heaven.
CHAPTER III.
MASTICATION, INSALIVATION, AND DEGLUTITION.
Mastication--The teeth--Teeth, being adapted to the
kind of food, vary at different ages and in different
animals--Teeth classed and described--Vitality of teeth
and its advantages--Causes of disease in teeth--Means of
protection--Insalivation and its uses--Gratification of taste in
mastication--Deglutition.
Having seen that a regular supply of nourishment is carefully insured
by the constantly returning impulses of Appetite, we come next
to examine the mode in which the food is prepared for becoming a
constituent part of the animal machine, and endowed with the properties
of life.
The first important step in the complicated process of digestion,
is that by which the food, after being received into the mouth,
is mixed with the saliva and broken down till it becomes of a
uniform pulpy consistence, fit for being easily swallowed and acted
upon by the gastric juice on its arrival in the stomach. The term
_mastication_ or _chewing_ is used to denote this operation;
and the chief instruments by which it is performed are the teeth, the
jaws, the muscles which move the jaws, the tongue, and the salivary
glands. On each of these we shall offer a few observations.
[Illustration]
The TEETH vary a good deal according to the kind of food on which the
animal is destined to live; but in man and the higher orders of animals
they may be divided into three distinct groups:--_1st_, The _incisor_
or _cutting_ teeth, being the eight broad and flat teeth with a sharp
cutting edge seen in front of the upper and lower jaws, and marked I in
the subjoined wood-cut, which represents one-half of the lower jaw, and
consequently only one-fourth of the whole number of teeth. Thus we find
only two incisors marked in the wood-cut, although there are eight of
them in all, viz. two more are on the other side of the lower jaw, and
four corresponding ones in the upper. _2d_, The _cuspidati_, _canine_,
or _dog_ teeth, being the sharp-pointed roundish-bodied teeth, four in
number, one, C, in contact with each of the outer incisor teeth, and
called _canine_ from being large in the dog and carnivorous animals,
and used by them for the purpose of _seizing_ and _tearing_ their food;
and, _3d_, The _molares_ or _grinders_, B G, twenty in number situated
at the back part of the jaw, and so called from their office being
to grind or bruise the food subjected to their action.[13] The term
_grinders_, however, is sometimes restricted to the three back teeth on
each side, marked G, and seen to have double roots and a broad grinding
surface; and the two, B, intervening between them and the _cuspidati_
are styled _bicuspidati_ or _double-speared_, from bearing a greater
resemblance to a double-headed canine tooth than to the other grinders.
The teeth are modified in different animals to suit their habits of
life. In herbivorous animals, the canine teeth, for which they have no
use, are comparatively undeveloped; whereas in carnivorous animals,
which tear their prey in pieces, the canine teeth are large, powerful,
and pointed, and the incisors comparatively small. In these animals
they constitute what are properly called the _tusks_, and in some
species they are of a truly formidable character. The molar or grinding
teeth differ in like manner according to the nature of the food. In
herbivorous and granivorous animals they are large and powerful, and
to increase their efficiency the lower jaw admits of considerable
lateral motion in a horizontal direction; whereas, in carnivorous
animals, it admits of motion only upwards and downwards, as in opening
and shutting the mouth. The lateral grinding motion is very evident
in _ruminating_ animals, such as the cow, which, after having
filled its stomach with provender, is generally seen to lie down and
_ruminate_, or _chew the cud_ as it is called--the rumination
consisting in bringing up small masses of herbage from the stomach,
and submitting them to a thorough mastication or grinding between its
molar teeth before being again swallowed and digested.
From this relation between the food and the organs of mastication,
naturalists can tell with certainty, by simply inspecting the teeth, on
what kind of food the animal to which they belong is intended to live;
and as the teeth of man partake of the characters of those of both
herbivorous and carnivorous animals, there cannot be a doubt that his
diet was intended to be of a mixed kind, not confined exclusively to
either the vegetable or the animal kingdom.
Hard and resisting as the teeth appear, they must still be regarded as
living structures. Anatomically speaking, each tooth is divided into
three parts: the _fang_ or _root_, implanted in the socket of
the jaw-bone; the _neck_, or portion encircled by the gum; and the
white _crown_, appearing above the gum, and covered with enamel.
The root of each tooth is perforated longitudinally by a small canal,
through which the bloodvessels and nerve are admitted to its central
parts. From these bloodvessels the tooth derives its nourishment when
growing; but they afterwards almost entirely disappear. From the nerve
it derives that sensibility which makes us instantly aware of the
contact of bodies either too hot or too cold with the teeth; and which,
when the nerve is diseased, gives rise to the racking pain of toothach.
So effectually is life maintained in the teeth by this provision of
vessels and nerves, that a tooth newly extracted from the socket of
a young animal, and implanted in the fleshy comb of a cock, has been
found to adhere and retain its vitality; and, in like manner, if, in
early life, a tooth extracted by accident be immediately replaced in
its socket, it will generally adhere and live.
The visible part or crown of the tooth is covered with a very hard
white ivory-looking substance called _enamel_, which serves to
prevent it from being worn down by friction, and into which neither
bloodvessels nor nerves have been observed to penetrate. Owing to this
structure, the tooth can be safely exposed without sustaining damage--a
privilege on which most persons will be disposed to place a higher
value after having experienced the pains consequent upon injury of the
nerve from a portion of the enamel being broken off.
An obvious advantage attending the vitality of the teeth is, that it
enables them to accommodate themselves to the growth of the jaw and
the rest of the system at the different periods of life. In early
infancy, when the human being is designed to live exclusively on his
mother’s milk, which of course requires no mastication and consequently
no teeth, the latter are still imperfectly formed and entirely hidden
in the jaw: it is only at the end of some months that the front or
cutting teeth begin to appear; and the whole set of _milk_,
_deciduous_, or _falling-out_ teeth, twenty in number, is not
completed till about or after the third year. In the course of three or
four years more, however, growth has advanced so far that the first set
of teeth no longer fill the jaw; and they soon begin to be displaced by
the second or permanent set, the gradual development of which commences
at that period of life, and is not finished till the appearance of the
last four grinders or _wisdom-teeth_, about the age of maturity.
It is a curious fact that the infant is born with the rudiments of both
sets of teeth in the jaw at the same time, although neither makes its
appearance till long after birth. The permanent teeth lie in a line
under the milk-teeth, and it is from their growth causing the gradual
absorption of the roots of the first teeth that the latter no longer
retain their hold of the jaw, but drop out as soon as the others are
ready to protrude. In the preceding wood-cut, the situation of the
permanent teeth before they emerge from the jaw is rudely represented
at A, where the outer surface of the jaw-bone has been removed on
purpose, to shew the appearance of the roots. But nothing of this kind
is to be found in the adult jaw, the parts marked A being inserted in
the plate merely to illustrate what was once the position which the
permanent teeth occupied.
The changes in the condition of the teeth, it may be remarked in
passing, indicate clearly what species of food nature has intended
for us at different ages. In early infancy, when no teeth exist, the
mother’s milk is the only nutriment required; and in proportion as
the teeth begin to appear, a small addition of soft farinaceous food
prepared with milk may be made with propriety and gradually increased.
But it is impossible to look at the small jaw, moderate muscle, and
imperfect teeth of early life, without perceiving that only the mildest
kinds and forms of animal food are yet admissible, and that the diet
ought to consist essentially of soft and unirritating materials. It is
not till the permanent teeth have appeared, that a full proportion of
the ordinary kinds of butcher-meat becomes either beneficial or safe.
The teeth, being living parts and at the same time endowed with a
mechanical function, are liable to injury in both capacities. Being
composed chiefly of earthy matter, such as phosphate and carbonate
of lime, the contact of strong acids decomposes their substance, and
leads to their rapid decay. Hence the whiteness produced by acid
tooth-powders and washes is not less deceitful than ruinous in its
consequences; and hence also great caution is necessary in swallowing
the acid drops frequently prescribed by the physician, which ought
never to be allowed to come into contact with the teeth.
The teeth being constantly moistened with saliva, have a tendency to
become incrusted with the tartar or earthy matter which it contains
in solution, and which is separated from it partly by the evaporation
of the more fluid constituents in breathing, and partly by chemical
decomposition. As this incrustation not only destroys the beauty of
the teeth, but also promotes their decay, it becomes an object of care
to remove it as soon as it is formed; and the most effectual mode of
doing so is to brush the teeth regularly twice a day--especially in
the morning, when the quantity is greatest--with a brush dipped in
soft water, till every particle is removed. The addition of any soft
impalpable powder will assist in the effect; but nothing capable of
acting chemically on the teeth, or of injuring them by friction, ought
ever to be resorted to. Washing the mouth after every meal is also a
good preservative.[14]
When the teeth are not used for a time, and when digestion is impaired,
the quantity of tartar which accumulates on them is very great. Hence
they are always most incrusted in the morning, and in fevers and other
affections where no food is taken, and the stomach is at the same
time disordered. I have seen one instance in which a thick crust of
tartar was removed by a dentist in the belief of its being a diseased
tooth--the tooth itself on which it was formed being left in the jaw
perfectly sound.
When the tartar is not duly removed, its presence injures the
teeth, irritates the gums, and generally leads, sooner or later,
to considerable suffering. The regular washing and brushing above
mentioned ought, therefore, to be sedulously practised at every period
of life, and taught as a duty to the young. When digestion is very
vigorous, the health good, and the diet plain and containing a full
proportion of vegetable matter, the deposition of tartar seems to
be diminished, and the teeth to be naturally of a purer white. Many
rustics and savages thus possess teeth which would be envied in a town.
When digestion is impaired, and acidity prevails in the stomach, the
mucous secretions in the mouth also become altered in character, and by
their incessant contact injure and even destroy the teeth. From this
cause we often see the teeth in young people in a state of complete
decay. They are in reality the subjects of chemical decomposition,
and eaten away by the morbid secretions of the mouth; and hence, in
such cases, we generally find the individual complaining of heat and
soreness of the tongue, gums, and mouth, and occasionally of the teeth
being “set on edge.”
Considered as _living_ parts, the teeth require some additional
care. In that capacity they are exceedingly apt to suffer from sudden
changes of temperature. Being from their solidity rapid conductors
of heat, their internal nerve speedily becomes affected by the
alternations of temperature to which they are daily exposed, both in
taking food and in the change from a warm to a cold atmosphere. It is
a not uncommon practice, for example, to take a glass of cold wine or
water immediately after finishing a plateful of very hot soup; and it
is quite usual to take tea and coffee and every kind of meat as hot
as they can possibly be swallowed--than which practices it would be
difficult to imagine any thing more hurtful to the teeth.
For the same reason, in going out at night from a warm room to the
coil air, it is desirable to protect the teeth from the influence of
the sudden change, by breathing through two or three folds of a silk
handkerchief, or through a woollen _comforter_. When the teeth
and lower part of the face are left exposed in such circumstances,
rheumatism and toothach not unfrequently ensue from the direct
impression of the cold air upon parts rendered more susceptible by the
preceding heat.
The great source of injury to the teeth, however, both in childhood
and in mature age, is disordered digestion. If the health be good, and
the stomach perform its functions with vigour, the teeth will resist
much exposure without sustaining injury. But if these conditions fail,
they will rarely continue long unscathed.
It is almost always from the latter cause that, in infancy, teething so
often gives rise to serious constitutional disorder.
* * * * *
Something more, however, than the mere action of the teeth and jaws is
required to prepare the morsel for being swallowed. If we take a bit of
dry biscuit or mealy potato into the mouth, and attempt to masticate
it, we encounter at first no small difficulty from the stiffness and
resistance of the dry mass, and feel instinctively that it would be
in vain to attempt to swallow it, until moistened either by continued
mastication or by the admixture of fluid from without. In ordinary
states of the system, accordingly, a fluid called _saliva_ or
_spittle_ is copiously secreted and poured into the mouth for
this very purpose; and the process by which its due admixture with the
contents of the mouth is accomplished is called the _insalivation_
of the food.
To provide this necessary fluid, and to connect its supply directly
with the process of mastication to which it is subservient,
several glands for its secretion have been placed in the immediate
neighbourhood of the mouth and jaws, in such a way that the latter
cannot be opened and shut without affording them a stimulus, and still
farther increasing the secretion which the presence of the morsel is
itself sufficient to begin. From this arrangement it follows, that
the more perfectly mastication is performed, the more thoroughly does
the morsel become impregnated with the salivary fluid, and the better
fitted is it rendered for subsequent deglutition and digestion.
The apparatus of mastication varies according to the kind of food on
which the animal is destined to live; but in the higher orders of
animals, it consists essentially of the parts already mentioned. In
some animals, however, which live on soft gelatinous food--as the
whale--no teeth are to be found, because their peculiar power is not
required. In others--as the granivorous or grain-eating birds--the
grinding or _triturating_ process is effected not in the mouth but
in the gizzard, where the food (mixed with gravel, which the animal
is instinctively impelled to swallow for the purpose) is effectually
bruised and softened down by the strong muscles which constitute the
greater part of its substance. In these instances, the gravel is the
grinding instrument, and without its presence digestion cannot be
carried on any more than it could in man without the agency of teeth.
The degree of mastication required varies also according to the mode
of life of the animal, and the digestibility of its food. Animal food,
for example, being easy of digestion, requires less mastication than
vegetable food, which is more difficult. This is so much the case, that
most animals which live on fresh vegetable matter spend half their
waking hours in _ruminating_ or re-masticating the food, which
they have already cropped and stored up for the purpose in one of their
four stomachs. To this necessary act in them, Providence seems to have
attached a high degree of gratification, for the very purpose of
insuring its regular performance.
Man, being naturally omnivorous, or adapted for the digestion of both
animal and vegetable substances, holds, as it were, an intermediate
place in regard to the rapidity of mastication. He is neither obliged
to ruminate like the cow, nor can he beneficially bolt his food with
the rapidity displayed by birds of prey. His object is merely to reduce
the alimentary mass to a soft and pulpy consistence, and digestion is
promoted or retarded in exact proportion as he approaches or falls
short of this point. Hasty mastication is consequently injurious,
because it prevents the food from being sufficiently broken down and
impregnated with saliva; and the more uncommon error of protracted
mastication is also injurious, owing to the undue dilution which the
mass sustains from the overflow of the salivary secretion.
Due mastication being thus essential to healthy digestion, the
Creator, as if to insure its being adequately performed, has kindly
so arranged, that the very act of mastication should lead to the
gratification of taste--the mouth being the seat of that sensation.
That this gratification of taste was intended, becomes obvious when
we reflect that, even in eating, Nature makes it our interest to give
attention to the process in which we are for the time engaged. It
is well known, for example, that when food is presented to a hungry
man, whose mind is concentrated on the indulgence of his appetite,
the saliva begins to flow unbidden, and what he eats is consumed
with a peculiar relish and is easily digested. Whereas, if food be
presented to an individual who has fasted equally long, but whose
soul is absorbed in some great undertaking or deep emotion, and who
is consequently insensible to the gratification of taste, it will be
swallowed almost without mastication, and without sufficient admixture
with the saliva--now deficient in quantity--and therefore lie on the
stomach for hours unchanged. In this point of view the peculiarly
English custom of reading the newspapers or magazines _during_
breakfast is more hurtful than one would suppose; and many dyspeptics
have been surprised at the benefit resulting from its discontinuance.
However, therefore, philosophy and morality condemn the _undue_
cultivation of our bodily appetites, it cannot be denied that a certain
degree of attention to taste, and to the pleasures of appetite, is both
reasonable and beneficial; and it is only when these are abused that we
oppose the intentions of Nature.
From the existence of this intentional relation between mastication
and the salivary secretion, the latter is always most copious in those
creatures whose food requires continued mastication. In ruminating
animals, accordingly, the salivary glands are numerous and of great
size, while they are at the same time so situated that the play of the
muscles in the act of rumination communicates to them a proportionate
stimulus. In those, again, which do not masticate at all, but swallow
their food entire, there is scarcely any salivary secretion, and the
glands appropriated to it are very small. Birds, and many fishes and
reptiles, belong to the latter class.
From the foregoing explanation of the object and conditions of
mastication, the reason will be apparent why _fluids_ do not
require to undergo that process, and also why dry mealy substances
stand in need of protracted chewing before they can be easily
swallowed. When hot spicy food is taken into the mouth, the secretion
of saliva is immensely increased, obviously for the purpose of diluting
the excess of stimulant before it shall be allowed to reach the
stomach. But when the food is of a mild and unirritating quality, much
dilution is unnecessary, and the secretion is accordingly moderate.
The chief purpose of mastication, then, is evidently the minute
division of the aliment, so as to admit of its being easily acted upon
by the gastric juice when received into the stomach. Dr Beaumont,
however, seems to me to go too far in inferring, that “if the
_materia alimentaria_ could be introduced into the stomach in a
finely divided state, the operations of mastication, insalivation, and
deglutition, would not be necessary.” It would require a more extensive
range of experiments than that which he has made, to prove that
“aliment is as well digested and assimilated, and allays the sensation
of hunger as perfectly, when introduced directly into the stomach
(through an opening in the side) in a proper state of division, as when
the usual previous steps have been taken.”[15] It is quite true that
mastication and deglutition are chiefly mechanical processes; but it is
difficult to believe that so much care would have been taken to provide
a proper supply of fluid of a constant and _peculiar_ character
like saliva, if water were capable of answering the purpose as well,
and if saliva were useful _only_ in lubricating the food.
There subsists, moreover, between the sense of taste and the power
of digestion a certain relation, which renders it more than probable
that the active gratification of the former during mastication, is
favourable to the production and flow of nervous energy towards
the stomach, and consequently in so far conducive to the healthy
performance of digestion that even in that point of view insalivation
could not easily be dispensed with. Dr Beaumont’s experiments, however,
abundantly demonstrate that Montègre, and those who, along with him,
consider the saliva as the _principal_ agent in digestion, have
not a shadow of foundation for their opinion.
When unmasticated food is introduced into the stomach, the gastric
juice acts only upon its surface, and changes of a purely chemical
nature sometimes commence in its substance before its digestion can
be effected. Hence often arise, especially in children, those pains
and troubles, that nausea and acidity, consequent on the continued
presence of undigested aliment in the stomach. By a peculiarity of
constitution, however, the stomach will not long retain food which
it cannot dissolve. After a number of hours,--varying, according to
the state of health, from one or two to ten, or even twenty,--it is
either rejected by vomiting, or transmitted unchanged to the intestine,
where its presence irritates and gives rise to colic, flatulence,
bowel-complaints, and, in delicate children, not unfrequently to
convulsions. Hence another proof of the importance of slow and
deliberate mastication.
* * * * *
As soon as the morsel has been thoroughly masticated and impregnated
with saliva, it is ready for transmission to the stomach. To this part
of the process the term _deglutition_ or _swallowing_ is
applied.
Immediately at the back part of the mouth several passages present
themselves, leading in different directions--one upwards and forwards
into the nose, another downwards and in front into the windpipe, and
a third downwards and behind into the _œsophagus_, _gullet_
or _meat-pipe_ and stomach. The last is the passage taken by the
food, and the violent coughing and occasional suffocation induced when
it accidentally passes into the windpipe, are but a specimen of the
serious evils which would be continually occurring if some provision
were not made to obviate the danger, while the rarity with which such
accidents actually happen, proves the almost unfailing efficacy of that
which has been devised.
The passage of the food into the nostrils is prevented by the
interposition of a moveable fleshy curtain or valve hanging down from
the palate, and visible at the back part of the mouth; this, in the act
of swallowing, is stretched backwards so as to extend to the back part
of the throat, and thus entirely shut up the opening into the nostrils.
The passage into the windpipe, again, is protected by a cartilaginous
lid or covering called _epiglottis_ (from επι, _epi_, upon,
and γλωττις, _glottis_, the tongue), which projects backwards from
the root of the tongue, and conducts the morsel over the _glottis_
or opening of the windpipe. The epiglottis, however, is greatly
assisted in this operation by that rising upwards and forwards of the
gullet and windpipe to meet the morsel, of which we are conscious, and
which can be felt by the hand in the act of swallowing, and the effect
of which is in some degree to hide the glottis under the backward
projection of the root of the tongue, and allow the morsel to drop past
it into the gullet.
Once fairly in the gullet, the course of the food into the stomach
is easy enough. The gullet is simply a round tube, made up of two
rows of muscular or fleshy fibres, the one longitudinal and the
other transverse and circular, with a soft moist lining membrane
to facilitate the transmission of its contents. When the morsel is
introduced, its upper part contracts involuntarily, and pushes the mass
downwards; the portion now reached contracts in its turn, and propels
it farther; and so on in succession till it arrives at the stomach.
_Deglutition_ or _swallowing_ is thus a more complicated
operation than at first sight it appears to be. On looking at any
person eating, one is apt to think that the morsel passes along the
gullet into the stomach by its own weight; but we speedily perceive the
error, when we recollect that, in the horse and the cow for example,
the mouth is on a level with the ground when feeding, or drinking, and
that the morsel or water is consequently propelled upwards into the
stomach against its own gravity. It is well known also, and often made
a matter of public exhibition, that a man can swallow even liquids when
standing on the crown of his head, with the natural position of the
stomach reversed.
Deglutition is easier and quicker when the appetite is keen, and
the alimentary bolus or morsel is moist and properly softened. It
is slow and difficult when the morsel is dry and mealy, and the
appetite nauseated. In vomiting, the action of the muscular fibres
is _inverted_, or proceeds from the lower end of the gullet
towards the mouth; and hence the object is carried upwards instead of
downwards, as in the natural order.
CHAPTER IV.
ORGANS OF DIGESTION--THE STOMACH--THE GASTRIC JUICE.
Surprising power of digestion--Variety of sources of
food--All structures, however different, formed from the same
blood--General view of digestion, chymification, chylification,
sanguification, nutrition--The stomach in polypes, in
quadrupeds, and in man--Its position, size, and complexity, in
different animals--Its structure; its peritoneal, muscular, and
villous coats; and uses of each--Its nerves and bloodvessels,
their nature, origins, and uses--The former the medium of
communication between the brain and stomach--Their relation
to undigested food--Animals not conscious of what goes on in
the stomach--Advantages of this arrangement--The gastric juice
the grand agent in digestion--Its origin and nature--Singular
case of gunshot wound making a permanent opening into the
stomach--Instructive experiments made by Dr Beaumont--Important
results.
If, in the whole animal economy, where all is admirable, there be one
operation which on reflection appears more wonderful than another, and
which evinces in a higher degree the prodigious resources and power of
the Creator in fashioning every thing to His own will, it is perhaps
that by which the same kind of nutriment is extracted from the most
opposite varieties of food consumed by living beings. For, singular
as it may appear, recent researches tend to establish the fact, that,
even in animals differing so widely in their aliment as the herbivorous
and carnivorous quadrupeds, the ultimate products of digestion in
both--the chyle and the blood--are _identical_ in composition, in
so far at least as can be determined by their chemical analysis.[16]
Remarkable, however, as this uniformity of result undoubtedly is,
it becomes still more striking when we contemplate the variety of
sources from which food is derived for the support of animal life.
To use the words of an able writer already quoted, “There is no part
of the organized structure of an animal or vegetable, however dense
its texture or acrid its qualities, that may not, under certain
circumstances, become the food of some species of insect, or contribute
in some mode to the support of animal life. The more succulent parts
of plants, such as the leaves or softer stems, are the principal
sources of nourishment to the greater number of larger quadrupeds, to
multitudes of insects, as well as to numerous tribes of other animals.
Some plants are more particularly assigned as the appropriate nutriment
of particular species, which would perish if these ceased to grow:
thus the silk-worm subsists almost exclusively upon the leaves of the
mulberry-tree; and many species of caterpillars are attached each to a
particular plant, which they prefer to all others. There are at least
fifty different species of insects that feed upon the common nettle;
and plants of which the juices are most acrid and poisonous to the
generality of animals, such as euphorbium, henbane, and nightshade,
afford a wholesome and delicious food to others.”[17] Nor are the
precision and accuracy with which the same fluid--the blood--affords
to every structure of the body the precise species of nourishment or
secretion which its elementary composition requires, however different
each may be from the rest in chemical qualities, less admirable and
extraordinary than its own original formation from such a variety of
materials. To bone, the blood furnishes the elements of bone with
unerring accuracy; to muscle the same blood furnishes the elements of
muscle,--to nerves the elements of nerve,--to skin the elements of
skin,--and to vessels the elements of vessels;--and yet, while each of
these differs somewhat in composition from the others, the constituent
elements of the blood by which they are furnished are everywhere the
same.
Similar phenomena, indeed, occur in the vegetable world; but this,
instead of diminishing our wonder, tends rather to augment it. The
same elements, extracted from the same soil, are converted into every
variety of vegetable product--into leaves of every shade of green,
flowers of every form and tint, and juices of every quality, from
the deadly poison up to bland and life-supporting milk. Nay, even in
the same plant--as in the poppy--we sometimes find the seeds and the
capsule which covers them endowed with the most opposite properties.
It would be very interesting to discover by what resources Nature
thus effects the production of the same kind of nutritive fluid or
_chyle_, from so great a variety of substances, and apportions to
every part the precise elements of which it stands in need; but it is
doubtful whether the human faculties were ever designed to penetrate so
far into the modes of vital action, and, in the mean time, it will be
better for us to confine our attention to that branch of the inquiry
which we can easily comprehend, and which bears a direct reference to
our own welfare. We know already that certain organs are concerned in
the processes above mentioned, and that these organs act under the
regulation of certain general laws. If we make ourselves acquainted
with, and carefully fulfil, these laws, we reap a rich reward in the
enjoyment of sound and vigorous digestion. Whereas, if, either from
ignorance or from carelessness, we neglect their fulfilment, we bring
upon ourselves a severe punishment in the form of dyspeptic or nervous
disease. Assuredly, then, alternatives like these ought to excite some
desire for information in the minds even of the most indifferent.
* * * * *
Before, however, commencing a description of the organs concerned in
digestion, it will be useful to take a general view of the different
stages of preparation through which the food passes, between its
reception into the stomach and its _assimilation_, or ultimate
conversion into a constituent part of the animal body, and becoming
endowed with the properties of life. The reader will thus be better
enabled to understand the meaning of various terms and expressions, the
frequent use of which it is almost impossible to avoid, even in the
beginning of our exposition.
When the food is received into the stomach, it is there subjected
to the action of a solvent fluid, called the _gastric_ or _stomach
juice_ (from γαστηξ, _gaster_, stomach), by which it is gradually
converted into a soft greyish and pultaceous mass, called _chyme_,
(from χυμος, _chymos_, humour or juice); whence the process is called
_chymification_, or _chyme-making_. The chyme, as fast as it is formed,
is expelled by the contractile power of the stomach into the duodenum
(from _duodenus_, consisting of twelve, because it is supposed to be
about twelve inches long), or first portion of the intestines. It
there meets with the _bile_ from the liver, and with the _pancreatic
juice_, which very much resembles the saliva, from the _pancreas_ or
_sweet bread_ (πας, _pas_, all, and κρεας, _kreas_, flesh, it being
of a fleshy consistence), a large gland which lies across the spine a
little below the stomach, and is marked P in the wood-cut given in the
chapter on Chylification. By the action of these two fluids, the chyme
is converted into two distinct portions,--a milky white fluid named
_chyle_ (from χυλος, _chylos_, chyle), and a thick yellow residue.
This process is called _chylification_ or _chyle-making_. The chyle is
then sucked in by absorbent vessels, extensively ramified on the inner
membrane or lining of the bowels, and sometimes named, from the white
colour of their contents, _lacteals_ or _milk-bearers_ (from _lac_,
milk). These lacteals ultimately converge into one trunk, named the
_thoracic duct_ or _chest-pipe_ (from its course lying through the
_thorax_ or _chest_), and which terminates, as will be seen in a cut in
Chapter VI., in the great vein under the clavicle or collar-bone, hence
called _subclavian_ vein, just before the latter reaches the right side
of the heart; and there the chyle is poured into the general current of
venous blood.
But although thus mingled with the blood, the chyle is not yet
sufficiently capacitated for its duties in the system. To complete its
preparation, it still requires to be exposed to the action of the air
during respiration. This is accordingly done by its passing through
the lungs along with the dark and venous blood, which stands in need
of the same change. In the course of this process, both the chyle and
the venous blood are converted into red, arterial, or nutritive blood,
which is afterwards distributed by the heart through the arteries,
to supply nourishment and support to every part of the body. Hence
the change which takes place in the lungs is properly enough named
_sanguification_ or _blood-making_.[18]
The thickish yellow residue left in the _duodenum_ after the
separation of the chyle from the chyme, is that portion of the food
which affords no nourishment, and which, after traversing the whole
length of the intestinal canal, and undergoing still farther change,
is thrown out of the body in the shape of _fæces_ or excrement.
But in this course its bulk is increased, and its appearance changed,
by the addition of much waste matter, which, having already served its
purposes in the system, is at last, as will be afterwards shewn, thrown
out by the same channel.
* * * * *
With this general view of the nature of Digestion before us, we can now
examine more satisfactorily the structure and mode of action of each of
the organs concerned in effecting it. _Chymification_ being the
first step in the complicated process, we shall begin with the organ by
which it is performed, namely, the STOMACH.
In the lowest class of animals,--the Hydra, for example, which belongs
to the order of gelatinous polypi, and abounds in stagnant pools,--the
stomach is like a simple bag, devoid of any peculiar organization;
or, more properly speaking, the animal itself is nothing more than
a living stomach; for the minutest inspection can discover in it no
trace of any thing like vessels, nerves, brain, lungs, heart, or
other known organ. Even the experienced eye of Cuvier, aided by a
powerful microscope, could detect in their structure nothing more
than a transparent parenchyma, full of darkish grains or points, and
offering no trace of any distinguishable organs.[19] In form the animal
somewhat resembles the finger of a glove, the hollow in the centre
being appropriated for the reception of its food; and yet with all this
simplicity of structure, it not only moves and swims, but seizes its
prey by means of its tentacula, thrusts it into its cavity, and digests
it visibly--“_à vue d’œil_.” And what is still more strange, when
it is turned inside out, the surface which was formerly the exterior of
the body, now digests as actively and efficiently as if it had never
served any other purpose.
Bloodvessels being merely pipes serving for the conveyance of
nourishment from the place where it is stored up and prepared, to
those more distant parts which stand in need of it, it is obvious that
in animals of this very simple description, where every part of the
internal surface of the body is already in immediate contact with its
food, and itself imbibes or absorbs _directly_ all the nourishment
which it requires, they would be entirely superfluous, and accordingly
none are to be found.
Owing to this extreme simplicity of organization, a hydra may be
cut into pieces, each of which will become a perfect animal. But in
proportion as we ascend in the scale of creation, the organization
becomes more complicated, and the functions more numerous and also more
dependent on each other; so that, when we arrive at man--the highest
of all--we find that the loss or injury of any vital organ puts a stop
to, or impairs, the action of all the rest. It is impossible, however,
in an elementary work like this, to trace the gradation through the
different series of animals. We must confine our examination to man,
and only borrow from other creatures such illustrations as may be
necessary for throwing light upon the human structure.
In man, then, the stomach is a large membranous and muscular bag, lying
under the convexity of the lower ribs of the left side, and stretching
towards the right a little beyond the hollow commonly called the pit of
the stomach. In shape it somewhat resembles the bag of a bagpipe, as
will be seen from the figure on page 67; its left or larger extremity
being in contact with the ribs, and its right or narrow extremity
situated under the pit of the stomach.
The position of the stomach (St^m.) relatively to the chest, bowels,
and liver, will be understood by inspecting the figure on the next
page. It is separated from the cavity of the chest by the diaphragm or
midriff DD, with which its upper surface is in immediate contact, and
through which the gullet passes to enter its left extremity. Its right
or _pyloric_ extremity, marked P in the cut on the opposite page,
lies close to the lower surface of the liver (Liv^r.), the latter being
a little displaced to shew its situation. On the lower surface it has
the appearance of resting on the intestines, as if imbedded among their
folds.
[Illustration]
The parts of the stomach which have received names and require to be
noticed, are,--the _cardiac_ orifice (marked C in the next figure, and
so named from being near the κεαρ, _kear_, or heart), in which the
gullet terminates, and through which food and drink are introduced;
P, the _pylorus_, or pyloric orifice (from πυλωρος, _pyloros_, a
_gate-keeper_, because it allows none but digested food to pass out),
where the intestine called the _duodenum_ begins, and through which the
chyme passes after digestion is completed, and which, when the stomach
is full, is nearly on a level with the cardia, although when empty it
is lower; SS, the _smaller arch or curvature_; and GGG, the _greater
arch or curvature_. The spleen is attached to that part of the larger
arch marked with dotted points. From the situation of the cardia C, and
its connection with the gullet, it will be at once perceived that this
forms one of the points of attachment by which the stomach is retained
in its place.
[Illustration]
In size the stomach varies much in different individuals, as well as in
different animals, according to the bulk and quality of their food. As
a general rule, it is larger among the labouring poor than among the
rich, as the former require a larger quantity of their inferior food
to obtain from it an equal amount of nourishment. For the same reason,
animals which subsist on vegetable substances have a very capacious
stomach, while those subsisting on animal or concentrated food have it
simple and small. In man its capacity may be diminished or augmented
within certain limits, by corresponding modifications of diet. In
some gluttons, and in cases of diseased appetite, it has been found
of enormous dimensions; but this rule does not always hold, for the
stomach is sometimes smaller than usual in immoderate eaters, and then
its contents pass through only partially digested.
In accordance with this relation between the capacity and structure
of the organs of digestion and the quality of the food, the stomach
and intestines are found to be very small and short in carnivorous
quadrupeds and birds of prey, which are intended to live on
concentrated aliment. The same is the case with the granivorous or
_grain-eating_ birds, as their food also is contained in a small
bulk. But in herbivorous animals--in the food of which the nutritive
principle forms a very small proportion of the whole, perhaps not
one-twentieth, and which consequently require a large bulk of it for
their sustenance--the digestive apparatus is on a large scale, as any
one may conceive in a moment, by comparing the portly protuberance of
the cow with the lank paunch of the greyhound. The cow, in fact, is
little else but a living laboratory for the conversion of vegetable
into animal matter; and accordingly, not only is its stomach large
and complex, but its intestinal canal is nearly twenty-four times the
length of its body; whereas, in some carnivorous animals, the whole
intestine does not exceed once their own length.
[Illustration]
In ruminating animals, such as the sheep and ox, the stomach, as will
be seen from the annexed figure, not only is large, to adapt it to the
bulky nature of their food, but is complicated in its structure, to fit
it for effecting the great changes which vegetable aliment requires to
undergo before it can be converted into blood. It may indeed be said
to consist of four distinct stomachs conjoined. In the first of these,
AA, termed the _paunch_, the herbage is deposited when first
swallowed after hasty and ineffectual mastication. It there undergoes
a kind of maceration or steeping in a fluid provided for the purpose;
after which it passes from the paunch into a smaller bag, called the
_reticulum_, or bonnet, B, which, in some animals, such as the
camel and dromedary, is designed exclusively as a reservoir for water,
which being there stored up in large quantities, ready for use when
wanted, fits them in a wonderful manner for travelling through the
arid deserts where no water is to be obtained, and where, without some
such provision, they would of course soon perish. So admirably is the
reticulum adapted for this special purpose, that the water contained
in it undergoes little or no change either in quality or quantity,
although if it were collected in the ordinary digesting stomach, it
would be entirely absorbed in the course of a few minutes. It is not
even mixed with the food which is swallowed after it, as the animal has
the power of directing solids at once into the other cavities. From the
reticulum the alimentary mass is again returned to the mouth, there
to be thoroughly masticated and mixed with the saliva; after which it
descends a second time through the gullet: but instead of passing,
as before, into the paunch, it enters the third bag, _omasum_,
or many-plies, C, where it undergoes farther changes, and is then
transmitted to the fourth portion D, adjoining the pylorus, and named
_ab-omasum_, or red-bag. The last portion is exactly similar in
structure and in function to the simple stomach of man and the other
mammalia, and is in fact the true stomach, the other three being merely
preparatory organs.
The first part of the process, by which the food is taken hastily into
the paunch and afterwards sent back to the mouth in detached portions
for farther mastication, is called _rumination_ or _chewing
the cud_, and those species which perform it are thence called
_ruminating_ animals. Sheep and cows may be seen lying ruminating
in pasture-fields after having cropped as much herbage as fills the
paunch; and feeding is thus rendered to them a source of prolonged
enjoyment.
In those birds, again, which live on hard grain and seeds, and possess
no organs of mastication wherewith to bruise or grind them down,
another modification of the digestive apparatus is found. Nature
has furnished them with a membranous bag, called a _crop_ or
_craw_, into which the food is received, and where it is slightly
softened by a mucous fluid secreted from the surface of the bag. Thus
prepared, it is transmitted into an organ analogous to the stomach of
other animals, and called the _gizzard_, which has a very singular
structure. Its walls are composed of four distinct portions of thick
tough muscular substance, a large one at each side of the cavity, and
a small one at each end. The inner surface of the muscle is lined with
an extremely callous cuticle, approaching in hardness to cartilage or
horn. When the moistened grain is introduced into the gizzard from the
crop, the muscular walls of the gizzard enter into powerful action,
and, by their alternate contraction and relaxation, bruise the grains
as between two grindstones. In some birds their action is assisted by
a quantity of small gravel, purposely swallowed along with the food;
and it is well known to seamen that poultry never thrive on a voyage,
however well they may be fed, if gravel or coarse sand, as well as
food, be not placed within their reach. Mr Hunter has counted as many
as a thousand small stones in the gizzard of a common goose.[20]
The astonishing force with which the muscles of the gizzard act, and
the resistance of its lining membrane, may be conceived from the
experiments of Spallanzani and Reaumur, who compelled geese and other
birds to swallow needles, lancets, and other sharp metallic bodies,
and, on afterwards killing them, regularly found the points broken off
and the edges blunted, without any injury having been sustained by the
gizzard itself.
* * * * *
In STRUCTURE, the stomach of both man and animals consists
of three membranous layers or coats, of follicles or glands, and of
numerous bloodvessels and nerves.
The _first_ or _external_ layer is the smooth glistening
whitish membrane, which is familiar to all who have ever seen an
animal opened, or a fowl _drawn_ for cooking. It is a fold of
the tough shining membrane called _peritoneum_ (from περιτεινω,
_periteino_, I extend round), which lines the abdomen, and
constitutes the outer covering of all the abdominal organs. Its use
is obviously to strengthen the substance of the stomach, to assist in
binding down this and the other organs in their respective situations,
and, by the smoothness and constant moisture of their surfaces, to
enable them to move upon each other, and adapt themselves freely to
their different states of emptiness and distention.
* * * * *
The _second_, _middle_, or _muscular_ coat consists of fleshy fibres,
one layer of which, running longitudinally from the cardia to the
pylorus, seems to be a continuation of the longitudinal muscular fibres
of the gullet: another runs in a circular direction, embracing, as it
were, the stomach from one curvature to the other, and constituting
what are called the transverse fibres. A third and more internal layer
of this coat, is spoken of by Sir Charles Bell as a continuation of
the circular fibres of the gullet, which divide into two parcels, the
one distributed over the left or larger end, and the other over the
pyloric or narrower end.
The uses of the _muscular_ coat have, as we shall afterwards see, a
direct reference to the special function of digestion. By the joint
action of its longitudinal and circular fibres, the stomach is enabled
to contract, and shorten its diameter in every direction, so as to
adapt its capacity to the volume of its contents; while, by their
successive action, or alternate contraction and relaxation, a kind of
churning motion is produced, which contributes greatly to digestion by
the motion which it imparts to the food, and the consequent exposure
which it effects of every portion of it in its turn to the contact of
the gastric juice.
The force and rapidity of these muscular contractions are modified by
the more or less stimulant nature of the food, the state of health,
exercise, and other circumstances; but, according to Dr Beaumont, the
ordinary direction in which they take place, and the course which they
impart to the food, are as follows.
The alimentary _bolus_ or morsel, on entering the cardiac
orifice, turns to the left, follows the line of the great curvature of
the stomach towards the pylorus, returns in the line of the smaller
curvature, makes its appearance again at the cardia, and then descends
as before to the great curvature, to undergo similar revolutions till
digestion be completed. Each revolution occupies about from one to
three minutes, and its rapidity increases as chymification advances.
In treating of muscular action in the former volume, I pointed out
(p. 122) the necessity of the co-operation of a nervous stimulus to
produce the result; and remarked that there are two kinds of muscles,
one called the _voluntary_, which contract at _the command of
the will_, and the other the _involuntary_, over which the will
has no control, and which act only in obedience to their own peculiar
stimuli. Of the latter description are the muscular fibres of the
stomach. They contract when the stimulus of food is applied to them,
but we can neither contract nor relax them by an effort of the will,
nor are we even conscious of their existence.
It is, indeed, fortunate for us that the necessary motions of the
stomach are not entrusted to our guidance, like those of the hand or
foot. Supposing that we were to eat three meals a-day, the digestion of
each requiring three or four hours,--and that its management depended
entirely upon our superintendence,--our whole attention would be
required to the process, to the exclusion of every other duty, for ten
or twelve hours a-day; and every time that our thoughts wandered for a
few minutes, digestion would stand still, and the stomach be disordered
by the chemical decomposition of the food which would ensue, so that it
would be impossible for us to dedicate any time either to business or
to social enjoyment. But from all these inconveniences we are entirely
freed by the stomach being placed under the dominion of the involuntary
nerves, and so constituted as to perform its functions without any aid
from our will.
* * * * *
The _third_ and innermost coat, called the _mucous_ or _villous_, is
that smooth, unequal, velvety membrane, of a reddish-white or pale pink
colour, which lines the internal surface of the stomach. From being of
much greater extent than the other two coats, its surface is thrown
into _rugæ_, _plicæ_, _folds_, or _wrinkles_, which are simple in man,
but very marked in some animals, as seen familiarly in _tripe_. The
subjoined wood-cut, from the Library of Useful Knowledge, will give
some notion of their appearance. Near the pyloric orifice the villous
coat is doubled on itself, so as to form a ring, called the _valve_ of
the pylorus, the object of which is to prevent the too early exit of
the food; this object, however, it accomplishes, not by any contractile
power of its own, but by the aid of a layer of muscular fibres lying
behind it. The villous coat is constantly covered with a very thin
transparent viscid mucus, and its folds are always best seen in those
who die suddenly. After disease, when the stomach is relaxed, they
frequently disappear.
[Illustration]
In addition to the folds just described, the mucous coat contains a
great number of spheroidal glandular bodies or _follicles_, some
of them scarcely larger than pin-heads, which lie immediately beneath
and almost incorporated with it, and which are most numerous near the
pylorus. Physiologists are not entirely agreed whether the fluid
secreted by these follicles be the _gastric juice_ or merely the
mucus already referred to as lubricating the internal surface of the
stomach. The latter, however, is the opinion generally entertained,
and the one which is supported, as we shall afterwards see, by the
strongest evidence; the gastric juice being, in fact, secreted directly
from the capillary or _hair-sized_ vessels in which the minute
branches of the arteries terminate.
Of the _nerves_ and _bloodvessels_ supplying the stomach it
is unnecessary to say much. We shall afterwards have occasion to notice
the former at some length, and to the general reader the origin and
distribution of the bloodvessels are as unimportant as they would be
difficult of comprehension; for the nature of the red blood is the same
by whatever artery it is supplied, and that of the dark blood the same
by whatever vein it is returned to the heart. All that it is important
to know is, that the stomach receives a large supply of blood by means
of numerous bloodvessels, the principal of which, as represented on the
wood-cut at page 67, follow the course of GG the greater and SS the
smaller curvatures, and send off innumerable small branches as they
proceed to every part of the stomach. The _coronary_ artery and
the _pyloric_ branch of the _hepatic_ or liver artery go to
the smaller curvature, while another branch of the hepatic, and one
from the _splenic_ or spleen artery, are ramified on the larger
curvature.
In determining the uses of the internal or villous coat of the stomach,
we must begin by considering separately that of each of the elementary
structures of which it is composed--its follicles, bloodvessels, and
nerves--and the nature of the peculiar secretion, the gastric juice, to
which it gives rise.
The FOLLICLES pour out the bland viscid mucus which lubricates
the internal coat, and protects it in some degree from sustaining
injury by the immediate contact of irritating bodies. When the
follicles are diseased, as in what is called _water-brash_, they
sometimes throw out a large quantity of a ropy transparent fluid, which
oppresses the stomach and impairs digestion.
The BLOODVESSELS of the stomach, like those of every other
part, are more or less active according to the energy of its functions
at the time. In treating of the laws of exercise as applicable to all
living parts,[21] I took considerable pains to point out the relation
which the Creator has established between the activity of every organ
and the energy of its vital functions. When the brain is exercised and
the mind active, an augmented flow of blood takes place towards it
to support its increased action, of which the throbbing temples and
fiery complexion of a man in a paroxysm of rage are familiar examples.
When it is inactive, and the mind indolent, a diminished flow of blood
occurs. In like manner, when the muscles are called into vigorous
action, the circulation of the blood through them is quickened, and
their nerves are more than usually excited: greater waste of material
is caused by the increase of activity, and more blood, consequently,
is required to repair the waste and sustain their tone. This law was
so well known to the older writers, that it was announced by them
as an axiom in the very comprehensive phrase, _Ubi stimulus, ibi
affluxus_--“_Wherever a stimulus is, there is also an afflux._”
The stomach forms no exception to this general law of the animal
economy. When it is empty and idle, it is contracted upon itself into
comparatively small bulk; and its bloodvessels become shortened and
tortuous in a corresponding degree. The result is both a diminution of
their calibre and a slower circulation through their branches. But when
the stomach is full and active, the bloodvessels have free scope, their
tortuosity disappears, their diameter enlarges, and the circulation
through them becomes quicker, and fit for the rapid secretion of the
mucous and gastric fluids in the quantities which we have seen to be
required for the fulfilment of digestion. Accordingly, when the latter
process is going on, the small arterial branches ramified on the mucous
coat of the stomach become so multiplied and distended, as to impart
to it a deeper red colour than it has when the stomach is empty.
The increased afflux of red or arterial blood to the stomach during
digestion, is not merely inferred from the analogy of other organs.
Many opportunities have occurred of ascertaining the fact; and, as I
shall have occasion to mention, Dr Beaumont very often SAW it
take place.
A corresponding change occurs in the _veins_ of the stomach during
digestion. Their diameter becomes enlarged, their course more straight,
and the current of blood through them more rapid. As the minute or
capillary extremities of the arteries open upon the inner surface
of the stomach, and there _exhale_ a fluid secretion, so the
corresponding venous capillaries likewise open upon the same surface,
and _inhale_ or _absorb_ fluid, which they carry into the
general circulation. The rapidity with which this absorption sometimes
takes place is almost incredible; for a large draught of water may be
thus taken up in a few minutes. Fluids mixed with camphor or other
strong-scented substance have been given to animals as an experiment,
and, on killing them shortly afterwards, the peculiar smell has been
detected in the blood. Most liquids are thus not digested, but simply
absorbed.
Rapid, however, as the process is, poisons which enter the system by
absorption do not act by any means so instantaneously as those which
directly affect the nervous system.
* * * * *
In regard to the peculiar influence which each of the NERVES
ramified on the stomach exercises on its functions, much difference of
opinion still prevails. We may, however, gather some useful notions
by adverting to the different sources whence they are derived, and
comparing these with the purposes for which we know from analogy that
different kinds of nerves are required.
Strictly speaking, the nervous filaments supplied to the stomach
proceed from three distinct sources, and may be held to fulfil as many
distinct uses. In apparent accordance with this, we observe three, if
not four, distinct classes of operations going on in that organ, each
of which may, from analogy, be presumed to require a distinct nerve
for its performance. These are, first, the pleasurable consciousness
attendant on the presence of wholesome food in a healthy stomach, and
which becomes painful and disagreeable when the stomach is diseased
or the food of improper quality; secondly, the peristaltic or muscular
motion which commences the moment food is swallowed, and continues
till digestion is completed; and, lastly, the different processes of
circulation, nutrition, secretion, and absorption, which go on in the
component tissues of the stomach and support its life. To these ought
perhaps to be added the sensation in which the feeling of appetite
originates, and which we have already seen to be connected with the
pneumogastric nerve. But as it is still uncertain whether it and the
first of the three now named may not be modifications of the same
thing, I shall not insist on considering them as different.
Although we cannot state positively what particular nerve presides over
each of these functions, it may be mentioned that strong presumptive
evidence has been adduced, particularly by Brachet, to shew that
the _pneumogastric_[22] nerve is charged with the involuntary
motions of the stomach, as well as with the sense of its condition.
Food being the natural stimulus of that organ, as light is of the
eye, its presence alone, without and even against the will, suffices
to produce the contraction of its muscular coat; and accordingly, the
more stimulating the food, the more rapid and vigorous is the muscular
contraction which it excites. So far indeed do the stomachic nerves
respond to their own stimuli, that, if nauseous or other irritant
and indigestible substances be swallowed, the action of the muscular
coat becomes so violent as to excite sympathetically the simultaneous
contraction of the diaphragm and abdominal muscles, to aid in their
immediate expulsion by vomiting; and this is the reason why such
substances are in common use as emetics.
Magendie doubts whether these movements are in any measure dependent
upon nervous influence; but the fact of their being so seems to be
proved by the experiments of Gmelin and Tiedemann, who found them
constantly produced when the pneumogastric nerve was irritated either
by the scalpel or by the contact of alcohol. Brachet also, who examined
the subject with great care, obtained similar results; and the only
plausible argument against their conclusiveness consists in the double
function which seems thus to be assigned to a single nerve--that of
conveying to the brain a _sense_ of the state of the stomach,
and that of imparting _motion_ to its muscular fibres. Bracket,
however, turns this charge into an additional proof; for, on careful
dissection, it appears that the pneumogastric nerve is really a
compound of two distinct sets of fibres, intimately connected no doubt
in structure and in function, but each essentially distinct in its
origin, and so far fitted for a peculiar office.
When the pneumogastric or chief nerve of the stomach is tied or cut
through, and its ends separated so as to interrupt the flow of nervous
energy towards that organ, digestion is either entirely arrested or
greatly impaired. By the greater number of physiologists this result
is considered to arise from the consequent stoppage of that gentle
and continued agitation of the alimentary mass in the stomach which
is necessary for its thorough impregnation with the gastric juice,
and which we have seen to depend on a stimulus communicated to its
muscular coat by that nerve. By some, however, this explanation is
regarded as incorrect. Magendie and Dr Holland, for example, say that
they have sometimes observed digestion continue even after the division
of the nerve; and that, when it is retarded or impaired, the result
arises only from the troubled state of respiration which the cutting
of the nerve induces at the same time. To this, again, it is answered,
that Dupuytren has divided the nerve below the part where the pulmonary
branches are given off, and consequently left respiration unimpaired;
but that still digestion was arrested, provided a portion of it was cut
out so as not to allow the current of nervous influence to continue:
for if the two ends of the nerve be left nearly in contact, it appears
that little interruption of its action takes place.
Here, however, I cannot help observing, that, in drawing conclusions
from experiments of this nature, the constitutional disturbance
inseparable from the infliction of extensive wounds on living animals
is seldom taken sufficiently into account. As regards digestion, for
example, it is not to be expected that that function can be carried on
with all the regularity of health when the animal is suffering severe
pain, even although the stomach be left untouched. Brachet, indeed,
has shewn, by direct experiment, that digestion may be interrupted
almost as effectually by making an incision on the side or thigh
(provided it be sufficiently deep and painful to excite constitutional
disturbance), as by cutting the pneumogastric nerve itself. This being
the case, we must not be too hasty in considering every apparent
result as inseparably and exclusively connected with the individual
injury under our notice at the time; we must repeat our observations
under every variety of circumstances, and be careful to separate the
accidental from the essential, before admitting the inference to be
correct. It is, in fact, this unavoidable source of vagueness which so
often renders experiments on living animals as inconclusive as they are
inherently cruel.
But after making every allowance on this account, the experiments
on digestion have been so frequently repeated, and so extensively
varied, that the general results already noticed may safely be regarded
as demonstrated. On all hands, accordingly, the necessity of the
co-operation of the nervous energy in effecting it is admitted; for
no one seriously denies the fact, that retardation or total cessation
of digestion ensues, when the flow of the nervous fluid towards the
stomach is prevented by the division and separation of the cut ends of
the pneumogastric nerve, or by the operation of narcotics and the other
disturbing causes already alluded to. It is true that the _mode_
in which the nerve acts is not yet ascertained, although the fact
of its necessary co-operation is rarely disputed. As, however, the
direction of a current of galvanism to the cut end of the nerve next
the stomach suffices to re-establish digestion after that process has
been suspended by the interruption of the nervous influence consequent
on its division, we may reasonably infer that, in the healthy state,
the nerve merely transmits to the stomach a stimulus or energy
generated for the purpose either in the brain or in the spinal marrow
and ganglia--that the nerve, in short, acts only as a conductor, and
does not originate the influence which it evidently imparts. In
several of Brachet’s cases, indeed, as well as in those of Tiedemann,
the continued irritation of the cut end of the nerve proved sufficient
to carry on digestion to a certain point, by affording, in another way,
the necessary stimulus to the muscular contractions of the stomach: for
in all these experiments, digestion was found to have advanced almost
in exact proportion to the degree of admixture which had been effected
of the food with the gastric juice,--an admixture now ascertained to be
produced chiefly by the contractile power of the stomach itself.
* * * * *
The muscular contractions of the stomach being thus under the
guidance of the pneumogastric nerve, what are called its _vital_
functions--those by which its life is sustained--viz. circulation,
nutrition, secretion, and absorption, are generally considered to
be carried on under the influence of the great _sympathetic_
or _ganglionic_ nerve, so called from its very extensive
ramifications being supposed to bring the different parts of the system
into relation with each other, and which, accordingly, is found to
exist in animals that have neither brain nor spinal marrow, nor nerves
of voluntary motion. In man, however, the sympathetic nerve receives
filaments from the _sentient_ or _feeling_ part of the spinal
marrow, probably for the purpose of connecting more intimately the
organic with the higher functions of animal life. But as much obscurity
still prevails on this subject, and moreover we have no direct control
over the action of the ganglionic nerves, I shall not detain the reader
with any conjectural discussion, but rather request his attention
for a moment to the circumstance that it is through the medium of
the nervous communications above hinted at, that the very remarkable
influence which all must have experienced and observed as constantly
exerted by the mind and stomach on each other, is kept up--an influence
so powerful in its effects on both bodily and mental health, as to
require special notice when we shall treat of the practical application
of the present exposition.
The importance of the nervous agency in effecting digestion has been
denied, because we are not _conscious_ of the presence of food
in the stomach. But in health the want of such consciousness is a
privilege and not a defect; and it has been admirably pointed out by
Dr Southwood Smith,[23] that in possessing, as we do, the distinct
consciousness of a _pleasurable_ feeling in the stomach after
indulging in a suitable meal, we have all that is desirable for either
utility or enjoyment. If we were aware of the presence of every portion
of food which the stomach contains, and of the changes occurring in
each, our attention would be so disagreeably and unprofitably taken up
that we would pray to be delivered from the annoyance. Where, however,
from disease or the food being inappropriate, the stomach is injured
by what is eaten, consciousness then becomes painful for the express
purpose of warning us that mischief has been done, and that we must
take means for its removal. In some kinds of dyspepsia indeed, the
sensibility becomes exalted to an extraordinary degree. Barras who
suffered intensely from this cause, says of himself “the sensibility of
the stomach increased to a surprising extent; instead of organic it
became animal, to use the expression of Bichat. Every thing which took
place in the principal organ of digestion became as palpable to sense
as if it had taken place on the organ of touch, and the presence of
aliment was perceived as clearly as if it been under my hand.”[24]
The nerves of the stomach, it ought to be remarked, have a direct
relation to _undigested_ but _digestible_ substances; or
in other words, undigested food forms their natural and appropriate
stimulus. In consequence of this arrangement, when any body incapable
of digestion is introduced into its cavity, distinct uneasiness is
speedily excited, and an effort is soon made to expel it either
upwards by the mouth or downwards by the bowels. It is in this way
that bile in the stomach excites nausea, and that tartar emetic
produces vomiting. The nerves of the bowels, on the other hand, are
constituted with relation to the presence of _digested food_, and
consequently, when any thing escapes into them from the stomach in an
_undigested_ state, it becomes to them a source of irritative
excitement; and hence the colicky pains and bowel-complaints which
so commonly attend the passage through the intestinal canal of
such undigestible substances as fat, husks of fruits, berries, and
cherry-stones.
* * * * *
Such, then, are the component parts of the stomach, and such the uses
which they individually fulfil; but before we can consider them in
their combined form, there is still another agent, and an important
one in digestion, which has already been repeatedly named, and which,
though not a portion of the stomach, yet plays too conspicuous a part
in its operations not to require some separate notice--the GASTRIC
OR STOMACH JUICE.
The existence of a solvent fluid in the stomach has long been known,
and its uses suspected; but for our first accurate acquaintance
with its properties and mode of action, we are indebted chiefly to
the sagacity and persevering zeal of Spallanzani, who investigated
the subject with great care and success about the middle of last
century. Considering the peculiar difficulties by which the inquiry is
surrounded, it is offering no trifling homage to that distinguished
observer to say, that by means of numerous, varied, and well-devised
experiments on man and animals, he succeeded in overcoming most of the
obstacles which had baffled the ingenuity of his predecessors, and in
obtaining results, the general accuracy and importance of which are
now appreciated more and more highly, in proportion as our knowledge
advances and opportunities present themselves of bringing them to the
test of experience.
It is rarely, indeed, that we _can actually see_ what is going
on in a healthy stomach; but in a few instances this advantage has
been enjoyed, and turned to account in investigating the phenomena
of digestion. By far the most instructive example of this kind which
has ever occurred, came under the observation of Dr Beaumont of the
American army; and, as that gentleman eagerly embraced the opportunity
so unexpectedly afforded him, of testing the prevailing doctrines by a
series of experiments, continued during a period of several years, and
under various conditions of health and external circumstances, I shall
so frequently have occasion to refer to his observations, that it will
be useful to give a brief outline of the case before entering farther
upon the subject, in order that the reader may be enabled to judge for
himself what weight is due to Dr Beaumont’s evidence on any disputed
point.
Dr Beaumont, while stationed at Michillimackinac in the Michigan
territory in 1822, in the military service of the United States, was
called upon to take charge of ALEXIS ST MARTIN, a young Canadian of
eighteen years of age, good constitution, and robust health, who was
accidentally wounded by the discharge of a musket on 6th June 1822.
[Illustration]
“The charge,” says Dr Beaumont, “consisting of powder and duck-shot,
was received in the left side, at the distance of one yard from the
muzzel of the gun. The contents entered posteriorly, and in an oblique
direction, forward and inward; literally blowing off integuments and
muscles to the size of a man’s hand, fracturing and carrying away the
_anterior half of the sixth rib, fracturing the fifth, lacerating the
lower portion of the left lobe of the lungs, the diaphragm, and_
PERFORATING THE STOMACH.”
On the fifth day, sloughing took place; lacerated portions of the lung
and stomach separated, and left a perforation into the latter, “large
enough to admit the whole length of the middle finger into its cavity;
and also a passage into the chest half as large as his fist.” Violent
fever and farther sloughing ensued; and for seventeen days every thing
swallowed passed out through the wound, and the patient was kept alive
chiefly by nourishing injections. By-and-by the fever subsided, the
wound improved in appearance, and after the fourth week the appetite
became good, digestion regular, the evacuations natural, and the health
of the system complete. _The orifice, however, never closed_;
and at every dressing the contents of the stomach flowed out, and its
coats frequently became everted or protruded so far as to equal in
size a hen’s egg, but they were always easily returned. The prefixed
figure exhibits the appearance of the wound after it was healed. The
circumference of the wound EEEL, extended to about twelve inches; and
the opening into the stomach AAA, nearly in its centre, was about two
inches below the left nipple F. The folds of the villous coat are
visible at BC.
Some months after, St Martin suffered extremely from the death and
exfoliation of portions of the injured ribs and their cartilages, and
his life was often in jeopardy; but through the skill and unremitting
care with which he was treated by Dr Beaumont, he ultimately recovered,
and, in April 1823, was going about, doing light work and rapidly
regaining strength.
On 6th June 1823, a year from the date of the accident, the injured
parts were all sound, except the perforation into the stomach, which
was now two and a-half inches in circumference. For some months
thereafter the food could be retained only by constantly wearing a
compress and bandage; but early in winter, a small fold or doubling of
the villous coat began to appear, which gradually increased till it
filled the aperture and acted as _a valve_, so as completely to
prevent any efflux from within, but to admit of being easily pushed
back by the finger from without.
Here, then, was an admirable opportunity for experimenting on the
subject of digestion, and for observing the healthy and undisturbed
operations of nature free from the agony of vivisections, and from the
sources of fallacy inseparable from operating on animals. Dr Beaumont
was sensible of its value, and accordingly pursued his inquiries with
the most praiseworthy perseverance, and disinterestedness. Having been
fortunate enough to obtain a copy of his work, I shall not hesitate to
make free use of its contents.
Dr Beaumont began his experiments in May 1825, and continued them
for four or five months, St Martin being then in high health. In
the autumn, St Martin returned to Canada, married, had a family,
worked hard, engaged as a voyageur with the Hudson’s Bay Fur Company,
remained there four years, and was then engaged at a great expense
by Dr Beaumont to come and reside near him on the Mississippi, for
the purpose of enabling him to complete his investigations. He came
accordingly in August 1829, and remained till March 1831. He then went
a second time to Canada, but returned to Dr Beaumont in November 1832,
when the experiments were once more resumed, and continued till March
1833, at which time he finally left Dr Beaumont. He now enjoys perfect
health, but the orifice made by the wound remains in the same state as
in 1824.
Dr Beaumont describes the aperture in St Martin’s stomach as being
situated about three inches to the left of the cardia, near the left
or superior termination of the great curvature. When the stomach was
nearly empty, he was able to examine its cavity to the depth of five or
six inches by artificial distention. When it was entirely empty, the
stomach was always contracted on itself, and the valve generally forced
through the orifice, together with a portion of the mucous membrane
equal in bulk to a hen’s egg. After sleeping for a few hours on the
left side, the protruded portion became so much larger, as to spread
“over the neighbouring integuments five or six inches in circumference,
fairly exhibiting the natural _rugæ_, villous membrane, and mucous
coat, lining the gastric cavity. This appearance is almost invariably
exhibited in the morning before rising from bed.” Such was the very
favourable subject on whom Dr Beaumont’s observations and experiments
were made, and such were the numerous opportunities which he enjoyed
for repeating them, and verifying their accuracy. Having given this
outline, we now return to the consideration of the gastric juice, on
the origin and qualities of which it removes any uncertainty which
previously existed.
In treating of the properties of the gastric juice, I shall on all
disputed points give a decided preference to the observations of Dr
Beaumont over those of any other physiologist; because, although a few
cases have occurred, in which, from external wounds, direct access has
been given to the interior of the stomach, and Richerand and others
have availed themselves of the opportunities thus afforded of adding
to our knowledge of the digestive process, still, in most of them
which have been recorded, the patients were a comparatively short time
under observation, and were not sufficiently re-established in health
to admit of either extensive or conclusive experiments being made.
Whereas in the case which Dr Beaumont had the good fortune to meet
with, the patient remained under his eye for several years, and in the
enjoyment of the most robust health; so that ample time and opportunity
were afforded for every variety of experiments which reflection could
suggest, and for their subsequent repetition under such modifications
as seemed to be requisite for clearly distinguishing the accidental
from the constant and essential result. In addition to these reasons,
it ought to be added, in justice to the American physiologist,
that, from the excellent judgment with which he carried on his
investigations, and the scrupulous care with which he announces his
results and separates facts from theory, it is impossible not to place
great confidence both in his personal qualifications as an observer,
and in the general accuracy of his statements. Moreover, as he enjoyed
the rare advantage of _seeing_ what he describes to have taken
place in the stomach during healthy digestion, his evidence comes
before us with the strongest possible claims on our attention.[25]
The first disputed point which is conclusively settled by Dr Beaumont
is, that _the gastric juice does not continue to be secreted between
the intervals of digestion, and does not accumulate to be ready for
acting upon the next meal_. By inducing St Martin to fast for some
hours, and then placing him with the opening in the left side exposed
to a strong light, so as to give a distinct view of the cavity of the
stomach, Dr Beaumont found its only contents to consist of a little
viscid and occasionally slightly acidulated mucus mixed with saliva,
and in no instance did he perceive any accumulation of the proper
gastric juice. The same results had indeed been obtained by Tiedemann
and other physiologists before the publication of Dr Beaumont’s
memoir; but the evidence of the latter is so much more direct and
incontrovertible, that it may justly be regarded as setting the
question for ever at rest.
Having proceeded so far, Dr Beaumont next endeavoured to discover
at what time the gastric juice begins to be poured out, and under
what conditions its secretion is carried on; and here again ocular
inspection afforded him satisfactory results.
It has already been remarked, that, on pushing back the valve which
filled up the opening into the stomach, the cavity within became
visible to a considerable extent; and that when St Martin lay over for
a time on the left side, a portion of the villous coat, large enough
to exhibit several inches of its surface, generally protruded. Owing
to these circumstances, Dr Beaumont could easily observe what changes
occurred, both when food was swallowed in the usual way, and when
it was introduced at the opening left by the wound. Accordingly, on
examining the surface of the villous coat with a magnifying glass, he
perceived an immediate change of appearance ensue whenever any aliment
was brought into contact with it. The action of the neighbouring
bloodvessels was instantly increased, and their branches dilated so
as to admit the red blood much more freely than before. The colour
of the membrane consequently changed from a pale pink to a deeper
red, the vermicular or _worm-like_ motions of the stomach became
excited, and innumerable minute lucid points and very fine nervous
and vascular papillæ could be seen arising from the villous coat,
from which distilled a pure, colourless, and slightly viscid fluid,
which collected in drops on the very point of the papillæ and trickled
down the sides of the stomach till it mingled with the food. This
afterwards proved to be the secretion peculiar to that organ, or, in
other words, the true _gastric juice_; the mucous fluid secreted
by the follicles, which some have mistaken for it, is not only more
viscid, but wants altogether the acid character by which it is
generally distinguished.
Pursuing his experiments, Dr Beaumont then found that the contact not
only of food but of any mechanical irritant, such as the bulb of a
thermometer, or other indigestible body, invariably gave rise to the
exudation of the gastric fluid from these vascular papillæ; but that,
in the latter cases, the secretion always ceased in a short time, as
soon apparently as the organ could ascertain that the foreign body was
one over which the gastric juice had no power. But the small quantity
obtainable in this way is perhaps more pure and free from admixture,
and therefore better adapted for examination, than any which can be
procured under any other circumstances.
Various methods have been employed for procuring the gastric fluid in
a state of purity. Pieces of dry sponge, inclosed in a small hollow
perforated ball with a string attached to it, have been swallowed both
by man and by inferior animals, and afterwards withdrawn to have the
juice expressed from them. In some instances the stomachs of criminals
and animals killed after fasting have been opened, and the secretion
collected. At other times the juice has been procured by voluntary or
artificial vomiting. None of these methods is equal to that employed
by Dr Beaumont; but of the three the first is unquestionably the best,
because, although no gastric juice previously exists, the very contact
of the ball excites the secretion of a quantity sufficient to moisten
the sponge. In the second mode of proceeding, any portion of juice
secreted in consequence of a stimulus applied _after_ the stomach
is opened, must necessarily be very small and rendered impure by the
large admixture of mucus which it will contain; while, by the third
method, as the gastric juice does not exist ready made in the stomach,
either none but merely mucus will be procured, or it will be expelled
mixed with the food or substance which had previously elicited its
secretion.
Gastric juice, in its purest form, and unmixed with any thing except
the small portion of mucus from which it can never be obtained
entirely free, is described by Dr Beaumont to be a clear transparent
fluid, without smell, slightly saltish (probably from the admixture
of mucus), and very perceptibly acid. Its taste, he says, resembles
that of thin mucilaginous water, slightly acidulated with muriatic
acid. It is readily diffusible in water, wine, or spirits, and
effervesces slightly with alkalis--a direct proof of its acid nature.
It coagulates albumen, and is powerfully antiseptic, checking the
progress of putrefaction in meat. When pure it will keep for many
months, but when diluted with saliva it becomes fetid in a few days.
According to Professor Dunglison, to whom some was submitted by Dr
Beaumont for analysis, it contains free _muriatic_ and _acetic_
acids,--_phosphates_ and _muriates_ with bases of _potassa_, _soda_,
_magnesia_, and _lime_,--together with an animal matter soluble in
cold but insoluble in hot water. Tiedemann and Gmelin, again, describe
it as composed principally of _muriatic_ and _acetic_ acids, mucus,
saliva, _osmazome_, _muriate_, and _sulphate of soda_, with little or
no albumen; and, according to the same physiologists, the proportion
of acid is always greatest when vegetables or other substances of
difficult digestion constitute the chief part of the diet. Other
chemists give an analysis somewhat different from either of these; a
circumstance which was, indeed, to be expected, considering not only
the differences caused by variations of diet and of health, but also
the necessarily different degrees of purity of the fluid submitted to
examination.
The most remarkable property of the gastric juice is unquestionably
the power which it possesses of dissolving and reducing to the
appearance of a soft thickish fluid mass every thing in the shape of
food which is submitted to its action,--while it exerts no perceptible
influence on living or inorganic matter; for, so far as is yet known,
nothing which is not organized, or which is still alive, can serve
as nutriment for the animal frame. Water is the only inorganic body
which is taken into the system for its own sake, and all mineral and
other inorganic productions enter it as component parts of previously
organized substances of either an animal or a vegetable nature. To
a great extent, indeed, vegetation seems to be merely a process for
the conversion of inorganic matter into a proper nutriment for the
support of animal life; and many species of animals seem in their
turn to be little else than living machines for the conversion of
vegetable substances into a nutriment fit for other species by which
they are intended to be devoured. It is true that, in some parts of
South America, the natives, pressed by want, consume quantities of a
soft unctuous clay, which is of course destitute of organization; but
as there is every reason to believe that no nourishment is derived
from it, and that it merely serves to allay the pangs of hunger, such
instances form no exception to the general rule.
It would have been easy for the Creator to bestow such a structure on
all animals, as to make them subsist entirely on vegetable aliment. But
the arrangement which He has seen fit to adopt, is the source of an
infinitely greater amount of active enjoyment than what could otherwise
have existed. Had there been no beasts of prey, the world would soon
have been overrun with herbivorous creatures to such an extent, that
their numbers would speedily have become excessive in reference to the
possible supply of food, and there would have been infinitely more
suffering from starvation and disease, than what actually arises out
of their existing relation to each other. On the present plan, there
is ample food and enjoyment for all; and when the time does arrive
when one animal must become the prey of another, the deprivation of
life is in most cases unforeseen, and the suffering which attends it
is in general only momentary in duration. There is thus both complete
enjoyment of life while it lasts, and a great additional field opened
for the support of an immense class of animals, which, with their
present constitution, could not otherwise have existed at all.[26]
The gastric juice, as already remarked, has no power over living
animal matter,--a most wise and admirable provision, since otherwise it
would at once have attacked and destroyed the very organ which produces
it. This is the reason why certain worms are able to exist in the
stomach of man and other animals; and if it were possible for an oyster
swallowed directly from the shell to continue to live, it would also
effectually resist every attempt at digestion. But it, in common with
most other beings, soon perishes in circumstances so foreign to its
habits; and when once dead, the gastric juice assumes the mastery, and
speedily converts it into chyme.
If any thing could have opened Montègre’s eyes to the fallacy under
which he laboured in considering the gastric juice as almost identical
with saliva, the circumstance we are now to mention would have
sufficed. When a person, previously in good health, dies by a violent
death, or when an animal is killed soon after a meal, it very often
happens that, on opening the body after an interval of some hours,
the stomach is found to be eroded, and its contents poured into the
cavity of the abdomen, precisely as if a hole had been formed in it by
ulceration. It was long before the reason of this was discovered; but
at length it was ascertained to arise from _the action of gastric
juice (the abundant secretion of which was provoked by the immediately
preceding meal) upon the substance of the stomach, now subjected to
its power from being deprived of life_. This fact has been so often
verified, that it is by all admitted as incontrovertibly true.[27] If,
therefore, the gastric juice be merely saliva and mucus, we might
expect to find after death distinct traces of similar results from the
contact of saliva within the mouth or gullet; but _there_ no such
erosion is ever witnessed, nor, as Montègre himself admits, does saliva
exert any solvent power whatever over dead animal matter out of the
body. These facts appear quite sufficient to convince any unprejudiced
mind.
The power of _coagulating_ milk, and albumen or the white of
eggs, is another remarkable property of the gastric juice,--and one so
familiarly known, that in dairies an infusion of the stomach of the
calf is in common use, under the name of runnet or rennet, for curdling
milk. In infants, also, we know that the nurse’s milk has scarcely
reached the stomach before coagulation takes place; a fact which leads
many experienced mothers to infer that the infant is already suffering
from acidity, and to counteract the supposed evils by repeated doses
of magnesia--which, of course, do more harm than good. The coagulation
of milk in the stomach, is so far from being a morbid process, that
milk cannot be properly digested without it. By the separation
and absorption of the fluid whey, the curd is reduced to a proper
consistence for being acted upon, both by the gastric juice itself and
by the contractions of the muscular coat.
The gastric juice is also powerfully _antiseptic_; that is to say,
it prevents animal substances from becoming putrid, and even renders
sweet such as have advanced a considerable way towards putrefaction.
Dr Beaumont mentions that the pure juice will keep unchanged for almost
any length of time, and according to Spallanzani meat may be preserved
in it without taint for five or six weeks, or even longer. This
antiseptic tendency of the gastric fluid, accounts for the circumstance
that little or no mischief results from the common practice among
epicures, of not making use of game till the putrefactive process is
advanced farther than is agreeable to the palates of the uninitiated.
The qualities of the gastric juice are so directly adapted to the
natural food of the animal, that flesh introduced into the stomach of
an ox or a sheep, for example, undergoes scarcely any change; while
vegetable food, on the other hand, remains equally undigested in that
of a beast of prey. Thus, “when a hawk or an owl has swallowed a small
bird, in the stomach of which have been seeds, these bodies are not
dissolved by the gastric fluid,”[28] but pass through the intestines
unaltered. Man, the dog, and some other creatures, possess the power of
digesting all sorts of aliment, whether vegetable or animal, and are
hence called omnivorous or all-eating; but even in them, the relation
which the properties of the gastric juice bear to the qualities of
the food chiefly or exclusively used is so close, that, when a widely
different kind is suddenly resorted to, indigestion is the almost
inevitable consequence,--because then the gastric juice has not had
time to acquire its requisite adaptation to the new materials on which
it has to act. Hence also the danger arising from suddenly eating a
full meal after having been long famished. The stomach accustomed for
a time to the smallest quantity, is no longer able to provide gastric
juice sufficient for the purposes of digestion; and being irritated
by continued craving, its secretions are vitiated and its sensibility
exalted to such a degree as to require the wisest management to enable
it to regain its healthy tone.
The gastric juice of carnivorous animals differs even in its chemical
constitution from that of the herbivorous; a circumstance which
accounts for the difference observed in their action. In the former,
such as that of birds of prey, serpents, and fishes, no free or
uncombined acid can be detected, although it is invariably found in
the gastric fluid of vegetable-eaters. In crows and dogs, on the other
hand, and such animals as can live on either kind of aliment, it is
never acid except when they have been fed _chiefly_ on grain or
plants. In man, the same relation has, by numerous experiments, been
ascertained to exist.
But although, in every class of living beings, the gastric juice is
constituted with a direct relation to its natural food, still its
qualities may be so much modified by a very gradual change of diet, as
to fit it for digesting aliment of a very dissimilar or opposite kind.
Thus, in the natural state, the stomach of a sheep exerts scarcely
any action on beef or mutton; but if the change from the one kind of
food to the other be made by slow degrees, the gastric juice will in
the end become so essentially altered, as to enable it to digest both.
In this way, as is mentioned by Delabere Blaine,[29] a horse at the
Veterinary College was supported for some time by animal matter alone;
while others have subsisted on dried fish, or on milk. It has been
shewn, also, by John Hunter, Spallanzani, and others, that eagles,
falcons, owls, pigeons, and domestic fowls, may for a time be fed on
aliments altogether foreign to their natural habits. But these facts
only chew the extent to which Nature will go, on an emergency, for the
preservation of life; and no more indicate the equal fitness of both
kinds of aliment, than the fact of some men being able to stand for
a few minutes on their heads proves an inverted position to be the
natural attitude of the human race.
In consequence of this adaptation of the gastric juice to the nature
of the food, it is obvious that _sudden and extreme changes from one
kind of diet to another must be injurious_, because the stomach
has not time to modify its secretions sufficiently to meet the
altered demand made upon its powers. This, accordingly, is one of the
reasons why so much caution is used in bringing horses into condition
after having been for some time in the pasture-field. When they have
previously been on dry food in the straw-yard, corn may be given with
greater safety: so that it is the change, not so much in quantity as in
_kind_ of aliment, which causes the risk. And, on this account,
when a horse is to be put upon hard food, after having been fed on
grass or other succulent vegetables, Blaine recommends, not only that
hay and corn should be given in very small quantity at first, but
that the hay should be moistened, and the corn _mixed with bran and
mashed_; by which means having acquired a greater analogy to grass,
it will be more easily acted upon by the gastric juice, which has been
previously adapted for green food.
Even in man, the gastric juice undergoes considerable modifications,
not merely according to the kind of aliment habitually used, but also
according to the time of life, the wants of the system, the season of
the year, and the state of the health; so that while sudden and great
changes from one kind of diet to another are positively hurtful on the
one hand, absolute uniformity is not less objectionable on the other,
because it leads to so great a uniformity in the quality of the gastric
juice habitually secreted as to render it incapable of acting with
due effect on any accidental variety of food, to which a change of
circumstances may compel us.
Many attempts have been made to ascertain to which of the elements of
the gastric juice its power is chiefly to be ascribed, and experiments
have been instituted on them individually to discover which of them
is most nearly analogous to it in effect. From the general results,
it appears that acetic acid (vinegar) and muriatic acid have a wider
range of influence, and produce solvent effects more closely resembling
those of gastric juice, than any other known substances. Both of these
acids, it will be recollected, are constituent elements of the gastric
fluid; and it has, in consequence, been argued, that to them it is
indebted for all its energy. And, indeed, without laying too much
stress on this real or supposed analogy, it is impossible to overlook
the well-known fact, that scurvy, and a highly alkaline state of the
system, are generally induced by a diet restricted for a long time to
animal food alone, and are prevented or cured most easily by a free use
of lemon juice or of vegetable matter, either fresh or fermented. In
these circumstances, the vegetable acid is probably efficacious both by
directly improving digestion, and by combining with the excess of the
alkaline salts already existing in the system. It is worthy of remark,
too, that in weak stomachs _acidity_ is almost invariably induced
by the use of vegetable food, possibly to some extent for the very
purpose of effecting its digestion; for it has been ascertained beyond
a doubt, that in herbivorous animals the gastric juice always contains
some free or uncombined acid--and in man also, after living much on
vegetables for some time.
The necessity of acid for the chymification of vegetable food, affords
an explanation of the fondness which the Germans and Dutch display for
_saur-kraut_--or cabbage in a state of acetous fermentation--and
of its alleged easy digestibility. It explains, also, the general use
of vinegar along with salads, cucumbers, oysters, salmon, and other
substances of difficult digestion, and shews that its utility is not
imaginary, but loudly proclaimed by Nature’s own acts.
Another important principle, which Dr Beaumont conceives to be
established by his numerous experiments, and which forced itself upon
him by degrees, is, that in health THE GASTRIC SECRETION ALWAYS
BEARS A DIRECT RELATION TO THE QUANTITY OF ALIMENT NATURALLY REQUIRED
BY THE SYSTEM; so that, if more than this be taken, there will
necessarily be too small a supply of the juice for the digestion of
the whole. The principle here laid down is in perfect harmony with the
sympathy which we have seen to exist between the stomach and the rest
of the body, and therefore not only is highly probable in itself, but,
if sound, will prove a most valuable guide in the practical regulation
of diet. The number of phenomena which it explains, and its general
applicability to daily use, afford no small presumption of its truth.
When, for example, we eat more than the wants of the system require,
indigestion will follow, because there will be more food in the stomach
than what the quantity of gastric juice provided is able to dissolve;
the proportion of the juice secreted being in relation, not to what we
eat, but to the actual wants of the system, which, in the case supposed
we have greatly exceeded. Here a remarkable harmony will be perceived
between the quantity of the secretion and the true indications and uses
of appetite as a guide to diet, explained in a preceding chapter (p.
21).
The gastric secretion, and the appearance of the villous coat, undergo
great modifications during disease, and on this subject also Dr
Beaumont’s observations are highly valuable; because, instead of merely
inferring, as others are obliged to do, he enjoyed the privilege of
SEEING with his eyes what was actually going on. In the course
of his attendance on St Martin, he found that, whenever a feverish
state was induced, whether from obstructed perspiration, from undue
excitement by stimulating liquors, from overloading the stomach, or
from fear, anger, or other mental emotion depressing or disturbing
the nervous system, _the villous coat became sometimes red and dry,
and at other times pale and moist, and lost altogether its smooth
and healthy appearance_. As a necessary consequence, the usual
secretions became vitiated, impaired, or entirely suppressed; and the
follicles from which, in health, the mucus which protects the tender
surface of the villous coat is poured out, became flat and flaccid, and
no longer yielded their usual bland secretion. The nervous and vascular
papillæ, thus deprived of their defensive shield, were then subjected
to undue irritation. When these diseased appearances were considerable,
the system sympathized, and dryness of the mouth, thirst, quickened
pulse, and other symptoms, shewed themselves; and NO GASTRIC JUICE
COULD BE PROCURED OR EXTRACTED EVEN ON THE APPLICATION OF THE USUAL
STIMULUS OF FOOD.
These facts, if correctly observed, are of extreme importance; and
from the care with which Dr Beaumont pursued his investigations, and
their accordance with the facts recorded by preceding physiologists,
I do not think their general accuracy can be called in question. The
dry irritated appearance of the villous coat, and the absence of the
healthy gastric secretion in the febrile state, not only explain at
once the want of appetite, nausea, and uneasiness generally felt in
the region of the stomach, but shew the folly of attempting to sustain
strength, by forcing the patient to eat when food cannot be digested,
and when Nature instinctively refuses to receive it.
* * * * *
Before dismissing this part of the subject, it may be remarked, that
the alleged sympathy of the stomach with the wants of the body has
been denied, because the sense of hunger disappears the moment food
is swallowed, or the stomach is distended even with clay or saw-dust,
although the actual wants of the system cannot by possibility have
been supplied in either case. But these facts seem to me rather to
justify the inference that a sympathy does exist. Hunger ceases when
_food_ is taken, simply because _now_ the condition of the
stomach is in the desired relation to the state of the body, and
the nerves consequently feel and transmit this impression to the
more distant parts. In the other case, again, it ceases because the
stomach cannot at first distinguish what is food from what is not;
and, therefore, when distended, expresses content, because it feels
satisfied that it has been honestly dealt with, and got what it
wanted. But whenever it discovers the cheat, which it does in no long
time, hunger returns, and can be properly appeased only by digestible
substances. Dr Beaumont indeed expressly mentions, that, although the
gastric secretion _commences_ the moment any indigestible body
touches the mucous surface of the stomach, it invariably _ceases_
soon after discovering that the substance is one over which it has no
power,--thus strongly confirming the existence of the sympathy. Here
it may be also proper to observe, that from the frequent and pointed
references which I have made to the results obtained by Dr Beaumont,
some of my readers have imagined that I claimed for him the merit
of the original discovery of all the truths which his experiments
tend to establish. Nothing, however, was farther from my intention,
and accordingly on page 87 I speak distinctly of his having eagerly
embraced the opportunity afforded him of “_testing the prevailing
doctrines_” on digestion; and on page 93 and other places I state
that the same results had _previously_ been arrived at by
Tiedemann and other observers, but that the evidence in their favour
adduced by Dr Beaumont was “more direct and incontrovertible,” and
therefore more conclusive than their’s,--a position wholly at variance
with any claim of _discovery_ on his part. Indeed, the utter
absence of pretension in Dr Beaumont’s work is one of its most pleasing
characteristics.
CHAPTER V.
THEORY AND LAWS OF DIGESTION.
Different theories of
Digestion--Concoction--Fermentation--Putrefaction--Trituration--Chemical
solution--Conditions or laws of digestion--Influence of gastric
juice--Experiments illustrative of its solvent power--Its
mode of action on different kinds of aliment--beef, milk,
eggs, soups, &c.--Influence of temperature--Heat of about
100° essential to digestion--Gentle and continued agitation
necessary--Action of stomach in admitting food--Uses of its
muscular motion--Gastric juice acts not only on the surface of
the mass, but on every particle which it touches--Digestibility
of different kinds of food--Table of results--Animal food
most digestible--Farinaceous next--Vegetables and soups
least digestible--Organs of digestion simple in proportion
to concentration of nutriment--Digestibility depends on
adaptation of food to gastric juice more than an analogy of
composition--Illustrations--No increase of temperature during
digestion--Dr Beaumont’s summary of inferences.
Before entering upon the consideration of the theory of digestion which
naturally evolves itself from the facts expounded in the preceding
chapter, it may be of advantage to turn for a moment to the various
theories which have prevailed since the subject first attracted the
attention of the learned.
Hippocrates regarded digestion as a kind of _concoction_ or
_stewing_; and many of his followers believed that it is effected
in the stomach by the agency of heat alone, much in the same way as
food is cooked over a fire. It is quite ascertained that heat favours
the process, but it is pure absurdity to maintain that that agent alone
will accomplish digestion.
Others of the older physiologists contended, that chymification results
from simple _fermentation_ of the alimentary mass, and referred
to the gas disengaged during difficult digestion, as a proof that the
process of fermentation goes on. But it is now demonstrated, that
the tendency of healthy digestion is rather to arrest than to induce
fermentation, and that the latter takes place only when disease exists,
or when more food has been swallowed than the quantity of gastric juice
secreted by the stomach is able to dissolve. Moreover, the products of
digestion and of fermentation are so extremely different, that it is
impossible to believe them to originate from the same chemical action.
The next theory which prevailed considered digestion to be the result
of the _putrefactive_ process. The single fact that the gastric
juice not only arrests putrefaction, but even restores to sweetness
meat in which that process is begun, is sufficient to demonstrate the
wildness of such a supposition.
Another set of physiologists imagined that _trituration_ would
account best for all the changes occurring in the food during
digestion; and consequently regarded the chyme as a sort of emulsion
formed by the intimate mixture of the aliment with the juices of the
stomach, just as an emulsion is formed by rubbing down almonds in a
mortar. The advocates of this theory referred for proofs not only to
the contractile motions of the stomach, already noticed, but to the
muscular apparatus for trituration which forms so remarkable a feature
in the gizzard of granivorous birds. But, in adopting this conclusion,
they forgot that in birds the triturating apparatus does not digest,
but serves, like the organs of mastication in man and quadrupeds,
merely to bruise the grain on which the animal lives. In birds, in
fact, digestion _begins_ only _after_ the trituration is
finished.
A more recent and much more accurate view of digestion, is that which
considers it as neither more nor less than a _chemical solution_
of the food in the gastric juice. This theory is supported by a
greater number of facts and experiments than any other; but although
substantially correct, it is perhaps too exclusive and limited in its
principles. It is true that, by the agency of gastric juice on food out
of the body, a change very similar to chymification can be effected
on it; but when we remember that _chyme_ or the _result_ of
real digestion, is essentially the same in its elementary or component
principles, whatever be the kind of food from which it is formed,--and
that, as yet, we are acquainted with no purely chemical agent, which,
applied to different substances, gives rise to the same uniform
product,--we shall be more willing to believe that chymification is
neither a purely mechanical nor a purely chemical operation; but the
result of a vital process, to which both mechanical and chemical forces
contribute, and which no action or combination of inanimate matter can
either exactly imitate or supersede.
To enable ourselves to appreciate correctly the nature of digestion, we
must begin by considering the conditions essential for its performance,
or without which it cannot be carried on.
The FIRST indispensable requisite is an _adequate supply of gastric
juice_, and its _thorough admixture with every particle of the food_
on which it is to operate. The SECOND is _a steady temperature of
about 98° or 100° Fahr._; and the THIRD is _the gentle and continued
agitation of the alimentary mass in the stomach while digestion is
going on_.
In illustration of the influence of the FIRST condition. I
may refer to the experiments already mentioned as having been made
by Spallanzani, Stevens, and others, to shew the solvent power of
the gastric juice on food even out of the body. Spallanzani states,
that when small portions of well-masticated beef or mutton are placed
in a vial with a due proportion of gastric juice, and the requisite
temperature and gentle agitation are secured by placing the vial in
the arm-pit, the appearances presented at the end of a few hours
are extremely analogous to those observed in the natural process of
chymification; the meat being in both cases converted into the soft
greyish mass of a pultaceous consistence called chyme.
Dr Beaumont, who was well aware of the importance of Spallanzani’s
researches, and of the almost universal adoption of his views by
succeeding physiologists till confidence in their accuracy was for a
time shaken by the bold and fallacious assertions of Montégre, felt
that the opportunity afforded him by St Martin’s wound for verifying or
disproving the experiments on which these views were founded, was much
too valuable to be lost. He therefore entered upon a long series of
investigations, of which the following is an imperfect, though I hope
instructive, abstract.
To test the reality of the solvent powers ascribed to the gastric
juice, Dr Beaumont withdrew from St Martin’s stomach about one ounce
of it, obtained after a seventeen hours’ fast, by introducing first a
thermometer to induce the secretion, and then a gum-elastic tube to
carry it off. Into this quantity, placed in a vial, he introduced a
piece of _boiled recently-salted beef_, weighing three drachms.
He then corked the vial tightly, and immersed it in water raised to
the temperature of 100°, which he had previously ascertained to be
the heat of the stomach when the secretion was going on. In _forty
minutes_, digestion had distinctly commenced on the surface of
the beef. In _fifty minutes_, the fluid became quite opaque and
cloudy, and the texture of the beef began to loosen and separate. In
_sixty minutes_, chyme began to be formed. In _one hour and a
half_, the muscular fibres hung loose and unconnected, and floated
about in shreds. In _three hours_, they had diminished about
one-half. In _five hours_, only a few remained undissolved. In
_seven hours_, the muscular texture was no longer apparent; and in
_nine hours_ the solution was completed.
To compare the progress of digestion in the natural way with these
results, Dr Beaumont, at the time of commencing the experiment just
described, suspended a piece of the same beef, of equal weight and
size, within the stomach by means of a string. At the end of the
_first half hour_ it presented the same appearances as the piece
in the vial; but when Dr Beaumont drew out the string at the end of
_an hour and a half_, the beef had been completely digested
and disappeared, making a difference of result in point of time of
nearly seven hours. In both, the solution began on the surface, and
agitation accelerated its progress by removing the external coating of
chyme as fast as it was formed. When the experiment was repeated with
chicken instead of beef, the solution was slower, from the greater
compactness of the chicken not allowing the gastric fluid to penetrate
its substance so readily. Had the beef and chicken been masticated
before being subjected to experiment, the difference between them in
the rapidity of digestion would probably have been less.
To ascertain still more accurately the difference between _natural_
and _artificial_ digestion (the one _in_ and the other _out_ of
the stomach), Dr Beaumont put twelve drachms of _recently-salted
boiled beef_ into a vial, with the same number of drachms of fresh
gastric juice obtained through the opening of the stomach after a
fast of eighteen hours; and then placed the vial in a basin of water
on a sand-bath, where he kept it at the heat of 100° Fahr., and
continued to agitate it gently. Digestion soon commenced and went on
uniformly for about six hours, when it ceased. One-half of the meat
was then dissolved, and the texture of the remainder loosened and
tender,--resembling the same kind of aliment when ejected from the
stomach partly digested some hours after a meal, as frequently seen
in cases of indigestion. On weighing the undissolved portion which
remained after all action had ceased, six drachms and twelve grains of
the beef were found to have been digested by twelve drachms, or nearly
double its weight, of gastric juice. It thus appears that a given
quantity of gastric fluid can digest only a relative proportion of
meat; so that, when more is eaten than what there is juice sufficient
to dissolve, stomachic disorder must necessarily follow. In this latter
case, Dr Beaumont found that _the addition of fresh juice causes
digestion to be resumed_.
To discover what influence would be exerted on food masticated,
swallowed, and mixed with the gastric juice in the usual way, and then
withdrawn from the stomach, Dr Beaumont gave St Martin an ordinary
dinner of _boiled salted beef, bread, potatoes, and turnips_, with
a gill of pure water for drink; and twenty minutes afterwards drew
off through the opening about a gill of the contents of the stomach
into an open mouthed vial. In this short space of time digestion had
already commenced, thus negativing the common notion that an hour
elapses before it begins. The vial was now placed in a water-bath, at
a temperature of 100°, and continued there for five hours. Examined at
the end of that time, the whole contents were found to be dissolved.
On then extracting an equal quantity of chyme from the stomach, and
comparing it with the solution in the vial, little difference was
observable between them, except that the process had been somewhat more
rapid in than out of the stomach. But this experiment is remarkable
in another point of view, as shewing that _in the short space of
twenty minutes enough of gastric juice had been secreted for the entire
completion of digestion_.
With a view to verify these results, and also to discover the
comparative digestibility of different kinds of aliment, Dr Beaumont
gave St Martin for dinner eight ounces of _recently-salted lean
beef_, four ounces of _potatoes_, some _bread_, and four
ounces of boiled _turnips_. After fifteen minutes he withdrew a
portion of the contents of the stomach, and found that some of the meat
had already been slightly digested. In a second portion, withdrawn at
the end of forty-five minutes, fragments of the beef and bread were
perceptible, and in a still more advanced state of digestion; the
meat was in small shreds, soft and pulpy, and the fluid containing it
had become more opaque and gruel-like in appearance. When two hours
had elapsed, a third quantity was taken out, at which time nearly all
the meat had become chymified and changed into a reddish-brown fluid;
but _small pieces of vegetable matter now presented themselves for
the first time, but in a state of digestion so much less advanced_
than the meat, that their peculiar structure was still distinctly
visible. Some of the second and third portions, put into a vial and
treated in the usual way, advanced to complete digestion, as in the
other experiment, except that the process was slower, and that a few
vegetable fibres remained to the last undissolved; thus confirming the
general opinion that vegetables are more difficult of digestion than
animal substances.
The _mode_ of solution by the gastric juice varies according to
the nature of the food on which it acts. We have seen that it gradually
reduces solids to a soft and fluid state; but its effect on milk and
albumen is different. It begins by _coagulating_ them so as to
give them the requisite consistence for being affected by the muscular
contractions of the stomach, and impregnated with the juice. Fifteen
minutes after St Martin had drunk half a pint of milk, a portion
taken out of the stomach by Dr Beaumont presented the appearance of
a fine loosely-coagulated substance, mixed with a semi-transparent
whey-coloured fluid. A drachm of warm gastric juice poured into two
drachms of milk, at a temperature of 100°, produced a precisely similar
appearance in twenty minutes. In another experiment, when four ounces
of bread were given along with a pint of milk, and the contents were
examined at the end of thirty minutes, the milk was coagulated, and the
bread reduced to a soft pulp floating in a large proportion of fluid.
In two hours the whole was digested.
When the _white_ or _albumen_ of two eggs was swallowed on
an empty stomach, small white flakes began to be seen in about ten
or fifteen minutes, and the mixture soon assumed an opaque whitish
appearance. In an hour and a half the whole had disappeared. Two
drachms of albumen, mixed with two of gastric juice out of the stomach,
underwent the same changes, but in a rather longer time.
When the food is chiefly _liquid_, as when soup is taken either
alone or in large proportion, the more fluid part is speedily absorbed,
to fit the remaining nutritious portion for being better acted on by
the gastric juice and muscular power of the stomach; but in impaired
digestion, the requisite absorption of the fluid part does not go
on so rapidly. Fifty minutes after St Martin had dined on vegetable
soup, beef, and bread, Dr Beaumont found the stomach to contain a
pulpous mass, like thick gruel in consistence, and of a semi-gelatinous
aspect. The fluid portion had been absorbed to such an extent, that the
remainder was even thicker than is usual after eating more solid food.
From many similar observations, Dr Beaumont infers it to be a general
law, that soups and liquids cannot be digested till they are formed
into a thicker mass by the absorption of their watery part--as till
then they are too liquid to be easily acted on by the gastric juice.
Hence their unfitness for weak stomachs, and the impropriety of large
libations of tea or coffee at breakfast by persons whose digestion is
bad. During recovery from illness, chicken-tea, beef-tea, and soups,
are often useful, simply because the system then requires the liquid to
make up its lost blood.
Unfortunately Dr Beaumont made few experiments on the action of gastric
juice upon vegetables; and, in the few recorded, he generally contents
himself with noting the length of time required for their solution,
which generally proved considerably longer than for animal substances.
In one experiment, however, he states, that an hour after giving St
Martin nine ounces of _raw, ripe, sour, apples_, the stomach was
full of fluid and pulp, “quite acrid, and irritating the edges of the
aperture, _as is always the case when he eats acescent fruits or
vegetables_.” In an hour and a half the contents were still more
sharp and acrid, and the pulp of the apple visible. At the end of
two hours the stomach was empty, but the mucous membrane exhibited
an irritated appearance. With farinaceous vegetables, however, the
results were different. Thus, when a pint of thick, rich, boiled sago,
sweetened with sugar, was given, the whole was digested in less than
two hours, and there was neither acrimony of the gastric contents
nor smarting of the edges of the wound; on the contrary, it seemed
peculiarly grateful to the stomach, and rendered the mucous membrane
soft, uniform, and healthy. The same results followed a repetition
of the experiment, and also when a pint of soft custard was taken. In
some states of the stomach, it is true, even farinaceous food excites
acrimony and irritation, but rarely in the same degree as the other
forms of vegetable aliment.
* * * * *
Such being the influence of gastric juice on different aliments at
the natural heat of the body, we have now to ascertain, in the SECOND
place, what share the _high temperature_ has in the result.
To determine this point, Dr Beaumont took out two ounces of gastric
juice, and divided it into two equal portions, in separate vials. He
added to each an equal weight of masticated fresh beef; and placed the
one in a bath at the temperature of 99°, and the other in the open air
at 34°. As a contrast to these, he placed beside the latter a third
vial, containing the same weight of masticated meat in an ounce of
clear water.
In two hours the meat in the warm vial was partially digested; that in
the cold gastric juice was scarcely changed; and the third portion, in
the cold water, seemed only a little macerated. In six hours the meat
in the warm vial was half digested, while that in the two others had
undergone no farther alteration. The gastric juice in the first vial
having by this time dissolved as much as it could of the beef, four
drachms more were added from the stomach, and the vial was replaced in
the bath. _Digestion, which had previously ceased, was now resumed,
and went on as steadily as if it had not been interrupted_; thus
shewing, in a striking manner, the impropriety of exceeding in our
meals the quantity for which alone a sufficiency of gastric juice can
be provided.
At the end of twenty-four hours, the three portions were examined. That
contained in the warm juice was completely dissolved, and presented the
usual appearances. The portions contained in the cold juice and in the
cold water very much resembled each other, and exhibited no appearance
whatever of chyme. They were macerated or softened, but not digested.
These experiments, and others of a similar nature, shew clearly that a
temperature equal to ordinary blood-heat is requisite for chymification.
To make sure that it was the low temperature alone which prevented the
occurrence of digestion in the experiment detailed, Dr Beaumont now
placed the vial containing the meat which had been exposed without
effect for twenty hours to the action of the cold gastric juice on a
water-bath at the ordinary blood-heat. In a very short time “digestion
commenced, and advanced regularly as in the other parcels.” The same
results were always obtained from a repetition of these experiments,
so that they may be held as perfectly conclusive in establishing the
essentiality of heat to the digestive process. Common observation,
indeed, establishes this truth. Dr Kitchener, for example, after
stating that “a certain degree of heat is absolutely necessary to
excite and support a regular process of digestion,” remarks, that,
“when the circulation is languid and the food difficult of solution in
aged persons and invalids, even _external_ heat will considerably
assist concoction, and the application of the calefacient concave
(stomach warmer) will enable the digestive organs to overcome
refractory materials, and convert them into laudable chyle.”[30]
* * * * *
THIRDLY.--The necessity of _gentle_ and _continued agitation_ for
the accomplishment of digestion, is so obvious from the preceding
exposition, that it requires no direct experiments to establish it.
When portions of meat were suspended in the stomach, by a string so
short as to prevent them from being fully subjected to the motion
already described as always going on during digestion, _the action of
the gastric juice was confined almost entirely to their surface_, and a
longer time was consequently required for their solution than when they
were left at liberty. In like manner, when meat out of the stomach was
placed in a vial containing gastric juice, its solution was uniformly
accelerated by gentle agitation, which acted simply by removing the
coating of chyme as it formed on the surface, and thus affording to
the gastric fluid an easier access to the undigested portions below.
Accordingly, when in one of Dr Beaumont’s experiments two ounces
of unmasticated roasted beef were introduced through the external
aperture into the stomach, and held by a string, only one-half of it
was digested in four hours, evidently from the want of mastication
confining the action of the gastric juice to the surface of the mass,
and because the string prevented it from following the regular motions
of the stomach.
* * * * *
Having now made the reader sufficiently acquainted with the agents
concerned in, and the conditions essential to the performance of
digestion out of the body, we have next to exhibit the same agents
and the same conditions in their ordinary operation in the living
being, and to describe the beautiful arrangements by which they are
respectively and unerringly regulated.
It has been already shewn, that, in endowing us with appetite, Nature
has intended both to insure by its means a timely provision for the
wants of the system, and to guard against our eating more than enough
to supply them. We have also seen that, within certain limits, the
quantity of gastric juice secreted bears a direct relation to the
quantity of food consumed; that when the food exceeds considerably
the real necessities of the system, a part of it remains undigested,
because the stomach is unable to secrete a sufficiency of fluid for
the solution of the whole; and that, as a necessary consequence,
indigestion follows. This being the case, we may expect to find all
the arrangements of Nature made with a view to prevent us from hastily
filling the stomach to repletion, without being fully warned beforehand
of the error we are committing. And such accordingly is the fact.
Considered in this light, the processes of mastication insalivation,
and deglutition, are not only useful in preparing the morsel for
the future action of the gastric juice, but, by transmitting the
food to the stomach in small portions at a time, likewise serve
the important secondary purpose of _preventing its too rapid or
excessive distention_. To this good end, indeed, the stomach
itself contributes, as has been distinctly shewn by Dr Beaumont. In
the natural state of that organ, a regular and gentle contraction
of its whole fibres and cavity follows the introduction of each
individual morsel, and it is not till the relaxation consequent on
that contraction takes place, that another is willingly admitted.
This arrangement was more than suspected by other physiologists, but
it remained for the American experimenter to _demonstrate_ its
existence and purposes. It is true that, during a hurried repast for
example, food _may_ be rapidly introduced into the stomach by an
active effort of the will, but it is precisely in such circumstances
that we are apt to eat too much, and that indigestion follows; because,
from no time being allowed for the secretion of the requisite quantity
of gastric juice, and its proper mixture with each portion of the
aliment, the stomach is placed in an unnatural situation, and its
nerves cannot receive the same impression of “_enough eaten_,”
which is designed by Nature to arise only from the one being duly
proportioned to and mixed with the other. The advantage of the natural
arrangement is therefore confirmed rather than refuted by what may at
first appear an exception.
When Dr Beaumont depressed the valve in St Martin’s stomach, and
introduced a few spoonfuls of soup at the orifice, he observed the rugæ
or folds of the mucous membrane to close gently upon it, gradually
diffusing it through the gastric cavity, and completely preventing the
entrance of a second quantity till this diffusion was effected--when
relaxation again took place, and admitted of a farther supply. When
solid food was introduced in the same way, either in larger pieces
or finely divided, the same gentle contraction and grasping motion
were excited, and continued from fifty to eighty seconds, so as to
prevent more from being introduced without considerable force till the
contraction was at an end. When St Martin was so placed as to admit
of the cardia or upper orifice of the stomach being brought into view,
and was then made to swallow a morsel of food in the natural way, a
similar contraction of the stomach, and closing of its fibres upon the
bolus, was invariably observed to take place; and till this was over, a
second morsel could not be received without a considerable effort. And
accordingly, when, either from haste or hunger, we disregard the order
of Nature, and hurriedly gulp down food without due mastication, and
without allowing time for the regular contraction of the stomach, we
necessarily expose ourselves to the risk both of overloading it, and of
ultimately impairing its digestive power.
Such being the provision made for insuring the gradual admission of
food into the stomach, the next requisite is _its proper admixture
with the gastric juice_.
Food being the appropriate stimulus of the secreting vessels of the
stomach, the moment the alimentary morsel comes into contact with the
mucous membrane, the action of the latter, as was formerly pointed out,
becomes increased; its bloodvessels are distended, its colour deepens
to a brighter red, and the gastric juice immediately begins to be
poured out. The muscular fibres of the stomach, being acted upon by the
same stimulus, next come into play, and execute their specific function
of alternate contraction and relaxation. By these means the aliment
speedily becomes impregnated with the gastric fluid and undergoes the
influence of that continued gentle agitation already described as
essential to digestion, and which seems to have for its chief object
the careful admixture of every portion of the nutriment with the
quantity of gastric juice necessary for its solution. The particles
of food are thus continually changing place, and if the quantity taken
be not too great for the power of the gastric juice which the stomach
can supply, chymification goes on equally throughout; so that, if the
contents of the stomach be withdrawn in from thirty minutes to an hour
after a moderate meal, they will be found to consist of perfectly
formed chyme and particles of food, intimately mixed and blended, in
larger or smaller proportions, according to the vigorous or enfeebled
state of the digestive organs, and the quality of the aliment itself.
So effectually indeed has the admixture of food and solvent juice taken
place in this short time, that, as already shewn, when a portion is
removed from the stomach and placed in an appropriate vessel, digestion
will commonly continue in it, provided it be placed in a proper
temperature, and subjected to gentle and continued agitation.
It is the impossibility of its being adequately acted upon by the
muscular contractions of the stomach, which renders fluid and highly
concentrated nourishment, when exclusively used, so difficult of
digestion; and hence the reason why a certain bulk and consistence
given to whale oil, for example, by the admixture of such innutritious
substances as vegetable fibre, bran, or even saw-dust, make it a more
acceptable and digestible article of food to the inhabitants of the
northern regions, than when it is consumed in its pure state. In like
manner, in civilized society, bread, potatoes, and vegetables, are
useful, not less by giving the requisite bulk and consistence to the
rest of the food, than by the nutriment which they contain. Soups,
jellies, arrow-root, and similar substances, are, for the same reason,
more easily digested when eaten along with bread or some bulkier
aliment, than when taken alone, especially if used for some time.
The motion which we have seen to be excited in the stomach by the
entrance of aliment, is at first very gentle and slight; but in
proportion as digestion proceeds, or the organ is distended, it
becomes more rapid and energetic; and then it serves the additional
purpose of gradually propelling the chyme through the pylorus into
the intestine, there to be farther prepared and converted into chyle.
The necessary churning or agitation of the food is, from the peculiar
situation of the stomach, greatly assisted by the play of the diaphragm
and abdominal muscles during inspiration and expiration; and the
diminution of the vivacity and extent of the respiratory movement which
always attends despondency and grief, is one source of the enfeebled
digestion which notoriously accompanies or follows depression of mind.
The same cause also leads necessarily to an unfavourable condition of
the blood itself, which in its turn weakens digestion in common with
every other function; but the muscular or mechanical influence is that
which at present chiefly concerns us. On the other hand, the active
and energetic respiration attendant on cheerfulness and buoyance of
spirits, adds to the power of digestion, both by aiding the motions
of the stomach, and by imparting to it a more richly constituted
blood. If to these causes be added the increase of nervous stimulus
which pleasing emotions occasion in the stomach (as in the muscles,
and organs of secretion generally), we shall have no difficulty in
perceiving why digestion goes on so well in parties where there is much
jocularity and mirth. “Laughter,” says Professor Hufeland of Berlin,
“is one of the greatest helps to digestion with which I am acquainted;
and the custom prevalent among our forefathers, of exciting it at table
by jesters and buffoons, was founded on true medical principles. In a
word, endeavour to have cheerful and merry companions at your meals:
what nourishment one receives amidst mirth and jollity will certainly
produce good and light blood.”[31]
Exposed to the action of all the agents above enumerated, and to the
increased nervous and vascular excitement which are necessary during
digestion, a singular change soon commences in the food, and goes on
till chymification is completed. After a little while the contents
of the stomach, whatever their nature and variety, begin to be
converted into a substance of a homogeneous, soft, greyish, and viscid
appearance, of a sweetish, _fade_, and slightly acid taste, but
which still preserves some of the qualities of the food, and is called
chyme. The chyme always forms on that part of the food with which the
gastric juice is in immediate contact; and, in proportion as it is
produced, it is carried gradually onwards by the gentle motion of the
stomach towards the pylorus, where consequently it always exists in the
greatest quantity. At the cardiac or left end of the stomach it is most
sparingly found, both because digestion is there only beginning, and
because the chyme is speedily removed from it and carried away towards
the pylorus.
The doctrine hitherto generally received, and held by Dr Wilson Philip
and others as demonstrated, is, that “the layer of food lying next to
the surface of the stomach is first digested, and in proportion as this
undergoes the proper change, and is moved by the muscular action of the
stomach, that next in turn succeeds, to undergo the same change.” Dr
Beaumont, however, declares, that, whatever may be the case in rabbits
and other animals on which Dr Philip’s experiments were made, such was
not the order observed in the stomach of Alexis St Martin--and such,
he naturally infers, is not the order in the human stomach in general.
Nor is such, I may add, the order which either experience or a correct
view of the antecedent circumstances and physiological conditions
ought to lead us to anticipate. When vomiting, for instance, occurs an
hour or two after a meal composed of different ingredients has been
swallowed, no such separation into digested and undigested portions
is to be found, but the whole are observed to have undergone changes
proportioned to their degrees of digestibility, whether they were eaten
first or last.
In conformity with this view, Dr Beaumont mentions, that, when St
Martin swallowed a mouthful of any tenacious food after the digestion
of the preceding meal was considerably advanced, he always saw it
first pass towards the great curvature of the stomach, and then
disappear. In a minute or two it re-appeared, more or less broken down,
and _mixed with the general alimentary mass_; and in a short
time longer it was so much changed as entirely to lose its identity.
From these and numerous other facts, Dr Beaumont infers, that “there
is a perfect admixture of the whole ingestæ during the period of
alimentation and chymification;” and that “the whole contents of the
stomach until chymification be nearly complete, exhibit a heterogeneous
mass of solids and fluids--hard and soft, coarse and fine, crude and
chymified--all intimately mixed, and circulating promiscuously through
the gastric cavity, like the mixed contents of a close vessel, gently
agitated or turned in the hand.” (P. 112.) As we proceed we shall meet
with various indirect proofs of these statements being correct.
If Dr Beaumont’s observations on this subject are accurate, we may
expect to find that chymification commences _on the surface of each
individual fragment_ of the food, and is not confined to the outer
surface of the entire alimentary mass, as stated by Dr Philip. Such,
accordingly, is the fact. When Dr Beaumont extracted a portion of the
food through the opening half an hour or an hour after eating, he
invariably found it composed of perfectly formed chyme and particles
of food intimately mixed and blended; and in these experiments every
portion of the aliment was already so completely supplied with gastric
juice, that its chymification proceeded till the whole was digested
with no other aid than that of the requisite heat and agitation.
When a meal is taken before the preceding one is out of the stomach,
digestion is observed to be disturbed. Dr Wilson Philip explains
this by stating, that the newly swallowed food becomes imbedded in,
and occupies the centre of, the older and half-digested mass, where
it remains distinct and untouched till the former meal is entirely
disposed of. A more logical explanation, however, and one more in
harmony with facts, is offered by Dr Beaumont, who ascribes the
disturbed digestion to _the supply of gastric juice having been
entirely taken up by the first meal_, and to the stomach, now
comparatively exhausted, being unable to secrete a fresh supply for the
second--seeing that, in ordinary circumstances, its vessels secrete
only enough to meet the real wants of the system. Dr Beaumont adduces
in confirmation of this view, the fact that many children, and most
cooks, are in the habit of eating _small_ quantities of food
almost every hour or two without their digestion suffering materially,
because then the amount of gastric juice secreted is quite equal to the
chymification of the _whole_ quantity taken.
Reasonable as this inference appears from the facts stated by Dr
Beaumont, I cannot help thinking that there is something more in the
constitution of the stomach than the mere deficiency of gastric juice,
which renders the too early intrusion of new food hurtful. We know,
for example, that, at the commencement of digestion, the muscular
contractions of the stomach are comparatively slow and feeble, and
that as chymification advances they become rapid and energetic, as
if to remove the chyme as fast as it is formed. If then new food,
for which the feebler movement is best adapted, be introduced when
digestion is far advanced and the energetic motion going on, may not
this disproportion be itself an impediment, and co-operate with the
deficiency of the gastric juice in disordering digestion? Moreover, as
the stomach, in common with every other organ intended for alternate
activity and repose, is always more or less fatigued by the active
fulfilment of its function, its premature excitement by new food must
add to its exhaustion, and weaken its power (in the same way in which
fresh muscular exertion adds to the exhaustion of muscles already
sufficiently exercised), and consequently lead to imperfect digestion.
The same principle which explains the necessity of repose for repairing
the vascular and nervous energy of the stomach, when these have been
excited and exhausted by the labour of digestion, also affords a
solution of the question why the appetite does not return as soon as
the stomach is empty, but begins to be felt only after the latter has
enjoyed a period of repose, varying in duration with the mode of life,
the state of health, and the nature of the previous meal.
If we regard chymification as going on at the surface of every
individual portion of the food, we at once see that the constant motion
of the stomach serves, not only to affect the original mixture of the
food with the gastric juice, but to remove the chyme from the surface
of each little fragment of the alimentary mass in proportion as it
is formed, and by this very removal to expose a fresh surface of the
fragment to the contact of the mucous membrane, thereby enabling it to
excite a farther secretion of the gastric juice, where, as sometimes
happens, the stomach is unable to provide a sufficient quantity from
the beginning. In this way the formation and removal of chyme go on
from the very first, although, of course, more slowly than after the
gastric solvent has had time to act. It is generally said that an hour
elapses before any chyme is formed; but Dr Beaumont has detected its
existence at a much earlier period, and is of opinion that, from the
uniform and constant decrease in the contents of the stomach, which
begins as soon as the food is swallowed, chymification commences almost
immediately. This decrease, though slow at first, becomes gradually
accelerated, till the whole mass is converted into chyme. Apparently
in harmony with this more energetic action, the acidity of the gastric
fluid also becomes greater, and affords a greater stimulus, in
proportion as digestion advances.
As formerly explained, the thickish, semi-fluid, greyish, chyme, into
which the aliment is converted, is gradually impelled towards the
pyloric extremity of the stomach. On its arrival there, the pylorus, or
valve between the stomach and the intestine called the _duodenum_,
opens and allows the chyme to pass into the intestine. But, by a
curious mode of sensibility, if any portion of undigested food be mixed
with it, the pylorus contracts upon it, refuses it egress, and throws
it back into the stomach for farther digestion.
If, however, any thing really indigestible finds its way into the
stomach, and presents itself at the pylorus--or if the stomach has
temporarily lost its digestive power, and the food remains in it for
many hours unchanged--then the pylorus, after repeatedly refusing
egress, at last opens and allows it to pass into the gut. So marked is
the contractile impulse towards the pylorus when digestion is going on,
that Dr Beaumont found even the bulb of his thermometer carried down
with a steady and considerable force.
Such are the _direct_ conditions requisite for the fulfilment of
digestion: but there remain others, of an _indirect_ kind, which
also require to be noticed. Of these, a due supply of arterial blood
and nervous energy is the most remarkable; but as both produce their
effect by modifying the secretions and motions of the stomach, already
described as the _direct_ requisites of digestion, it will save a
good deal of repetition if, for the present, we take their influence
for granted, and reserve their further elucidation till we come to
treat of the practical applications of the preceding exposition.
* * * * *
Having thus obtained a comprehensive view of the agents employed in
effecting digestion, and of the changes produced by it on different
kinds of food, we find another important subject of investigation,
immediately connected with the process, presenting itself--_the
comparative digestibility of different kinds of food_. Dr Beaumont
did not neglect this branch of the inquiry; but the experiments which
he performed for its elucidation are, like those of most of his
predecessors, deprived of great part of their value by the vague way in
which they seem to have been conducted, and the common omission of all
particulars in regard to those conditions which are known to exert a
powerful influence on the progress of digestion.
The following Table, which I have arranged in a more lucid order
than Dr Beaumont has done, exhibits the general results of all the
experiments made upon St Martin posterior to 1825; and the average is
deduced from those which were performed when the stomach was considered
by Dr Beaumont to be in its natural state, and St Martin himself
subjected to ordinary exercise.
_TABLE shewing the Mean Time of Digestion of the different
Articles of Diet._
|---------------------------|-----------------|---------------|
| | Mode | Time required |
|Articles of Diet. | of | for |
| | Preparation. | Digestion. |
|---------------------------|-----------------|---------------|
| | | H. M. |
| Rice | Boiled | 1 |
| Pig’s feet, soused | Boiled | 1 |
| Tripe, soused | Boiled | 1 |
| Eggs, whipped | Raw | 1 30 |
| Trout, Salmon, fresh | Boiled | 1 30 |
| Trout, Salmon, fresh | Fried | 1 30 |
| Soup, barley | Boiled | 1 30 |
| Apples, sweet and mellow | Raw | 1 30 |
| Venison steak | Broiled | 1 35 |
| Brains | Boiled | 1 45 |
| Sago | Boiled | 1 45 |
| Tapioca | Boiled | 2 |
| Barley | Boiled | 2 |
| Milk | Boiled | 2 |
| Liver, beef’s, fresh | Broiled | 2 |
| Eggs, fresh | Raw | 2 |
| Codfish, cured, dry | Boiled | 2 |
| Apples, sour and mellow | Raw | 2 |
| Cabbage, with vinegar | Raw | 2 |
| Milk | Raw | 2 15 |
| Eggs, fresh | Roasted | 2 15 |
| Turkey, wild | Roasted | 2 18 |
| Turkey, domestic | Boiled | 2 25 |
| Gelatine | Boiled | 2 30 |
| Turkey, domestic | Roasted | 2 30 |
| Goose | Roasted | 2 30 |
| Pig, suckling | Roasted | 2 30 |
| Lamb, fresh | Broiled | 2 30 |
| Hash, meat and vegetables | Warmed | 2 30 |
| Beans, pod | Boiled | 2 30 |
| Cake, sponge | Baked | 2 30 |
| Parsnips | Boiled | 2 30 |
| Potatoes, Irish | Roasted | 2 30 |
| Potatoes, Irish | Baked | 2 30 |
| Cabbage, head | Raw | 2 30 |
| Spinal marrow | Boiled | 2 40 |
| Chicken, full grown | Fricassee | 2 45 |
| Custard | Baked | 2 45 |
| Beef, with salt only | Boiled | 2 45 |
| Apples, sour and hard | Raw | 2 50 |
| Oysters, fresh | Raw | 2 55 |
| Eggs, fresh | Soft boiled | 3 |
| Bass, striped, fresh | Broiled | 3 |
| Beef, fresh, lean, rare | Roasted | 3 |
| Beef, steak | Broiled | 3 |
| Pork, recently salted | Raw | 3 |
| Pork, recently salted | Stewed | 3 |
| Mutton, fresh | Broiled | 3 |
| Mutton, fresh | Boiled | 3 |
| Soup, beans | Boiled | 3 |
| Chicken soup | Boiled | 3 |
| Aponeurosis | Boiled | 3 |
| Cake, corn | Baked | 3 |
| Dumpling, apple | Boiled | 3 |
| Oysters, fresh | Roasted | 3 15 |
| Pork-steak | Broiled | 3 15 |
| Pork, recently salted | Broiled | 3 15 |
| Mutton, fresh | Roasted | 3 15 |
| Bread, corn | Baked | 3 15 |
| Carrot, orange | Boiled | 3 15 |
| Sausage, fresh | Broiled | 3 20 |
| Flounder, fresh | Fried | 3 30 |
| Catfish, fresh | Fried | 3 30 |
| Oysters, fresh | Stewed | 3 30 |
| Beef, fresh, dry | Roasted | 3 30 |
| Beef, with mustard, &c. | Boiled | 3 30 |
| Butter | Melted | 3 30 |
| Cheese, old, strong | Raw | 3 30 |
| Soup, mutton | Boiled | 3 30 |
| Oyster soup | Boiled | 3 30 |
| Bread, wheaten, fresh | Baked | 3 30 |
| Turnips, flat | Boiled | 3 30 |
| Potatoes, Irish | Boiled | 3 30 |
| Eggs, fresh | Hard boiled | 3 30 |
| Eggs, fresh | Fried | 3 30 |
| Green corn and beans | Boiled | 3 45 |
| Beet | Boiled | 3 45 |
| Salmon, salted | Boiled | 4 |
| Beef, fresh, lean, | Fried | 4 |
| Veal, fresh | Broiled | 4 |
| Fowls, domestic | Boiled | 4 |
| Fowls, domestic | Roasted | 4 |
| Ducks, domestic | Roasted | 4 |
| Soup, beef, vegetables, | Boiled | 4 |
| and bread | | |
| Heart, animal | Fried | 4 |
| Beef, old, hard, salted | Boiled | 4 15 |
| Pork, recently salted | Fried | 4 15 |
| Soup, marrow bones | Boiled | 4 15 |
| Cartilage | Boiled | 4 15 |
| Pork, recently salted | Boiled | 4 30 |
| Veal, fresh | Fried | 4 30 |
| Ducks, wild | Roasted | 4 30 |
| Suet, mutton | Boiled | 4 30 |
| Cabbage, with vinegar | Boiled | 4 30 |
| Suet, beef, fresh | Boiled | 5 30 |
| Pork, fat and lean | Roasted | 5 15 |
| Tendon | Boiled | 5 30 |
|---------------------------|-----------------|---------------|
This table is very interesting, but the results must not be too much
relied upon, or regarded as representing the _uniform_ rate of
digestibility. We have already seen that chymification is greatly
influenced by the interval which has elapsed since the preceding meal,
the amount of exercise taken, the keenness of the appetite, the state
of the health and mind, the completeness of the mastication, the state
of rest or exercise after eating, and various other circumstances;
and, above all, _the quantity swallowed in proportion to the gastric
juice secreted_. And consequently, if an experiment be made without
regard to these conditions, and without any thing being recorded
except the time occupied in digestion in the individual case, the
conclusions deduced from it may be most fallacious. The very aliment
which, taken in full quantity, remains on the stomach for hours, may,
in a smaller quantity, be entirely digested in one-third of the time.
Thus, in the foregoing table, two and a half hours are set down as the
average period required for the chymification of jelly; and yet, in
one of Dr Beaumont’s experiments, we find that eight ounces of that
substance were entirely digested in ONE hour. So that, if all the other
conditions are not carefully kept in view at each trial, the results
cannot possibly be held as conclusive.
It may be said that, on the occasion just alluded to, St Martin’s
digestion must have been particularly good--and, in truth, it seems
to have been so; for at nine o’clock A. M. he breakfasted
on _soused tripe, pig’s feet, bread and coffee_, and yet, only
_one_ hour later, no vestige of any of these savoury things
remained in the stomach. What renders this result the more remarkable,
is the fact, that, in another table, a simple breakfast of coffee
and bread is set down as having required FOUR hours for its
digestion. The rapid disposal of the same elements with the addition
of soused tripe and pig’s feet, instead of disproving my position,
evidently strengthens it, by shewing that, if _from any cause_
the digesting power varies in intensity, the result obtained from
the experiment on one kind of food, cannot, with any shew of reason,
be considered as an accurate index of its rate of digestibility in
comparison with that of other kinds.
This neglect of the other conditions is accordingly the circumstance
which throws a doubt over the results not only of Dr Beaumont’s
experiments, but of those of every other inquirer. Dr Beaumont
indeed candidly admits, that his were performed for the purpose of
demonstrating other important principles connected with digestion,
and not at all with the view of determining the comparative rates of
digestibility of different kinds of aliment; and in alluding to the
various requisites for a satisfactory series of experiments, he himself
justly states, that this would be a Herculean task which it would take
years to accomplish. In considering the following general results,
then, the reader ought to bear in mind that they are only probable and
approximative, and not strictly demonstrated or certain.
* * * * *
As a general rule, animal food is more easily and speedily digested,
contains a greater quantity of nutriment in a given bulk, and
therefore satisfies hunger for a longer time, than either herbaceous
or farinaceous food; but, apparently from the same cause, it is also
more heating and stimulating. _Minuteness of division_, and
_tenderness of fibre_, are shewn by Dr Beaumont’s experiments to
be two grand essentials for the easy digestion of butcher-meat; and
the different kinds of fish, flesh, fowl, and game, are found to vary
in digestibility chiefly in proportion as they approach or depart from
these two standard qualities.
Farinaceous food, such as rice, sago, arrow-root or gruel, is also
rapidly assimilated, and proves less stimulating to the system than
concentrated animal food; but as it affords no scope for the due action
of the muscular coat of the stomach, its exclusive use for any length
of time seldom fails to weaken that organ and impair digestion. For
the same reason, however, it becomes a very appropriate aliment, where
stomachic irritation already exists. When the stomach is in a healthy
state, milk is digested almost as easily as farinaceous food and is
equally unstimulating.
The other kinds of vegetable substance are the slowest of all in
undergoing digestion, and very frequently pass out of the stomach
and through the bowels comparatively little changed; and hence the
uneasiness which their presence so often excites in the intestinal
canal, especially in persons of weak digestion, owing to the nerves of
the intestines having a relation to _chyme_ or _digested_
food, and not to substances which resist the action of the gastric
juice. In a given bulk they contain less nutriment, and excite the
system less, than any other kind of food; so that they are well adapted
for the diet of those in whom it is necessary to avoid every kind of
stimulus, and who are not subjected to great muscular exertion; but to
a person undergoing hard labour, they afford inadequate support.
Liquids--soup, for example--do not call into play the muscular coat of
the stomach, and are so slow of digestion where that organ is already
weakened, that they often give rise to acidity; and hence they are
unfit for most dyspeptic patients. Before the gastric juice can act
upon them, the fluid part must be absorbed, and the mass thickened to
a proper consistence for undergoing the usual _churning_ motion.
On examining the contents of the stomach an hour after St Martin
had dined on beef-soup, Dr Beaumont found that on one occasion the
absorption of the watery part had been carried so far as to leave the
remainder of even a thicker consistence than after an ordinary solid
meal, but a similar result follows only when the digestive powers
are very vigorous. When drink is swallowed, it also is carried off by
absorption, and is not digested or allowed to pass through the pylorus.
One purpose of this provision seems to be to prevent the gastric juice
from being rendered inefficient by too much dilution.
When the food on which an animal lives is of a highly concentrated
kind, and contains much nourishment in a small bulk, the apparatus of
organs provided for its digestion is on a correspondingly small scale
in point of extent. Thus, in carnivorous animals, whose food is, bulk
for bulk, the most nutritious of all, the stomach and intestines are
simple and short, the latter not exceeding in length more than from
one to four or five times that of the body. In herbivorous animals,
on the other hand, whose food is sparingly nutritious, and therefore
requires to have a large bulk or volume, the stomach, as we saw in a
former chapter, is greatly more complicated, and the length of the
intestines enormously increased. Man, being intended to feed on both
animal and vegetable substances, possesses an organization which holds
an intermediate place between the two extremes. In him neither are
the intestines so short as in carnivorous animals, nor have they the
complexity and length characteristic of the herbivorous--thus clearly
shewing the intentions of Nature in regard to his food, and at the same
time allowing him a considerable latitude of adaptation when the force
of circumstances for a time denies him access to any variety.
Animal food being in general more quickly digested than vegetable, and
a simpler organization being sufficient for its conversion into chyme,
many physiologists have inferred that this is owing solely to its
being already of an animal nature, and therefore requiring scarcely any
change to fit it for becoming a constituent part of the living fibre.
But I agree with Dr Beaumont in thinking that this explanation is more
gratuitous than philosophical, and that the process of chymification
implies almost as complete a change in the one instance as in the
other. In both, the operation of the gastric juice seems to be entirely
analogous. In both, a complete solution takes place, and the chyle
into which animal food is ultimately converted bears no greater
resemblance to the future animal fibre, than does that produced from
vegetable aliment. Thus the chyle of a horse, which lives exclusively
on vegetables, has quite as great a resemblance to its future muscle,
as that of a tiger, a lion, or a fox has to _its_ future produce.
Besides, whether the food be animal or vegetable, the ultimate result
of digestion is always the formation of _new animal matter_;
but in the former case, the nutritive particles are mixed up with a
smaller proportion of innutritious matter than in the latter, and
consequently a larger quantity of them can be extracted from a given
bulk in a shorter time, than in the case of vegetables. There are most
probably also minute differences in the chemical composition of the
chyle derived from different kinds of food; but its general nature--its
fitness for forming new animal tissue--and that of the process by which
it is produced, are always the same.
Animal food, it is true, affords a more stimulating nutriment than
farinaceous and other kinds of vegetable aliment, and hence it is
avoided in diseases of excitement. But it seems to me that this
stimulus is owing not only to its own inherent properties, but also to
its more highly concentrated state, and to the much greater quantity
of chyle which is derived from it than from an equal bulk of vegetable
aliment. From the numerous experiments of injecting water, poisons, and
other substances into the veins, performed by Magendie and others, we
have direct proofs that the same agent which, introduced rapidly into
the system, will sometimes act so powerfully as to destroy life, will
excite scarcely any perceptible disorder if introduced very slowly,
Analogy, therefore, bears us out in believing that the rapid admixture
of very nutritious chyle with the blood may over-stimulate the system,
when its more gradual introduction would have produced no such effect.
At the same time, there can be no doubt that there is also a greater
inherent stimulus in animal than in vegetable aliment.
It seems to be partly for the purpose of obviating the evil of the too
rapid introduction of nutriment, and partly for that of varying the
stimulus, that Nature has rendered a certain bulk of food advantageous
to digestion, and decreed that no animal can long retain its health if
fed on highly concentrated aliment alone. Dogs fed on oil or sugar,
which are almost wholly converted into chyle, become diseased and
die in a few weeks; and, as Dr Paris has acutely remarked, the very
capacity of our digestive organs is a proof that Nature never intended
them for the exclusive reception of highly concentrated food. Dr Paris
refers to post-horses fed chiefly on beans and corn, as instances among
the lower animals of the insalubrity of too condensed nutriment, and
shews that they live constantly on the brink of active disease, and
every now and then require bleeding, laxatives, and emollients, to keep
them in condition. Sportsmen, boxers, and others, who train themselves
for severe exertion, are additional examples shewing that a similar
mode of living induces a morbid tension of the system which cannot be
long kept up without danger. The Kamtschatdales sometimes live with
impunity for months on fish-oil, by wisely mixing it up with saw-dust
or other indigestible vegetable fibre, which has the double advantage
of diluting the food, and of affording due scope for the action of the
muscular coat, and thus placing the food in more perfect harmony with
the constitution of the stomach.
If the preceding explanation of the more rapid digestion of animal than
of vegetable substances, and the higher stimulus which they afford be
correct, the common notion of the former being more digestible than
the latter _solely_ because there is a greater analogy between
animal food and the system which it goes to nourish, and therefore a
smaller change to be undergone, necessarily falls to the ground. If
it be true--which it seems to be--that, _in the natural state_,
in a temperate climate, animal food is more easily digested than
vegetable, the fair inference ought rather to be that the system
requires the former in larger proportion than the latter, and that
the gastric juice is purposely constituted with reference to this
circumstance. Accordingly, in the Arctic Regions, where the climate
renders great stimulus necessary, animal food, of to us the most
indigestible kind--that consisting of pure fat and oil--is eaten in
immense quantities and digested with enviable facility; while in India
and other tropical climates, where much less stimulus is required,
the natives digest vegetable aliment with at least equal ease and
satisfaction.
If, as Dr Paris imagines, animal food owes its digestibility simply to
its possessing “a composition analogous to that of the structure which
it is designed to supply,” and therefore requiring “little more than
division and depuration,” instead of the alleged “complicated series
of decompositions and recompositions, which must be effected before
vegetable matter can be animalized or assimilated to the body,”[32]--it
follows that butcher-meat must in all climates and situations be more
digestible than vegetables; and that _raw_ meat, which has the
greatest analogy of all to the structure of the body, must require
still less digestive power for its solution and assimilation than
cooked meat. These propositions, however, are wholly at variance with
experience: in particular, the effect of cooking is unquestionably to
induce a change of composition subversive of the analogy on which Dr
Paris rests his opinion.
That the easier digestibility of animal food in man arises chiefly from
its greater adaptation to the qualities of the gastric juice, and not
from any such analogy as that now alluded to, is rendered still more
probable by the fact, that in him the gastric fluid contains scarcely
any free acid, except where the diet has consisted for some time
principally of vegetables; whereas it always contains a considerable
proportion of acid in herbivorous creatures. In the latter, moreover,
the analogy is quite as great between animal substances and their own
structure as in man, and yet to a cow, beef is much more indigestible
than grass, notwithstanding the “decompositions and recompositions”
which the latter is supposed to require before becoming animalized. Dr
Beaumont is therefore quite justified in maintaining, that the process
of digestion implies as complete a solution and recomposition in the
case of animal as of vegetable substances; and that the rapidity with
which the chymification of either is effected _depends more on its
adaptation to the properties of the gastric juice provided by Nature
for its solution, than on the closeness of resemblance of its own
composition to that of the body of which it is to become a part_.
Another prevalent notion--that the digestive apparatus is simpler and
shorter in carnivorous than in herbivorous animals, merely because
their food is more analogous in composition to their own bodies,
and therefore requires less perfect digestion--seems to me equally
unfounded, and to be negatived by the fact, that, in the grain-eating
birds, in the constituent elements of whose food there is no such
analogy, the intestines nevertheless scarcely exceed in length those of
carnivorous birds--a circumstance at variance with the notion of length
being necessary _solely_ on account of the great elaboration
required for the conversion of vegetable into animal substance.
The true principle--and it is important to notice it, as the error
is generally adopted--appears to be, that _where the food of the
animal contains much nutriment in a small bulk, there the stomach and
intestinal canal are simple and short_; but where, on the contrary,
it contains little nutriment in a large bulk, there great capacity,
complexity, and length become requisite to enable the animal to
elaborate a sufficiency of nourishment for its subsistence, by taking
in the requisite quantity from which it is to be derived. Accordingly,
in the elephant and some other herbivorous animals we find the capacity
to depend not on the length, but on the width and increased surface
of the intestine, or, in other words, on the greater calibre of its
cavity; whereas, in some fishes which live on very concentrated
aliment, the intestinal canal is not much more than the length of the
body--thus shewing that the common opinion on the subject is utterly
untenable.
* * * * *
Before concluding his experiments on the agents employed in digestion,
Dr Beaumont made many observations with a view to ascertain whether
any increase of temperature occurs during that process. By introducing
a thermometer with a long stem at the external opening into St
Martin’s stomach, both before and during chymification, he succeeded
in obtaining very accurate information on this point. In two or three
of the experiments the heat of the stomach seemed to be increased
after taking food, but in by far the greater number the temperature
remained the same. It appears, however, that the variations of the
atmosphere produce a sensible change on the heat of the stomach--a dry
air increasing and a moist air diminishing it. The ordinary temperature
may be estimated at 100° Fahr., and in several instances it was higher
at the pyloric than at the cardiac end. On one cloudy, damp, and rainy
day, the thermometer rose only to 94°, and on another to 96°; whereas
next day, when the weather was clear and dry, it rose to 99°, and on
that following, when the weather was both clear and cold, to 100°. On
several occasions it rose as high as 102°, and once to 103°; but these
were after exercise, which was always observed to cause an increase
of two or three degrees. We have already seen that _artificial_
digestion is entirely arrested by cold, and is resumed on raising the
temperature to ordinary blood heat.
* * * * *
Such, then, are the phenomena and conditions of healthy digestion, and
such is the light thrown upon them both by the valuable publication of
the American physiologist. Before leaving this branch of the subject,
however, it may be useful to lay before the reader, as a kind of
summary, the principal inferences deduced by Dr Beaumont from his
numerous experiments and observations. But in doing so I shall attempt
to arrange the results in their natural order; for in the original work
they are given without reference either to logical sequence or to time.
INFERENCES FROM DR BEAUMONT’S EXPERIMENTS AND
OBSERVATIONS.[33]
1. That _hunger_ is the effect of _distention_ of the vessels
that secrete the gastric juice.
2. That the processes of _mastication_, _insalivation_, and
_deglutition_, in an abstract point of view, do not in any way
affect the digestion of the food; or, in other words, when food
is introduced directly into the stomach in a finely divided
state, without these previous steps, it is as readily and as
perfectly digested as when they have been taken.
3. That _saliva_ does not possess the properties of an
alimentary solvent.
4. That the _agent_ of chymification is the _gastric juice_.
5. That the pure gastric juice is fluid, _clear and
transparent_; without _odour_; a little salt; and perceptibly
_acid_.
6. That it contains free _muriatic acid_, and some other active
_chemical_ principles.
7. That it is never found _free_ in the gastric cavity; but is
always excited to discharge itself by the introduction of _food_
or other irritants.
8. That it is secreted from vessels distinct from the mucous
follicles.
9. That it is seldom obtained pure, but is generally mixed with
mucus, and sometimes with saliva. When pure it is capable of
being kept for months, and perhaps for years.
10. That it _coagulates_ albumen, and afterwards _dissolves_ the
_coagulæ_.
11. That it _checks_ the progress of putrefaction.
12. That it acts as a _solvent_ of food, and alters its
properties.
13. That, like other chemical agents, it _commences_ its action
on food as soon as it comes in contact with it.
14. That it is capable of combining with a certain and fixed
_quantity_ of food, and when more aliment is presented for its
action than it will dissolve, disturbance of the stomach, or
“indigestion,” will ensue.
15. That its action is facilitated by the _warmth_ and _motions_
of the stomach.
16. That it becomes intimately _mixed_ and _blended_ with the
ingestæ in the stomach by the motions of that organ.
17. That it is _invariably_ the _same substance_, modified only
by _admixture_ with other fluids.
18. That the motions of the stomach produce a constant
_churning_ of its contents, and _admixture_ of food and gastric
juice.
19. That these motions are in two directions, _transversely_ and
_longitudinally_.
20. That _no other_ fluid produces the same effect on food that
gastric juice does; and that it is the _only solvent of aliment_.
21. That the action of the stomach and its fluids is the same on
_all kinds_ of diet.
22. That _solid_ food, of a certain texture, is easier of
digestion than _fluid_.
23. That _animal_ and _farinaceous_ aliments are more easy of
digestion than _vegetable_.
24. That the susceptibility of digestion does not, however,
depend altogether upon _natural_ or _chemical_ distinctions.
25. That digestion is facilitated by _minuteness of division_
and _tenderness of fibre_; and retarded by opposite qualities.
26. That the _ultimate principles_ of aliment are always the
same, from whatever food they may be obtained.
27. That _chyme_ is _homogeneous_, but variable in its _colour_
and _consistence_.
28. That, towards the _latter_ stages of chymification, it
becomes more _acid_ and _stimulating_, and passes more rapidly
from the stomach.
29. That the _inner coat_ of the stomach is of a pale _pink_
colour, varying in its hues, according to its full or empty
state.
30. That, in health, it is sheathed with mucus.
31. That the appearance of the interior of the stomach, _in
disease_, is essentially different from that of its _healthy_
state.
32. That stimulating _condiments_ are injurious to the healthy
stomach.
33. That the use of _ardent spirits always_ produces disease of
the stomach if persevered in.
34. That _water_, _ardent spirits_, and most other _fluids_, are
not affected by the gastric juice, but pass from the stomach
soon after they have been received.
35. That the _quantity_ of food generally taken is more than the
wants of the system require; and that such excess, if persevered
in, generally produces not only functional aberration, but
disease of the coats of the stomach.
36. That _bulk_ as well as _nutriment_ is necessary to the
articles of diet.
37. That _bile_ is not ordinarily found _in the stomach_, and is
_not_ commonly _necessary_ for the digestion of the food; but,
38. That when _oily_ food has been used it assists its digestion.
39. That _oily_ food is difficult of digestion, though it
contains a large proportion of the nutrient principles.
40. That the _digestibility_ of aliment does not depend upon the
_quantity_ of nutrient principles that it contains.
41. That the natural temperature of the stomach is about 100°
Fahrenheit.
42. That the temperature is _not elevated_ by the ingestion of
food.
43. That _exercise elevates_ the temperature; and that _sleep_
or _rest_, in a recumbent position, _depresses_ it.
44. That _gentle exercise_ facilitates the digestion of food.
45. That the time required for that purpose is various,
depending upon the quantity and quality of the food, state of
the stomach, &c.; but that the time ordinarily required for the
disposal of a moderate meal of the fibrous parts of meat, with
bread, &c.; is from three to three and a half hours.
A few more inferences are given, but are here omitted because they
refer exclusively to the _chyle_, which has not yet been treated
of. The first is probably erroneous, and the second and seventeenth
are, perhaps, too strongly expressed. A complete change of diet, for
example, causes _some_ variation in the gastric juice, although
the latter inference, taken in a literal sense, affirms the contrary.
CHAPTER IV.
CHYLIFICATION, AND THE ORGANS CONCERNED IN IT.
Chylification--Not well known.--Organs concerned in it.--The
intestinal canal--Its general structure.--Peritoneal
coat--Mesentery--Muscular coat--Uses of these.--Air in
intestines--Uses of.--Mucous coat--Analogous to skin--The
seat of excretion and absorption--Mucous glands--Absorbent
vessels--Course of chyle towards the heart.--Nerves of mucous
coat.--Action of bowels explained.--Individual structure
of intestines--The Duodenum--Jejunum--and Ileum.--Liver
and pancreas concerned in chylification--Their situation
and uses.--Bile, its origin and uses.--The pancreas--Its
juice--The jejunum described--The ileum--Cœcum--Colon--and
Rectum.--Peristaltic motion of bowels--Aids to it.--Digestion
of vegetables begins in stomach but often finished in the
bowels.--Illustration from the horse--Confirmation by Dupuytren.
The conversion of food into chyme, an operation which, as we have
seen, takes place in the stomach, is only one of the series of changes
which aliment undergoes before becoming fit to be assimilated with
the living body; and the next process which we have to notice is
_chylification_, or that by which _chyme_ is converted into
_chyle_.
In proportion as chyme is formed from the food, it is gradually
propelled, as already shewn, through the pyloric orifice of the stomach
into the _duodenum_ or beginning of the small intestine. On its
arrival there, it is acted upon by the _bile_ from the liver,
and the _pancreatic juice_ from the pancreas; and the result
is the separation of the chyme into two distinct substances,--the
one a milky-white fluid called _chyle_, which is absorbed into
the system, and forms nutriment,--and the other a yellowish and more
consistent mass, which is the indigestible remains of the food, and
which, after traversing the whole length of the intestinal canal, and
being there mixed with the waste matter separated from the blood in
order to be thrown out of the system through the same channel, is at
last expelled in the form of _fæces_ or excrement.
If physiologists experience much difficulty in satisfactorily
explaining all the phenomena of _chymification_ or _stomach-digestion_,
the reflecting reader will not be surprised to learn that they are
still more puzzled to account for those of chylification or _intestinal
digestion_. The organs concerned in the latter are so deep-seated
and inaccessible during life, that very few opportunities occur of
obtaining accurate information on the subject; and, therefore, in what
follows, I shall not enter into disputed or intricate details, but
confine myself to such general views as are not contested, and as the
reader may easily understand. Fortunately, ignorance of this branch
of the inquiry is of less practical importance than if it extended
to stomachic digestion also; because such is the harmony between
all the parts of the system, that whatever conduces to the perfect
accomplishment of the first stage of the process, _chymification_, is
in so far equally conducive to the proper fulfilment of _chylification_
or intestinal digestion.
The simple fact, indeed, of our having no _direct_ control over
the process of chylification, and of our being able to modify it
only by varying, through the medium of the stomach, the elements out
of which chyle is to be formed and the mode in which they shall be
digested, is a proof that, practically speaking, it is chiefly the laws
or conditions of stomachic digestion which are intended to regulate our
conduct; and that, in obeying them, we in reality obey also those of
intestinal digestion.
* * * * *
The organs concerned in chylification are the _duodenum_, the _liver_,
and the _pancreas_; but in order to avoid repetition, I shall, in
describing the first, notice also the remainder of the intestine.
The _intestine_ or _intestinal canal_, as represented in the
subjoined figure, begins at the pyloric orifice of the stomach P, and
after many windings and turnings, called _convolutions_ (from the
Latin word _convolutus_, rolled or folded together), terminates
in the _rectum_ or _straight gut_ Y, at the external orifice
called the _anus_. Although continuous throughout its whole
extent, the intestinal tube is nevertheless divided by anatomists
into six portions, to each of which a different name is assigned: the
distinction between some of these is more nominal than real, but it
still continues to be made on account of its convenience.
The first grand division is into the small and great intestines; the
former beginning at the stomach, including all the convolutions marked
RSSSS,--and the latter beginning at T, where the small intestine
terminates, and including the large gut UUUUXYY, which surrounds, and
is partly hidden by, the other bowels.
[Illustration]
The small intestines, again, are subdivided into three portions,--the
_duodenum_, the _jejunum_, and the _ileum_; and the larger, in
like manner, into three portions--the _caput cœcum_ or simply the
_cœcum_, the _colon_, and the _rectum_. Of the whole length, the
small intestines constitute by much the greater part, and they differ
somewhat from the larger in function as well as in magnitude.
In _structure_, the intestines exhibit a great analogy with the
stomach. They consist, in common with it, of three coats or
layers of membrane; the _outer_ or _peritoneal_,--the _middle_ or
_muscular_,--and the _internal_, _mucous_, or _villous_.
The _peritoneal_ coat is the white, firm, smooth, shining, and
moist membrane, seen on the outside of the intestine on opening the
cavity of the abdomen. It serves both as a support and as a medium of
attachment to fix the intestine in its place. By its smooth, soft, and
lubricated surface, it admits readily of the change of place among
the bowels necessarily produced by respiration, exercise, and even by
different degrees of distention of the bowels themselves. Every time we
breathe, an undulating motion is communicated to the whole intestines,
which facilitates their action, but which could not take place unless
they were capable of gliding easily and freely over each other. The
peritoneal coat, being strong, extensible, and elastic, is very useful
also as a support to the other coats.
[Illustration]
The peritoneal coat, after forming the outer covering of the intestine,
represented by the dotted line round the circle I in the figure on
next page, is continued from it in the form of a double membrane
(represented by the two dotted lines) towards the spine S, to which
it is first firmly attached by cellular substance; after which the
folds again separate, each being continued or _reflected_, as
it is called, over the whole inner substance of the cavity of the
abdomen in the course shewn by the dotted line, the figure itself
representing a transverse section of the abdomen. By this arrangement
two important objects are attained. _First_, the abdominal
peritoneum AP forms a soft lubricated surface, corresponding to that
of the bowels themselves; and, _secondly_, a firm point of
attachment for the bowels is secured, by which they may be supported
in their proper places, and at the same time admit of some change
of position. The floating portion of the peritoneum M, by which the
attachment is effected, is called the _mesentery_ (from μεσος,
_mesos_, the middle, and εντερον, _enteron_, intestine).
But the intestinal canal being so much longer than the portion of the
spine, to which the mesentery is attached, the latter is necessarily
disposed in folds converging towards the spine, something like the
folds of a fan converging towards its narrow end. In this way, the
mesentery, besides serving as a support to the gut, serves also to
receive and afford protection to the numerous vessels, nerves, and
lacteals which are copiously ramified on every portion, particularly of
the small intestines. This feature, however, will be better understood
by inspecting the wood-cut on page 163, representing a portion of the
bowel II, as attached to the spines by the mesentery MM, along which
the absorbent vessels or lacteals LL are seen to pass from the gut
towards the thoracic duct TD.
The portion of peritoneum by which the small intestines are fixed to
the spine, constitutes what is properly called the _mesentery_.
That portion by which the larger bowel is attached is called the
_mesocolon_, from its enclosing the colon; but in other respects
the membrane presents no difference.
The _muscular_ coat is composed principally of transverse and
longitudinal fibres, and its sole object here, as elsewhere, is to
effect _motion_. By the alternate contraction of the two kinds of
fibres, the contents of the gut are gradually propelled in a downward
direction, just as we see a motion propagated from one end of a worm
to the other; and hence it is sometimes called the _vermicular or
worm-like motion_ (from _vermis_, a worm). Some nauseating
substances, such as emetics, have the power of _inverting_
the order of the muscular contractions, and directing the contents
upwards instead of downwards--whence vomiting ultimately arises. Other
substances, again, have the property of exciting the _natural_
action to a higher degree, and consequently propelling the contents
faster downwards--in other words, of purging. Rhubarb, aloes, and
similar laxatives, especially when combined with tonics, act in
this way, and are consequently best adapted for obviating the kind
of costiveness which arises from imperfect intestinal contraction.
In a natural mode of life, the muscular coat is greatly aided in
its operation by the large abdominal and thoracic muscles, brought
powerfully and frequently into play during active exercise and
employments. When this aid is withdrawn, as it is in sedentary people,
the intestinal action often proves insufficient for the purpose; and
hence the costiveness which is so invariable an attendant on most
females, literary men, and others, whose occupations deprive them of
active muscular exercise in the open air. In females, the use of tight
stays renders the free expansion of the chest and corresponding motion
of the abdomen, altogether impossible, and thus aggravates the evils of
their sedentary mode of life. Hence also the peculiar fitness, in such
cases, of the class of purgatives above alluded to, in preference to
those of a saline nature, which act chiefly by stimulating the mucous
surface to farther secretion.
In addition to the ordinary longitudinal and transverse fibres, the
colon presents three remarkable muscular bands running along its whole
length, and one of which is represented on the colon in the figure on
page 155. On the rectum all the three bands are seen. It is in the
colon and rectum that the feculent matter accumulates before it is
thrown out of the bowels, and these bands are useful chiefly by adding
to their propelling power.
The natural tendency of muscular fibre being to contract it may
naturally be supposed that, after the intestine is emptied, its
opposite sides will come into contact, and, by thus obliterating the
cavity altogether, present an obstacle to the subsequent passage
of any solid matter. But on inspecting the abdomen after death, we
rarely meet with any considerable portion thus contracted; and in
general, the whole intestines are distended to a greater or less
degree, according to circumstances. The agent by which this effect is
brought about, is one known more familiarly by the inconveniences and
pain to which it gives rise when in excess, than by its proper uses,
which are nevertheless important. I allude to the presence of air in
the bowels, which is as necessary to their healthy action as their
muscular contraction itself. Air, in fact, by its expansive energy,
forms the antagonist power to the muscular coat, and serves to dilate
the bowel after the requisite contraction has propelled its contents. A
certain degree of distention, indeed, not only is a stimulus to farther
muscular contraction, but is useful in facilitating the passage of the
subsequent portions of the feculent matter; and hence the injection
of air into the bowels in large quantity, has lately been employed
successfully in overcoming obstinate constipation.
The _mucous_, _internal_, or _villous_ coat of the intestine, also
resembles in many respects that of the stomach. It is a soft velvety
membrane, full of wrinkles or folds through the greater part of its
course, by means of which its surface is greatly increased in extent,
so as to afford ample space for the ramification of the bloodvessels,
nerves, and absorbents, with which it is very plentifully supplied. The
cut on p. 172 will convey some idea of its appearance, as seen in the
smaller intestine. So far as nutrition is concerned, the mucous coat is
the truly _essential_ part of the bowel. It alone is in direct contact
with the chyme, and in its cavity the bile and pancreatic juice perform
their respective parts, and give rise to the formation of chyle,
which is afterwards transmitted from its surface into the general
system. The peritoneal and muscular coats are useful only in affording
protection, and communicating the power of propelling its contents.
The mucous coat appears on examination to be so entirely continuous
with the skin, that no line of demarcation can be detected between
them either at the mouth or at the anus. In structure they greatly
resemble each other, and the sympathy between them is well known
to be very rapid and intimate. Eruptions on the skin, for example,
are almost always owing to disorder of the digestive organs; and
bowel-complaint, on the other hand, is often produced by a sudden chill
on the surface. In like manner, in enormous eaters like those formerly
mentioned, an immense exhalation takes place from both the skin and
the bowels, and in many instances the one supplies the place of the
other in a considerable degree. We have seen, moreover, that in the
lowest tribes of animals, the digesting surfaces and skin are not only
undistinguishable, but actually convertible into each other by the
simple process of turning the animal inside out, when each will perform
the function of the other as well as if it had never done any thing
else.
In common with the skin, too, the mucous coat is charged with the
double function of _excretion_ and _absorption_. For the
former, it is eminently fitted by its plentiful supply of blood, and by
the great number of minute vessels ramified on its surface, from the
extremities of which the excretion takes place. It is by this channel
that much of the waste matter requiring to be removed from the body
is thrown out. Being poured into the cavity of the intestine from the
small arterial branches, it mixes there with the indigestible residuum
of the food and bile, and, united with them, forms the common fæces or
excrement. When the blood is suddenly repelled from the surface by a
chill, and thrown in upon these vessels in large quantity, the natural
excretion is sometimes increased to such an extent as to constitute
bowel-complaint; while at other times, that peculiar form of action
is induced which constitutes inflammation. The local stimulus of
some kinds of food, and of many medical substances, also excites the
secretion to unusual activity. Salts, for instance, have this effect,
and thus often _produce_ numerous fluid evacuations, the substance
or materials of which did not before exist in the bowels; and hence the
mistake into which many fall, of taking more medicine on the ground of
this effect proving that much stuff was lodged in the bowels--when,
in fact, it was not only removed but _created_ by the physic. It
is from exciting a fluid discharge of this description, that saline
purgatives are so useful for lowering the tone of the system when that
is required; but, for the same reason, they are most improper where
relaxation and debility already exist. In Asiatic cholera, almost the
whole fluids of the body are carried off by this channel, leaving the
blood too thick in consistence to circulate longer through the smaller
vessels.
The excretions from the minute arterial branches ramified on the
internal coat are mingled with a bland fluid from the mucous follicles,
the evident use of which is to protect from injury the sensitive
surface of the intestine. Occasionally, however, the mucous secretion
becomes so abundant and viscid, as to adhere with unusual force, and
to impede the formation and absorption of the chyle, and even the
action of the usual purgatives. Worms are then common, and cannot be
expelled except by remedies which tend to remove the mucus in which
they live imbedded.
[Illustration]
To fit the mucous coat for its office of _absorption_, an immense
number of minute vessels, called _absorbents_, are ramified on
its internal surface, the nature and purposes of which are analogous
to those mentioned in the former volume when describing the functions
of the skin.[34] In both structures the absorbents are small capillary
or _hair-sized_ vessels, so infinite in number that at least
one goes to every little point or _papilla_. Those which open
upon the inner surface of the smaller intestines, and which suck in
or absorb the chyle, are called _lacteal absorbents_, or simply
the _lacteals_ or milk-vessels (marked LLLL in the subjoined
wood-cut), from the white colour of the chyle shining through them
and giving them the appearance of vessels full of milk. In that part
of the gut they are so numerous that every minute point of the villous
coat may be seen by the aid of a microscope to contain one with its
mouth open to receive the chyle as fast as it is formed. Even in the
colon the absorbents are numerous; but, as all traces of chyle have
there disappeared, they are much fewer than in the smaller intestines.
In the colon they serve chiefly to remove the more watery portions of
the intestinal contents, by which means the fæces are rendered more
solid and less bulky, and therefore better adapted for being retained
for a time without inconvenience. It sometimes happens that when food
or medicine cannot be swallowed in the usual way, life is preserved by
injecting it into the bowels; in which case the absorbents of the large
gut become active, and carry it into the system. Strong soups, milk,
opium, laxatives, and other remedies are often administered in the same
way, when any reason exists against giving them by the mouth.
There are absorbents in every structure of the body, because
there are everywhere waste particles to be taken up and removed;
but, except in the case of the lacteals, their contents are
_limpid_ or colourless, and hence in other places they are called
_lymphatics_: in almost every other respect, however, the two
classes of vessels are analogous to each other.
The peculiar property by which the minute lacteal vessels imbibe
or take up the white chyle is not well understood. From the fact
in physics that liquids rise in capillary tubes, the inference has
been drawn that absorption in living vessels also takes place from
capillary attraction. But in the animal body the application of the
principle is undoubtedly modified by the properties peculiar to
organization, and one of the most remarkable proofs of this is the
circumstance of the absorbent vessels in different situations having to
some extent a specific adaptation to the qualities of the substances
upon which they are severally destined to act. At one time, indeed,
it was supposed that the principle of exclusive adaptation was so
complete that every absorbent vessel was permanently shut to every
thing except its own peculiar object, and that, from amidst many
elements, each selected its own with unerring tact. But of late it has
been proved that the absorbents are less rigidly discriminating than
was previously supposed, and that substances are readily taken up by
them which Nature never intended them to receive. In mixing madder with
the food of fowls, for example, for the purpose of dyeing their bones,
the colouring matter of the root is taken up without difficulty by the
absorbents along with the chyle, although madder was certainly never
intended to be their natural stimulus. But even admitting this latitude
in its fullest extent, there still exist a fitness and peculiarity of
relation between the absorbents and their _proper_ objects, which
renders the latter more accessible to them than to any foreign body.
The lacteal vessels are most easily seen an hour or two after a meal;
because they are then fully distended with chyle, even in their
smaller branches. The latter, indeed, may then be distinctly traced
proceeding from the different portions of intestine, and gradually
coalescing into larger trunks, as seen at LL in the figure on p. 163.
These, again, terminate in the vessel called the thoracic duct (the
beginning of which is seen at TD in the same figure), by which the
chyle is conveyed almost in a direct course along the spine, and which
is represented at DDDD in the annexed cut. On its arrival at the upper
part of the chest, the thoracic duct crosses over and opens into the
subclavian vein S, just before the latter reaches the right side of the
heart, so that the chyle is there poured into the circulating current
of the _venous_ blood.
[Illustration]
Such is the course of the chyle. But the lacteal absorbents, in their
progress from the intestine to the thoracic duct, pass through the
small glandular bodies called the mesenteric glands (MG, p. 163), where
some change, the nature of which is not at all understood, is produced
upon the chyle, but which seems nevertheless to be of importance to
its constitution. Where these glands are hardened and enlarged, as
they often are in scrofulous children with large prominent bellies and
thin bodies, nutrition is greatly impaired, although the appetite and
stomachic digestion remain comparatively unaffected.
The reason why the chyle is carried so far, to be poured into the
current of the venous blood just before the latter reaches the right
side of the heart, is on consideration not less obvious than cogent.
Chyle itself is not fitted to become a constituent part of the animal
frame. Before it can become so _it must be converted into blood_;
and this can be effected only by exposing it to the action of the air
in the air-cells of the lungs in a state of intimate mixture with the
venous blood. This admixture, again, is insured by the gradual way
in which the chyle advances along the thoracic duct and falls into
the circulating current almost drop by drop; and it takes place just
before the dark blood has finished its course, and is again subjected
to complete _aëration_ in its passage through the lungs. As
explained in the former volume, this aëration is so indispensable
to the renovation of the old and the formation of new blood, that
whenever it is rendered imperfect, either by obstructions in the lungs
themselves or by the absence of a sufficiently pure air without, the
result is invariably injurious to health; because the blood, being no
longer properly constituted, becomes incapable of furnishing a healthy
stimulus and nourishment to all the parts of the body. Hence the rapid
“decline” which follows the appearance of pulmonary consumption, and
other diseases affecting the structure and interrupting the functions
of the lungs.
Every body knows as a fact that bad air is hurtful, and that wasting
disease of the lungs is attended with rapid loss of flesh and strength;
but the manner in which these effects are produced is not so familiarly
known. Yet, in a practical point of view, a knowledge of the principle
is highly important. Properly considered, _respiration is in reality
the completion of digestion_. The stomach may convert the food
into chyme, the small intestines may convert the chyme into chyle,
and the absorbents may take up the latter and duly convey it into the
circulating system; but unless it undergo the necessary change in the
air-cells of the lungs it will not constitute good blood or afford
due nourishment to the body. Hence it is that those among the working
classes who are much confined in an impure and insalubrious atmosphere,
even when plentifully supplied with food, are generally thin and
ill-nourished; and hence those who, along with good digestion, have
small narrow chests and very limited respiration, are commonly found to
be constitutionally lean,--while those who, along with good digestion,
have amply developed lungs and free and powerful respiration, are at
the same time remarkable for proportional vigour of nutrition and
stoutness of body. It is on this account that in chronic pulmonary
disease recovery is always to be distrusted, unless, along with the
disappearance of the prominent symptoms, restoration of the lost flesh
occurs. If nutrition remains impaired, however great the relief may be
in other respects, there is reason to believe that the lungs are still
so extensively diseased as to injure their functions, and that, on the
application of any fresh exciting cause, the dormant mischief will
resume its activity. In such cases, when stomachic digestion is sound,
a full diet generally over-stimulates the system, by pouring into the
blood more chyle than the lungs are able to assimilate; in consequence
of which it is diffused over the whole body in an imperfect state of
preparation.
The mucous membrane is, like the skin, well provided with
_nerves_, and has a mode of sensation peculiar to itself. Every
villous point indeed has a nervous fibre ramified on it, to give it
the necessary sensibility to its own stimuli. It is true we are not
conscious in health of the impressions made on the intestinal nerves;
but this, as already shewn in describing the stomach, is a privilege
and not a defect. They recognise their appropriate stimuli, and cause
the necessary actions to follow without requiring aid from the will.
But when they meet with substances which ought not to be there, such
as pieces of undigested food, or foreign bodies which have no natural
relation to their constitution, they immediately indicate uneasiness,
and excite the muscular contractions to rid them of the offending cause.
To secure full and natural action in the intestinal canal, several
principal conditions are thus necessary, failure of any of which may
impair their activity. The first condition is well-digested chyme and
chyle; the second, a due quantity and quality of mucous and vascular
secretions from the villous coat; the third, full contractile power in
the muscular fibres of the intestine, and free action of the abdominal
and respiratory muscles; and the last a due nervous sensibility to
receive impressions and communicate the necessary stimulus. And hence,
when the bowels act imperfectly, it is of importance to ascertain
to what cause the inability is to be ascribed, that an appropriate
treatment may be devised.
* * * * *
Such are the general structure and uses of the intestinal canal; but
there are modifications in its individual portions on which it may
be right to offer a few additional remarks. We shall begin with the
_duodenum_.
The _duodenum_ (from _duodeni_, twelve, being considered
equal in length to twelve finger-breadths) commences at the pyloric
orifice of the stomach, from which it crosses over under the lower
surface of the liver, towards the right side; it then descends in
front of the right kidney, and there forming a second curve, it
proceeds again towards the left, and a little beyond the spinal
column terminates in the jejunum. It thus describes a course like the
letter C, and has its convexity turned towards the right, while the
_pancreas_ or sweetbread (PP) lies in the space enclosed by its
concavity. To enable the reader to form some notion of the relative
position of these parts, I have introduced a wood-cut on the next page,
shewing the situations and appearance of the different organs after the
intestines, as in the figure on page 155, have been removed from the
body. The letters LLLL point out the inferior surface of the liver,
a little raised from its natural position to shew the gall-bladder
G and the pancreas PP, round the right end of which the duodenum is
curved. S indicates the spleen, with a vacant space over it, in which
the stomach lies. The kidneys, KK, lie one on each side of the spine;
and the two pipes UU are the ureters which convey their secreted
fluid to the bladder B. The letters AA indicate the great artery (the
_aorta_), through which the nutritive blood descends to supply the
bowels and lower parts of the body; and VV mark the corresponding vein
(the _cava_), by which the dark blood returns from the extremities
towards the heart. R is the beginning of the _rectum_ or straight
gut seen at YY in the cut on page 155.
[Illustration]
The duodenum, being thus in the immediate vicinity of the spine, is
fixed firmly down in its position by the connecting membrane, and is
not left to float loosely in the cavity of the _abdomen_ or belly.
Had it not been tied down in this way, it would not only have acted
by its weight as a continual drag upon the stomach and disturbed its
functions, but likewise have been constantly altering its own relation
to the pancreatic and hepatic (or liver) ducts, and thereby affecting
the flow of their respective fluids into its cavity, by which the
chylification would have often been interrupted.
[Illustration]
The duodenum is much smaller in diameter than the stomach, but larger
than the _jejunum_ or _ileum_; and its muscular coat is also thicker.
From its size and the importance of the changes effected in it, it
has been considered by some as a secondary stomach or _ventriculus
succenturiatus_. Its mucous coat, which has a soft velvety feel,
presents a greater multitude of the folds or plaits already described,
and which have for their object to extend its surface and delay the
passage of the chyme. Some notion of their appearance may be formed
from the subjoined wood-cut. These folds or _rugæ_ are called
_valvulæ conniventes_ or _folding valves_, and are inherent in the
nature of the mucous coat, and not produced by mere folds of the
whole thickness of the intestine, consequently they exist even when
the latter is distended. They are comparatively few in number in the
part of the duodenum near the stomach, and gradually multiply in the
course downwards till they arrive at the maximum of development at its
lower end and in the jejunum: they again diminish in the ileum, and
disappear altogether in the large gut. The bloodvessels and nerves of
the duodenum are extremely numerous, and indicate the importance of its
functions.
The duodenum serves to receive the chyme as it issues from the stomach,
and to prepare it for the farther changes which it is about to undergo.
But as other organs, namely the _liver_ and _pancreas_, are
directly concerned along with the duodenum in effecting chylification,
it will be proper to take a cursory view of them also before describing
the rest of the intestine.
The liver (LLLL, p. 171) is a very large glandular body lying under
the short ribs of the right side, immediately below the diaphragm or
midriff, to which it is attached by strong ligamentary bands, which
sustain its weight and keep it in its place. Its office is to secrete
the bile, but it differs in one important particular from every other
secreting organ. Its secretion is derived, not, as in other instances,
from the arterial or nutritive blood, but from the _venous_ or
exhausted blood, which is collected from all the abdominal organs, and
transmitted through it for this purpose on its way back to the heart.
From this peculiarity, it is legitimately enough inferred that the
liver serves the double purpose of providing a fluid indispensable
for chylification and the proper action of the bowels as organs of
excretion, and also of separating from the venous blood useless or
spent materials, which require to be thrown out of the system. The
influence of the bile as a stimulant to the bowels is proved by the
fact that costiveness ensues when it is deficient in quantity, and an
opposite condition when the secretion is redundant, as during the heat
of autumn.
_Bile_ is a bitter, viscid, greenish-yellow fluid, the taste
and general appearance of which are familiar to most people, and the
office of which in the animal economy must be one of no small moment,
if it be justly chargeable with even a tenth part of the catalogue of
human ills which are laid to its account. Its secretion seems to go on
continuously; but the quantity produced depends much on the amount of
venous blood which is circulating through the liver at the time. Hence,
in health, it is always greatest soon after a meal; because, as we have
already seen, the supply of blood in both the arteries and the veins
connected with digestion is then at its maximum.
But as the secretion of the bile is constantly going on, and its
presence in the duodenum is required only when the latter contains
chyme, a contrivance becomes requisite for storing it up in the
interval, to be ready for use when wanted. This is effected by the
small shut sac or bag G, named the _gall_ (or bile) _bladder_, which
adheres to the lower surface of the liver, and is always most full
after a fast of some duration. The bile contained in the gall-bladder
is generally more viscid, dark, and bitter, than that which proceeds
directly from the liver--apparently from the absorption of its more
fluid parts. It is in this bag that _gall-stones_, as they are called,
are sometimes formed, and it is their passage through the narrow tube
in which it terminates that causes the acute pain so often complained
of in that affliction.
From the liver the bile is conducted into the duodenum through a
membranous tube, of about the diameter of a quill, and which is
called the _biliary_ or _hepatic duct_. In its course a similar pipe,
called the _cystic duct_ (from κυστις, _kystis_, a bladder), from the
gall-bladder, unites with it into one trunk, like the two limbs of the
letter Y; and this trunk enters the duodenum by an orifice common to it
and the pancreatic duct.
In the healthy state bile is to be found only in the duodenum, and
not in the stomach; although one would suppose the contrary from the
familiar way in which we speak of the stomach being oppressed with
bile, and of our being “very bilious.” When vomiting is excited,
either artificially or by illness, we, no doubt, often bring up
plenty of bile. Sometimes this bile has been existing in the stomach,
and causing nausea; but very often it is brought into the stomach
solely by the inverted action which constitutes vomiting, and was
consequently placed there by the very remedy which is supposed to
have cleared it away. The process of vomiting is accompanied by an
inverted action of the intestinal canal whereby it propels its contents
upwards instead of downwards, and thus the bile is, as it were, forced
up from the duodenum into the stomach, instead of being propelled
downwards and expelled in the usual way. Hence, in sea-sickness for
example, the first fits of retching generally bring up nothing but
food or mucus--the real contents of the stomach,--and it is only after
continued straining that bitter bile makes its appearance. In the
healthy state, fat or oily food often causes the presence of bile in
the stomach, as if its aid were necessary there for the accomplishment
of digestion.
The _pancreas_, or sweetbread, PP, is a large oblong gland, which
lies across the spine, and secretes a fluid almost identical with the
saliva. Its duct, as stated above, enters the duodenum along with the
biliary duct, so that the two fluids meet at their entrance, which
takes place at the first curvature of the intestine, at the distance of
about one-third of its whole length from the stomach.
The bile and pancreatic juice thus poured out together are both
requisite for the formation of chyle, and apparently modify the
action of each other. The bile being somewhat of an unctuous nature,
and the pancreatic juice somewhat alkaline, their union forms a kind
of saponaceous compound, which is less irritating and more easily
incorporated with the chyme than pure bile.
In proportion as the chyme is formed and expelled from the stomach,
it is received into the duodenum, where it probably undergoes some
farther change even before arriving at the entrance of the biliary and
pancreatic ducts. From the numerous folds or wrinkles which line the
inner surface of the duodenum and impede the motion of its contents,
and also from the intestine itself being more fixed down, and less
subjected to the influence of the movements of respiration, the
progress of the chyme along its surface is very slow. Every particle of
chyme is thus allowed to receive its share of the bile and pancreatic
juice as it proceeds on its course, and time is afforded for the
requisite changes taking place.
By simply stating that, in the duodenum, the chyme becomes mixed with
the two fluids just mentioned, and that the result is its separation
into a fluid, milky, and nutritive portion, named _chyle_, which
is absorbed by the lacteals, and a darker yellow-coloured thickish mass
which remains in the bowel, we communicate to the reader almost every
thing that is known on the subject. Theories and conjectures could be
added, but scarcely any facts of a very positive nature.
* * * * *
The remainder of the small intestine, namely, the _jejunum_ (from
_jejunus_, fasting or hungry, because it is generally empty) and
the _ileum_ (from ειλεω, _eilio_, I twist or turn about),
marked RSSSS in the cut on p. 155, are merely continuations of the
duodenum, and have precisely the same number of coats and the same
general structure. Their inner surface presents the same kind of
folds or _rugæ_, whereby the extent of the mucous membrane is
increased, and ample space given for the ramifications of bloodvessels
and the origin of the absorbents by which the chyle is sucked up and
carried into the system. _Exhalation_ or _exudation_ also
goes on from their surface, and, in bowel-complaints, often becomes so
excessive as in a few days to reduce the patient to the extremity of
emaciation and weakness.
As the contents of the jejunum and ileum advance, the proportion of
chyle in them becomes smaller and smaller, and the residual matter
becomes more and more consistent, yellow, and fetid--approaching, in
short, to the ordinary appearance of excrement when expelled from
the body. In accordance with these changes, the number of absorbent
vessels, and the distinctness of the villous folds, gradually diminish
as we proceed downwards, till, on arriving at the termination of the
ileum in the colon or great gut, they altogether disappear, and the
contents assume the colour, smell, and appearance, by which excrement
or feculent matter is characterized.
The division between the small and great intestines is indicated, not
only by marked differences in their diameter and external appearance,
but also by an internal valve placed between them, the object of which
is to prevent the contents of the colon from following a retrograde
course and returning to the ileum. It is also worthy of notice, that
the colon is not a gradually enlarged continuation of the ileum. On
the contrary, the latter enters the side of the colon almost at right
angles to its course, at a little distance from its commencement. The
small portion of the colon which thus lies at one side of the entrance
of the ileum, and which has of course no opening at its extremity, is
thence called the _caput cœcum coli_, or _blind head_ of the
colon, or simply the _cœcum_. Its position is at T in the figure
on p. 155, but it is hidden by the folds of the ileum.
The _colon_ (from χοιλον, _coilon_, hollow) or great gut UUU
in the same figure, constitutes not more than one-fifth in length of
the intestinal canal. It begins at the lower part of the right side of
the belly, at T in the cut on page 155; rises upwards on the same side
towards the liver; crosses over to the left side in contact with the
stomach; descends along the left side of the abdomen; makes a turn at
UWX like an italic _s_, (and hence called _sigmoid_ flexure),
while lying on the left haunch-bone; and lastly, terminates in the
_rectum_ or _straight gut_ YY at the _anus_. Being fixed
by local attachments, the colon remains always in the same situation,
and thus describes a figure not unlike a square, in the centre of which
lie the whole of the smaller intestines. In the cut referred to, the
left portion is hidden behind them.
The diameter of the colon is about double that of the small intestines.
In structure it is analogous to them, having three coats; but the
_valvulæ conniventes_ or folds of the mucous coat, are no longer
to be seen, and with them all traces of chyle and chyle-bearing vessels
also disappear. The colon serves more as a reservoir for waste or
excrementitious matter than as a vital organ. Absorption is carried on
from its inner surface, but through the medium of lymphatic absorbents
and minute venous ramifications, and not of lacteals. Hence not only
food, but medicine, are frequently administered by being injected into
the rectum, and life has been saved in this way when nothing could be
given by the mouth.
The passage of the intestinal contents from the stomach downwards, is
affected chiefly by the _peristaltic_ or _vermicular_ motion,
that is, the successive muscular contraction of the middle or fleshy
coat, already frequently adverted to; and this, in its turn, is greatly
aided by the constant but gentle agitation which the whole digestive
apparatus receives during the act of breathing, and during exercise
of every description. In inhaling air into the lungs, the diaphragm
is depressed, the bowels are pushed down, the walls of the belly
yield, and it becomes protuberant. When air is thrown out from the
lungs, the diaphragm rises into the chest, the bowels follow, and the
belly becomes flattened and drawn in. The stomach and bowels are thus
placed between, and receive a never-ending impulse from, two bodies
differently placed and in continual motion. During exercise, breathing
is deeper, and muscular contraction greater in power and in extent;
and hence the assistance afforded is also increased. Those who take
no exercise, or who have the chest and bowels confined and bound down
by tight stays and bandages, lose this natural stimulus, and have, in
consequence, the bowels obstinate and troublesome.
The great extent and capacity of the intestinal canal in herbivorous
animals, and others living on bulky and innutritious food, have been
already noticed, and their reason explained. Perhaps it ought to be
added, that an additional reason is the fact, that the digestion of
vegetable nutriment is not, like that of animal food, completed in the
stomach, but in the intestines. It is familiarly known, for example,
that when digestion is weak, fruits and fresh vegetable aliments often
pass through the bowels very little changed; and that, even at the
best, they are digested more slowly than animal food. On examining the
bodies of animals at different intervals from the time of feeding,
the distinguishing fibrous structure of vegetable food is observed
to diminish in proportion to its distance from the stomach, and it
does not finally disappear till it is nearly arrived at the end of
its course. From this it has been inferred, that the digestion of
vegetable matter is only partially accomplished in the stomach, and
that it requires the aid of the intestinal juices for its completion.
Delabere Blaine arrives at the same conclusion, from considering the
peculiar digestion of the horse. In the horse, the stomach is a simple
bag, of very moderate size, and yet that animal not only can drink a
gallon or two of water at a time, but can eat a much larger quantity of
hay or grass than its stomach seems to be capable of containing. Blaine
explains this, by stating that, in reality, oats and hay are not long
retained in the stomach, and that after receiving the requisite supply
of gastric juice, and undergoing its influence to some extent, they
are gradually propelled towards the duodenum, where their digestion
is continued, but not completed till long after being subjected to
the action of the bile and pancreatic juice, and passing through
the remainder of the small intestine. It is owing, he adds, to this
speedy evacuation of the stomach, that the horse is less inclined to
drowsiness, and less incommoded by active exercise, soon after meals,
than almost any other animal.
The late Baron Dupuytren had several opportunities of observing
something analogous to this in the human subject. He had, at various
times, under his care, patients in whom an opening into the intestine
had taken place at different distances from the stomach, and through
which the intestinal contents readily escaped. On giving several kinds
of food at one meal, he remarked that they presented themselves at
the wound in the _inverse_ order of their digestibility. Thus,
fresh vegetables always made their appearance first, still retaining
much of their peculiar structure; while animal substances either did
not appear at all, or were so much altered in appearance as scarcely
to be recognised. In the natural evacuations, however, the vegetable
structure was generally imperceptible; so that a considerable change
must have taken place on it as it advanced through the bowels, after
passing the seat of the wound. Londe had occasion to remark the same
thing in a lady in whom an opening into the intestine existed. When
she ate cutlets or chicken, digestion was so far advanced before they
reached the opening that their identity could not be recognised. But
when she ate spinage, carrots, or vegetable soups, these articles
arrived at the orifice scarcely at all changed. In this patient also,
vegetable substances passed rapidly out of the stomach. Thus salads,
prunes, apples, and spinage made their appearance at the opening in
about an hour; while the remains of animal food never appeared in less
than three hours. Londe indeed lays it down as a principle, that where
the wants of the system are not great, the digestion or alteration of
innutritious substances, such as stewed or raw fruits, carrots, &c.,
“begins only in the ileum.” He adds, that he “has always seen these
substances resist the action of the acid and mucous juices of the
stomach, as well as that of the pancreatic and biliary secretions.”[35]
From the circumstance of vegetable aliment containing _little
nourishment_ and _much indigestible matter_, it naturally
happens that a larger quantity of refuse remains to be thrown out of
the bowels when it constitutes the chief part of the diet, than when
animal or farinaceous food, which contains _much nourishment_ and
_little indigestible matter_, is used. Hence, as a general rule,
the bowels act more freely, or are more open, in the former than in the
latter case; and hence the common saying, that milk, eggs, jellies,
and meat, are _binding_. They have the appearance of being so
chiefly because they are almost wholly absorbed. But as neither the
stomach nor the bowels are adapted in structure for very concentrated
food, such articles cannot be long used with advantage. Brown and rye
bread, and fruits, are in repute for relieving a costive habit of body,
and their usefulness is explicable on the same principle. They leave a
large residue to be thrown out of the system, and this residue forms
the natural stimulus of the bowels, and consequently excites them to
freer action. This effect is probably aided also by the stimulus which
the indigestible refuse imparts to the mucous glands, increasing the
lubricating secretion, and giving additional facility to the propelling
powers.
In the preceding exposition of the structure and functions of the
organs of digestion, many omissions necessarily occur, and many
questions of much intrinsic interest are passed over with very little
notice. But a minuter survey was incompatible with both the objects
and the limits of the work. My great aim was, not so much to extend
the bounds of physiology, but to turn to a useful purpose what is
already known in regard to one of its most important departments, and
to interest a larger class of people in its cultivation. If I have
said enough to make the points of doctrine on which I have touched
intelligible to the ordinary reader, and to impress him with a just
sense of their practical value, I shall have accomplished the utmost I
have sought to attain.
PART II.
THE PRINCIPLES OF DIETETICS VIEWED IN
RELATION TO THE LAWS OF DIGESTION.
CHAPTER I.
TIMES OF EATING.
The selection of food only one element in sound digestion--Other
conditions essential--Times of eating--No stated hours for
eating--Five or six hours of interval between meals generally
sufficient--But must vary according to circumstances--Habit
has much influence--Proper time for breakfast depends
on constitution, health, and mode of life--Interval
required between breakfast and dinner--best time for
dinner--circumstances in which lunch is proper--late dinners
considered--their propriety dependent on mode of life--Tea and
coffee as a third meal--useful in certain circumstances.--Supper
considered.--General rule as to meals.--Nature admits of
variety,--illustrations--but requires the observance of
principle in our rules.
Having in the first part of the present work traced the progress of
the food through its successive stages of preparation for becoming a
constituent element of the animal frame, and examined the structure
and nature of the various organs engaged in digestion, I shall now
endeavour to turn the exposition to account, by making it as far as
possible subservient to a closer and more rational observance of the
laws of digestion, and to a better adaptation of diet and regimen to
different ages, sexes, and constitutions, than that which is generally
prevalent. I am deeply sensible of the imperfections which will abound
in this part of the work; but, at the same time, I am so strongly
impressed with the urgent importance of the subject, and with the
success which will infallibly attend its further investigation on sound
physiological principles, that I consider the likelihood of personal
failure to be of very secondary importance, when compared with the
benefits which will accrue to society from the exertions of others
whose labours may be more profitably directed by an acquaintance with
the guiding principles unfolded in these pages.
According to the popular notion of dietetics, the selection of the
proper kind of food seems to constitute the _only_ condition
required for the enjoyment of healthy digestion. Hence medical men are
constantly questioned whether this or that article of diet is good or
bad for the stomach, while curiosity rarely if ever extends so far as
to inquire whether Nature has annexed any other conditions which also
it may be expedient to know and to observe. In reality, however, the
choice of aliment is but one out of many circumstances which require
to be attended to; and it often happens that the same food which is
digested with ease when the collateral conditions are fulfilled, will
remain for hours on the stomach unaltered when they are neglected. Some
of these conditions, therefore, I shall now endeavour to point out. And
first, of
* * * * *
TIMES OF EATING.--If we look to the exposition of the objects
of eating already given in treating of appetite, it will be obvious
that Nature intended us to regulate our meals by the demands of the
system, and not to eat at stated hours as a matter of course, whether
nourishment were required or not. If we are engaged in occupations
which induce a rapid expenditure of material, or if growth is going
on so fast as to require unusually ample supplies, food ought to be
taken both more frequently and in larger quantity than when we are
differently circumstanced; or, in other words, _food ought to bear a
relation to the mode of life and circumstances of the individual_,
and not be determined by a reference to time alone.
In reality, however, the animal economy is constituted with so strong
a tendency to periodical activity, that as great an approximation as
possible ought to be made to fixed times of eating. In general little
difficulty and much advantage attend the arrangement; because where the
mode of life is regular and nearly the same throughout a whole class,
the same waste will go on, and consequently the demand for a supply of
nourishment in all the individuals composing it will be felt at nearly
the same intervals, subject only to such variations as are induced by
original differences of age and constitution. As regards each class,
therefore, regularity in the recurrence of their meals is not less
natural than advantageous; and it is only when we attempt to combine a
given order of diet with different and even incompatible modes of life
that Nature refuses to sanction the arrangement.
So strong indeed is the tendency to periodicity in the system, that
appetite returns for a time at the accustomed hour, even after the mode
of life, and consequently the wants of the system, have undergone a
change; and if not gratified it again subsides. Ultimately, however,
it calls with too strong a voice to allow of its being thus disregarded.
Nature has accorded to man considerable latitude in fixing the
interval within which the demands of appetite must be gratified, and
in this provision has obviously had in view the infinite variety
of circumstances in which he may be placed in the discharge of his
numerous duties. As a general rule, five or six hours should elapse
between one meal and another--longer if the mode of life be indolent,
shorter if very active. Digestion occupies from three to five hours,
according to the nature of the meal and circumstances of the case,
and _the stomach requires an interval of rest after the process
is finished, to enable it to recover its tone, before it can again
enter upon the vigorous performance of its function_. Appetite,
accordingly, does not begin to shew itself till some time after the
stomach has been empty, and if food be taken before it has recovered
its tone, the secretion of gastric juice and the contraction of its
muscular fibres are alike imperfect, and digestion consequently
becomes impaired. If, again, food be taken before the digestion of the
preceding meal be completed, the result will be still worse; because
the whole of the gastric juice which the stomach can secrete being
already engaged in the solution of the first meal, the one subsequently
taken necessarily remains unsupplied, and consequently liable to
undergo the same chemical change--fermentation--which would occur in
it if exposed _out of_ the _stomach_ to an equal degree of
heat and moisture. And, therefore, Dr Kitchener, in alluding to the
advantages arising from giving the stomach an occasional rest, truly
and forcibly remarks, that “unless the constitution is so confoundedly
debilitated that the circulation will not run alone, abstinence is
the easiest--cheapest--and best cure for the disorders which arise
from indigestion or intemperance.” (P. 160.) In these cases, indeed,
abstinence is to the exhausted stomach what repose is to the wearied
muscles, and hence the benefits resulting from it.
The interval between each meal ought to be longer or shorter in
proportion to the quantity eaten, and to the more or less active habits
of the individual; and it would be absurd to fix the same standard for
all. A strong labouring man, whose system is subjected to great waste
from being engaged all day in hard work, will require not only more
frequent but more copious meals than an indolent and sedentary man; and
those who eat very little will require to eat at shorter intervals than
those whose meals are heavy. An invalid on restricted diet may thus
require to eat every four hours, where formerly, with a more copious
diet, once in six hours was sufficient. Some indeed are so constituted
as to require only one or two abundant meals in twenty-four hours.
Early training exercises great power over the stomach as well as over
the mind. In savage life, where the supplies of food are precarious,
a single meal may be copious enough to serve for two or three days
together. The monks of La Trappe make it part of their religion to
eat only once a-day, and nothing but vegetable food--unless when
sick, in which case milk is allowed; but it is long before they
become reconciled to the restriction. I once travelled for three days
in a French diligence with one of the order, then on his way from
Italy to the Monastery of La Trappe, near Nantes, and observed that
he scrupulously adhered to his single meal. He had a dispensation,
however, authorizing him to eat animal food and use wine during his
journey; and I was surprised at the extent to which he availed himself
of the permission, by devouring at one time a store sufficient to last
for a week instead of a day. But, as in the case of the Boa constrictor
in similar circumstances, a deep lethargy immediately succeeded, and it
was not till four or five hours afterwards that his almost apoplectic
features became again animated and expressive: long before next meal,
however, his renewed appetite betrayed itself by expressive glances
towards the comforts of the breakfast-table.
Nature, then, _has fixed no particular hours for eating_, but has
left us to adapt our regimen to our respective ages, constitutions, and
modes of life. Where the mode of life is uniform, fixed hours may be
adopted; where it is irregular, we ought to be guided by the real wants
of the system as indicated by appetite.
According to this principle, meals ought to be early or late in
proportion to the habits of the individual. If, adhering to the order
of Nature, we work by day and sleep by night, then early breakfast,
early dinner, and an early evening meal, will undoubtedly be the most
conducive to sound digestion and the enjoyment of health. But if,
against the laws of Nature, we rise from bed late in the forenoon,
reserve our activity till late in the afternoon, and do not go to sleep
till two or three hours before day-break, then assuredly the late
breakfasts and dinners of the fashionable society of the present day
are the best for our comfort that can be devised; and the chief error
lies in the practice of those who, while they in other respects live in
conformity with nature, adopt the hours which are suitable for those
only who turn night into day and day into night.
The proper time for taking breakfast depends a good deal on the
individual constitution and mode of life. Those who eat supper ought
not to breakfast till one or two hours at least after rising; but
persons who dine late and eat nothing afterwards require breakfast
sooner. Individuals of a delicate frame are often unable for either
bodily or mental exertion in the morning, and are invariably injured
by any attempt at exercise or serious thinking before breakfast; but
strong healthy persons and those in whom digestion is naturally slow,
may enjoy and even be benefited by two or three hours of activity
before their morning meal, especially if accustomed to eat supper.
Experience is the only sure guide in such cases, but, as a general
rule, breakfast about half an hour or an hour after rising will be
found most beneficial; and those who rise very early will do well to
follow the French custom of taking a cup of coffee or tea, and bread,
on getting up, and reserve their appetite for a more substantial
breakfast three hours later. This is an invaluable rule for students,
who often seriously impair their digestive functions by studying for
hours in the morning, regardless of the craving of the system for
nourishment and support.
If exposure of any kind is to be incurred in the morning, whether to
the weather or to the causes of disease, it becomes a matter of much
importance that breakfast or some substitute for it, should be taken
previously. It is well known that the system is more susceptible of
infection, and of the influence of cold, miasma, and other morbid
causes, in the morning before eating than at any other time; and hence
it has become a point of duty with all naval and military commanders,
especially in bad climates, always to give their men breakfast before
exposing them to morning dews or other noxious influences. Sir George
Ballingall even mentions a regiment quartered in Newcastle, in which
typhus fever was very prevalent, and in which, of all the means used to
check its progress, nothing proved so successful as an early breakfast
of warm coffee. In aguish countries, also, experience has shewn that
the proportion of sick among those who are exposed to the open air
before getting any thing to eat is infinitely greater than among those
who have been fortified by a comfortable breakfast. Where there is any
delicacy of constitution, the risk is of course increased.
The cause of this susceptibility in the morning is not difficult to be
discovered. Not only have the stomach, duodenum, and upper intestine,
been entirely empty for several hours, but the absorbents and other
parts engaged in the function of alimentation have likewise been in
a state of repose, and now awake, refreshed, and ready for action. A
considerable exhalation from the skin and lungs has, at the same time,
been going on; which, taken along with the deposition of new particles
to the existing organization, necessarily reduces the quantity and
quality of the circulating fluids, and thereby communicates a stimulus
to the absorbents which fits them for imbibing that nourishment, of
which the system stands peculiarly in need, but which, where legitimate
food is denied to them, equally excites them to imbibe any morbid
agent which may happen to solicit their action. The great loss of fluid
by exhalation during the night, and the consequent demand for liquids
in the morning, explain why our first daily meal is almost universally
of a more fluid and less substantial description than any of the
subsequent ones; while our active exertion and loss of solids during
the day create a proportionate demand for a more substantial repast in
the afternoon.
The function of absorption then is at its highest pitch of activity in
the morning, simply because every part of the frame is craving for a
supply to repair the losses which it has sustained; and if the body be
exposed to miasma or other impurities, they will be much more easily
and speedily absorbed by the skin, the pulmonary membrane, and the
stomach, before eating than after the absorbents have been supplied
with their legitimate food. This is the true theory of the greater
susceptibility of infection and other poisonous influences when the
stomach is empty.
So rapid is absorption from the stomach in the morning, that I have
repeatedly seen _nine_ tumblers of a saline mineral water taken
at eight o’clock, and a very hearty breakfast finished within half an
hour after the water was drunk! When in bad health three years ago,
I observed almost equal expedition in my own person. I took half a
pint of ass’s milk at seven o’clock, and in consequence of coughing
violently was frequently seized with vomiting and retching within
twenty minutes after taking it; but only twice or thrice was any
portion of the milk perceptible, although the stomach was entirely
emptied. This was even more remarkable than the other case, inasmuch
as milk undergoes digestion, which water does not. In allusion to this
rapidity of absorption, Sir Francis Head, in speaking of the quantity
of the chalybeate waters swallowed of a morning at the Brunnens of
Nassau, humorously remarks, that “one would think that this deluge of
cold water would leave little room for tea and sugar; but, miraculous
as it may sound, _by the time I got to my ‘Hof’ there was as much
stowage in the vessel as when she sailed_: besides this, the steel
created an appetite which was very difficult to govern.”[36]
In setting out early to travel, a light breakfast before starting is a
great protection against colds and subsequent fatigue or exhaustion. I
am quite aware that robust and healthy men can and do take much active
exercise before breakfast, with apparent impunity if not benefit, and
I have often done so myself; but experience ultimately taught me that
I became sooner exhausted on continuing the exertion through the day,
than when I _began_ by eating a little. During the first winter
of my studies in Paris, I regularly attended the surgical visits at
the Hotel Dieu, which began at six o’clock in the morning and lasted
till nine or frequently half-past nine. Not being then aware of the
principle under discussion, I ate nothing till my return home; but I
felt more weariness before the day was done than the mere exertion
ought to have produced. At last, on noticing for a time the regularity
with which many of the work-people passing along paid their respects
at a small shop, the only one then open, where fancy rolls were sold,
along with wine and brandy, I thought of following their example,
and trying how far a roll would add to my comfort. I soon found great
reason to be pleased with the expedient, and discovered that I was not
only less exhausted during the day, but more able to follow the lecture
which concluded the visit, and in possession of a keener appetite for
breakfast at my return; and ever since, I have acted on the principle
now inculcated, and with marked benefit. I was then astonished at the
regularity with which the Parisian workmen seemed to take their morning
allowance of brandy on their way to their labours, apparently for the
very purpose of getting that wholesome energy which they ought to have
sought in food alone.
During the prevalence of cholera both here and on the Continent, it was
often remarked that a large proportion of the attacks occurred early in
the morning, in persons who had gone to bed apparently well. Chronic
invalids and persons of a delicate habit of body are also familiar with
the fact of the animal heat and general vigour diminishing towards
morning. When reduced in strength by pulmonary complaints, I often
passed the night in comparative comfort, sure to awake about four or
five o’clock with a feeling of chill and absence of animal heat, which
I could not dissipate till after receiving sustenance.
From these facts, the general inference is clearly warranted, that
delicate persons ought to have some kind of food soon after rising,
and that even those who are robust will act wisely in not exposing
themselves unnecessarily to fatigue, infection, or other morbid causes,
without having previously supplied the wants of the system, either
partially by a cup of coffee, tea, or milk, or entirely by a regular
breakfast. Where fever, for example, is in a family, the danger of
infection will be much greater to a person going directly from his own
bed to the bed-side of the patient, than to one who first takes the
precaution of drinking were it only a cup of coffee. I have elsewhere
noticed the safety which Captain Murray obtained for his crew in the
West Indies, partly by attention to this rule; and have likewise
referred to the experience of Sir George Ballingall even in our own
climate.[37]
In boarding-schools for the young and growing, who require plenty of
sustenance and are often obliged to rise early, an early breakfast
is almost an indispensable condition of health. On the Continent, in
similar establishments, seven o’clock is the common hour for breakfast,
especially in summer.
In recommending what I conceive ought to be the general rule, let me
not be understood as wishing to extend it so far as to advise those
whose constitutions admit of two or three hours’ activity before
breakfast, to abandon what experience proves to be beneficial to them.
My only wish is to help those who are in doubt as to choosing the plan
which is most likely to be of advantage, and to relieve those who are
already suffering from ignorance.
* * * * *
The morning meal being comparatively a light one, and the stomach
being then in high vigour, digestion goes on briskly, so that appetite
revives within a shorter time than after the more substantial dinner.
Accordingly, in all nations and classes of society not perverted from
the course of nature, a longer interval than five hours rarely elapses
between breakfast and dinner. Our forefathers dined at noon, as our
sailors continue to do at the present day. Over no small portion of the
Continent of Europe, the same primitive hour is still adhered to; and
among the labouring population of Great Britain, one or two o’clock is
the common dinner hour, eight or nine being that of breakfast. Even the
rich manufacturers of Manchester, and other English towns, continue to
this day to dine at one o’clock; and the very universality of a mid-day
meal among those who rise early, is itself a strong presumption in
favour of its propriety, and of its being in harmony with the laws of
the animal economy.
To prevent business from interfering unduly with digestion, it was
formerly the custom in Edinburgh to shut up shops and counting-houses
for two hours in the middle of the day; and in Switzerland, I have
seen the same practice followed. The members of the family being then
assembled, relaxation and enjoyment take the place of the cares of the
world; and the result is highly satisfactory. The appetite is keen
enough to induce them to eat with zest all that nature requires, while
it wants the resistless force which is given by a fast of eight or nine
hours. There is consequently slower mastication, less cramming, and a
much earlier return of the aptitude for business; while at the same
time the mental and bodily faculties are refreshed by the interruption
of their accustomed labour, and the affections cherished by healthful
domestic intercourse taking place before too much weariness is induced
to permit of its being enjoyed. In England, such weariness is a very
common occurrence. The parent and husband, exhausted by the eager
pursuit of wealth during the livelong day, returns home in the evening
jaded and harassed, and little able to take pleasure or interest in
the enjoyments of his wife and family. Hence, indeed, too often arise
indifference and unhappiness between those whom Nature has formed, as
if on purpose to suit each other.
In enterprising commercial communities--in London and Liverpool for
example--it is a common practice to hasten away to the counting-room
immediately after an early breakfast; to remain there in active
employment from nine or ten o’clock in the morning till six o’clock
in the evening, and then to hurry home to a late dinner at six or
seven o’clock; by which time the vital functions have become so far
exhausted, as to create a strong desire for indulgence in something
stimulating both in food and drink. If this desire be gratified,
immediate relief is obtained, and a temporary feeling of comfort
pervades the frame; but nothing can be more erroneous than to regard
this as a proof of the indulgence being beneficial. The organization
soon gets accustomed to the stimulus; its susceptibility becomes
impaired by the frequency with which the latter is administered; and in
a short time indigestion is the inevitable consequence.
The evils attendant on this course of life are not unfrequently
aggravated by the preposterous means resorted to for their prevention.
Having some vague notion that _exercise_ improves digestion, and
not being at all aware that there is an improper as well as a proper
time for taking it, many persons, after being exhausted by seven or
eight hours’ confinement to the counting-house, proceed to take a walk
of four or five miles before going home to dinner, and thus utterly
throw away the little strength that was left to them, and are filled
with disappointment on finding their appetite and digestion worse than
before.[38] Dr Paris mentions the case of a clerk in a public office
who brought upon himself all the horrors of dyspepsia and melancholy by
following this plan. He breakfasted at nine, went to his office at ten,
continued there till five, walked till seven, and then dined. He was
cured in six weeks, by adopting a more rational regimen and dining at
three o’clock.
Many females and delicate persons injure their powers of digestion by
delaying their exercise till the system is too much exhausted to profit
by it. In boarding-schools the same error is often committed from the
desire which is felt to have all the lessons over before allowing any
play.
As a general rule, then, not more than five hours ought to intervene
betwixt breakfast and dinner. If the mode of life be such as involves
great activity in the open air, or the period of life be one of rapid
growth or filling up (as during youth or convalescence from illness),
the interval may with propriety be shortened; whereas, if the mode of
life be sedentary, and unattended with much activity of nutrition, the
interval may be considerably protracted without much inconvenience.
Much, also, ought to depend on the natural rapidity or slowness of
digestion. In some constitutions, chylification goes on so slowly
that the individual can pass with ease eight or ten hours without
food; whereas, in others, it is so rapid that a fresh supply becomes
necessary in half the time. Spallanzani himself was an example of the
former kind; for in him digestion went on so slowly that he was unable
for study till five or six hours after even a very spare dinner. The
proper rule in every case is, to take dinner at such an interval after
breakfast as the return of healthy appetite indicates, whether that
interval be longer or shorter than the average specified.
That, according to this rule, the _general_ time for dinner
ought to be somewhere about five hours after an ordinary breakfast,
is evident from the almost universal return of appetite at the end of
such an interval, and from the fact that many, through sheer inability
to resist longer the wholesome cravings of nature, are in the regular
practice of eating dinner at that time, but to save appearances give
it the name of _luncheon_; by which means they hold themselves
entitled to the enjoyment of a second and more substantial dinner later
in the day.
Invalids, dyspeptics, and all who, possessing vigorous digestion, wish
to retain it, will do well to follow the intentions of Nature, and
observe the intervals which she has appointed. Those who disregard
them, and still digest without difficulty, have reason to be grateful
to Providence; but they may rest assured that they will longer enjoy
their privilege, and better evince their gratitude, by submitting their
conduct to the ordinary laws of the animal economy, than by presuming
too much on their supposed exemption from the salutary restraints of
reason and experience.
Supposing nine o’clock to be the hour of breakfast, the natural
dinner-hour would thus be two o’clock; and such, accordingly, is that
sanctioned by the most extended experience, and which ought to be
adhered to by all whose occupations will admit of its observance, and
who wish to enjoy the highest health of which they are susceptible.
Artificially arranged, however, as society now is, whole classes of the
community find it impossible to dine till much later in the day. The
question then comes to be--As we cannot follow the system laid down
by Nature, what is the next best to be done? Ought we to eat nothing
till we can find time to dine at five, six, or seven o’clock; or ought
we rather to take a light meal at the natural time, about one or two
o’clock, and reserve our appetite chiefly for the substantial meal
which we have leisure to digest?
The principle in virtue of which digestion is interrupted by bodily
or mental labour occurring after a full meal, having been already
sufficiently explained, it needs scarcely be added, that the second
is the better plan, and moreover that by leaving the stomach too long
empty we risk impairing its functions, and weakening the system.
When dinner cannot be taken earlier than seven or eight hours after
breakfast, most people will find it advantageous to partake of some
slight refreshment in the mean time--enough to blunt the keenness
of appetite, but not entirely to destroy it. When the individual is
exposed to much bodily exertion in the open air, or is at the period
of rapid growth, a portion of animal food, or an ordinary luncheon,
taken in moderation, may be allowable, and even requisite; but where
the habits are sedentary and the constitution formed, a bit of bread
or biscuit and a glass of water will be far more serviceable. Many
people, from want of any better occupation, make a pastime of filling
their stomachs every forenoon at the pastry-cook’s, with as little
regard to its powers and necessities as if digestion were meant merely
as an appendage to taste; and think themselves entitled to complain
of their defective appetites, and the great discomfort which attends
the subsequent ingestion of a heavy dinner. To relieve the weakness,
arising not from exhaustion but from the oppression of satiety, they
resort to wine, as if by adding fuel to the fire they could hope to
extinguish the flame!
Even in fashionable life the superiority of Nature’s arrangements over
those of man is so far acknowledged, that it is an almost universal
rule for children to dine in the middle of the day; and there cannot
be a doubt that the practice is attended with manifold advantages to
the young, although, as regards their moral training, these would be
greatly increased were they to associate at meals with their parents,
instead of being left entirely to the company and management of
servants.
Here I cannot refrain from earnestly soliciting the attention of the
reader to the injury inflicted on the young by the irrational mode
of life and education to which they are now subjected. As growth and
nutrition are in them in their highest activity, it follows that at no
period of life is strict adherence to the laws of the animal economy
of so much moment, because if the youthful system does not receive at
the proper intervals the supplies of food of which it stands urgently
in need, it must necessarily be impaired in tone, and become more
liable to the inroads of disease. The completed and compact frame of
an adult may resist for a time irregularity in its supplies; but the
undeveloped and susceptible organization of the young, suffers from
the very first, and the evil increases in proportion as the aberration
from the order of Nature is repeated. Hence reason, affection, and
enlightened benevolence, all concur in enforcing a strict adherence to
an early dinner hour for the young. And yet, if we examine the customs
of society, especially in the middle and higher ranks resident in
towns, we find the school occupations so irrationally arranged, that
while the children are obliged to breakfast early, even in winter, to
reach them in time, most of them find it impossible to dine till five
or six o’clock--_eight_ or _nine_ hours after their first
meal, instead of _four_ or _five_. And when feeble digestion,
delicacy, or bad health result as the natural consequence of our insane
proceedings, instead of blaming our own folly and amending our conduct,
we sit down complacently to lament the degeneracy of the age, and
boast of the marvellous constitutions and hardihood of the children of
_our_ day, whom neither wind nor weather could hurt. If it were
a favourite colt or dog whose training we were superintending, the
folly of shutting it up all day in a confined atmosphere and denying
it food at proper intervals, would stare us in the face. But in our
vain conceit, we cannot bring ourselves to admit that our bodies grow
and thrive under the influence of the same general laws by which
those of animals are regulated; and are better pleased to receive the
chastisement due to our ignorance and pride in the shape of disease and
death, than to inquire into the will of God towards us, and bow to it
in submissive meekness, and well-founded hope.
The evil, however, is the source of much suffering and disappointment,
and as it cannot be corrected until the public is rendered fully aware
of its existence and influence, it cannot be too often brought under
its notice, or too strongly condemned. The teacher alone has not the
power of providing a remedy. The concurrence and co-operation of the
parent are indispensable; but both combined could easily effect such
a distribution of the time and business of the school, as to leave
at least a couple of hours in the middle of the day appropriated to
dinner and play after it in the open air. It is no valid objection to
say that in winter the day is too short to allow the “sacrifice” of so
much time. The shorter it is, the greater is the necessity for making
the most of it by adequate attention to the laws of health. The real
“sacrifice” of time is when health is impaired and progress retarded
by undue confinement and deprivation of exercise in the open air. The
very shortness of the day, indeed, implies that we should employ the
hours of darkness in _in-door_ occupations, and make the most of
the daylight by going out while we have it; and I have no doubt that as
society advances, this truth will be felt and acted upon to the great
advantage and delight of the young.
Supposing it to be made an imperative condition of our social existence
that we shall rise after mid-day, and not go to bed till a late hour in
the morning, the present fashion of dining at seven or eight o’clock
becomes much more rational than is commonly imagined by those who
declaim against it without regard to the concomitant circumstances.
It is, no doubt, most absurd and hurtful for a man who rises at seven
or eight o’clock, breakfasts at nine, and goes to bed at eleven, to
delay dining till seven in the evening; but it by no means follows that
seven is a bad dinner-hour for a person who rises at twelve or one
o’clock, breakfasts at two, and goes to bed at three in the morning.
The interval between the breakfast at one and dinner at seven o’clock,
is the same as between breakfast at nine and dinner at three, namely,
six hours--which is little more than enough. The error lies, not in the
hours chosen for meals, but in the utter perversion of the whole system
of living, by which night is converted into day, and the business of
life is postponed five or six hours beyond the time appointed by the
Creator for its performance. So far from the late dinner being hurtful
in such circumstances, it is only the stimulus and support which it
affords that enables the victims to withstand the fatigue even for a
single week.
No one has a stronger sense of the injury done to society by the wide
departure from the laws of Nature by which its present arrangements are
characterized, and no one is more willing to contribute all that is
within his power to reform them, than the writer of these pages; but
let the whole system be amended, and do not limit the reform simply to
altering the hour of dinner, while the conditions which have led to the
existing arrangement are left unchanged.
In the country, even among the higher classes, a greater approximation
to the order of Nature is observable than in towns. The inducements to
sleep away the day and to be awake during the night are diminished;
bodily exercise and exposure to the open air are more indulged in;
the appetite becomes keener, and digestion more vigorous; and, as
a necessary result, meals are taken an hour or two earlier. But,
throughout all these changes, the general feature of having some kind
of refreshment, either luncheon or dinner, within four, five, or six
hours after breakfast, may be pretty accurately traced.
If business admits of it, and the person can then command two hours
of relaxation, the best plan, unquestionably, is to dine about five
or six hours after breakfast. But if this be impossible, and active
exertion of mind or body must be continued for several hours longer,
it will be far better to eat some light refreshment in the forenoon,
and to postpone dinner not only till business is over, but _till half
an hour or an hour’s repose has allowed its attendant excitement or
fatigue to subside_. By this means the stomach will enter upon its
duties with vigour, and the dinner be digested with greater comfort and
dispatch than if we sit down to table the moment our work is finished.
In this way the tedious quarter of an hour, preceding the announcement
of “_dinner_,” is far from being lost to the subsequent digestion.
Very few people indeed can eat a good dinner and return immediately to
bodily or intellectual labour with continued impunity. On this account,
actors, for example, whose vocation requires exertion of both mind and
body, almost all either dine very early, or take their chief meal at
night on their return home, the latter being the more common practice.
Students, literary men, and persons intently engaged in business, are
very apt to damage themselves by neglecting relaxation at and after
meals.
The time for dinner ought, then, to vary according to the constitution,
occupations, and mode of life of the individual; and the nearer the
whole of these can be made to approximate to the intentions of Nature,
the more vigorous will be the powers of digestion, and the more
complete the nutrition of the body; and, consequently, the more easily
will the stomach recover the tone which it may have lost from previous
mismanagement. In attempting to cure indigestion, notwithstanding the
most scrupulous adherence to the rules given for the proper selection
of food, if we set at defiance all the other conditions of healthy
digestion, our adherence will be of little avail. Whereas, if we fulfil
the laws of our constitution, by rising from bed in the morning,
obtaining a healthy appetite and lively circulation by the regular
exercise of the various functions of mind and body in a free and pure
atmosphere, eating moderately, and enjoying social relaxation after
our meals,--digestion will be so far strengthened, that no very rigid
observance of any particular kind of diet will be necessary; it being
always understood, however, that we shall not exceed in quantity what
the wants of the system require.
It would be a waste of time to discuss gravely whether _tea_
and _coffee_ ought to be allowed in the evening. Custom has
already decided the point, and experience has shewn that, taken in
moderation, they rather promote than impede digestion. When the dinner
is early--say at one, two, or three o’clock--a light meal of tea and
bread in the evening is very suitable, as it saves the necessity of
eating a heavier supper. If the individual be accustomed to much active
exertion in the afternoon, so as to cause considerable waste in the
system, and especially if he be young, a small addition of animal food
may be made with great propriety to the evening meal. But on the other
hand, when the dinner is late, or little exertion is incurred after it,
tea or coffee ought to be used more as a diluent than as a meal.
The French drink a single cup of strong coffee without cream
immediately after dinner, and find digestion go on all the better for
it. It acts as a strong stimulant, and certainly increases the feeling
of comfort for the time. Like all other stimulants, however, its use
is attended with the disadvantage of exhausting the sensibility of the
part on which it acts, and inducing weakness. This inconvenience is
not felt to the same extent indeed after coffee as after spirits, but
still it exists; and it is infinitely better that the stomach should
be brought up to do its own work ungrudgingly, than taught to depend
upon assistance from without; and therefore such assistance ought to
be reserved for the relief of occasional exhaustion, instead of being
resorted to as a regular indulgence. The French partake of a much
greater variety of dishes at one meal than we are accustomed to do,
and may thus require the aid of coffee to keep the stomach from actual
rebellion. But the way to obviate this necessity, is obviously to eat a
more simple and more moderate meal.
A great deal has been said and written about the properties of tea and
coffee as articles of diet. At present, however, we have to do with
them only as elements of a third meal, and must reserve the discussion
of the other branch of the subject to a future opportunity.
* * * * *
In determining whether a third meal ought to be taken either as tea or
as supper, the general principle already laid down will be very useful.
If dinner be sufficiently early to admit of digestion being completed
and the stomach afterwards recruited by repose, and if the mode of life
be active, so as to occasion a natural return of appetite before the
day is done, the propriety of a third meal cannot be questioned. But
if dinner be late, and there be too short an interval between it and
bedtime to admit of digestion being finished and the appetite renewed,
then every additional mouthful swallowed is sure to do mischief. The
farmer who dines at two o’clock, for example, and, after walking about
his fields for three or four hours in the afternoon, comes home in
the evening with a genuine and undeniable appetite, has a legitimate
right to an additional supply of wholesome food before betaking himself
to his couch; because a sufficient interval has elapsed to allow the
stomach to recover itself from the labour of digesting his dinner, and
the continued waste of the system requires to be replaced. In like
manner, the man of fashion who dines at seven o’clock, and frequents
assemblies till three or four in the morning, is well entitled to some
kind of supper about one or two o’clock, and could scarcely get through
his laborious duties without farther sustenance from either food or
wine, or both. Even in his case, six hours may thus intervene betwixt
dinner and supper; and we know that, on an average, the digestion of a
moderate meal is finished in four or five hours. The chief difference
between him and the farmer is, that the farmer reaps health and sound
digestion from adhering in his hours to the institutions of the
Creator, and that the man of fashion impairs his constitution and
enfeebles his digestion--less by the improper intervals at which he
eats, than by his wide departure from the order of Nature in the hours
which he observes.
If, in adopting the precepts of ultra-temperance, we dine early,
live actively, and go to bed with the stomach entirely empty, we
_may_ sleep, but our dreams will scarcely be more pleasant,
or our sleep more tranquil, than if the stomach were overloaded. A
gnawing sense of vacuity is felt in such circumstances, which is apt to
induce restlessness, and nervous impatience and irritability. I have
repeatedly seen these unpleasant symptoms dispelled, and sound sleep
obtained, by no other prescription than a cupful of arrow-root an hour
or two before bedtime.
Except in early life, and in the case of those who lead a very
laborious existence and observe very early hours, supper as a fourth
meal is altogether superfluous, at least where any thing is eaten at
tea. In youth, waste, growth, and nutrition are so active, that a
moderate supper is often indispensable, especially when the muscular
system is freely exercised in the open air. But it ought to be of a
light nature, and taken at least an hour or two before going to bed. If
dinner be taken early, and tea be used in the afternoon, not as a meal
but merely as a diluent, a light supper will be very proper.
In short, the grand rule in fixing the number and periods of our meals,
is, _to proportion them to the real wants of the system, as modified
by age, sex, health, and manner of life, and as indicated by the true
returns of appetite_; and, as an approximative guide, to bear in
mind that, under ordinary circumstances of activity and health, three,
four, or five hours are required for the digestion of a full meal, and
one or two hours more of repose before the stomach can again become fit
for the resumption of its labours. If the meal be temperate and the
mode of life natural, digestion will be completed in from three to four
hours, and one hour of rest will serve to restore its tone; but if the
quantity of food be great, or the general habit be those of indolence,
digestion may be protracted to five or six hours, and two or more be
required for subsequent repose. It is therefore utterly absurd and
inconsistent with the laws of Nature to pretend, as many writers have
done, to lay down rules which shall apply to every individual and to
every variety of circumstances. As already mentioned, rules applicable
to _classes_ may be prescribed, because there is a considerable
similarity in the circumstances of all the individuals comprehended
in each; but even there numerous exceptions must occur, which can be
judged only by the standard of the individual constitution.
The Creator indeed has obviously never intended that we should be bound
down to the rigid observance of a very strict order in diet; but, to
fit us for the ever-varying circumstances in which we are placed, has
wisely and benevolently allowed us considerable latitude, and made
appetite to vary in the extent and earnestness of its demands in
proportion to the waste to which we are subjected for the time. It is
astonishing how rapidly a healthy frame accommodates itself even to
great changes, when temperance is duly observed, and a proper regard is
paid to the intimations of appetite.
In suiting my own mode of life to the circumstances under which I have
at various times been placed, I have repeatedly, even as an invalid,
made sudden changes in the hours of eating, with no further injury
than temporary discomfort; but then I always adhered to the general
principles above insisted on. It was by some of these experiments that
my attention was first drawn to the great influence of the accessary
conditions in retarding or promoting digestion. At one time, on
altering my place of residence from Aix to Marseilles, I changed at
once from breakfasting at eight o’clock, dining at two, and taking
tea in the evening, to breakfasting at eleven, and dining at six. For
the first few days I felt uncomfortable in waiting so long in the
morning; but by following the plan of taking a cup of coffee and a
crust of bread soon after rising, and attempting no considerable bodily
exertion till after breakfast, every feeling of inconvenience ceased,
and the system completely adapted itself to the change. Three months
afterwards I embarked on the Mediterranean, and again passed at once to
breakfasting between seven and eight o’clock, dining about noon, and
taking tea in the evening, which I continued to do for some time after
arriving in Italy. On my way home the hours of eating were never two
days the same, and yet I did not suffer. If breakfast was early I ate
it with relish. If it was late, I had recourse to a biscuit, or some
dried fruit early in the morning, to sustain the system in the mean
time, and was ready for it when it came. In the same way, if dinner was
to-day at one o’clock, I took it when it was offered, and had recourse
to some refreshment in the evening: if to-morrow it was postponed till
eight o’clock, which sometimes happened, the refreshment came in the
forenoon, and a moderate meal was taken in the evening.
In these changes, however, it will be remarked that the laws of
digestion were in reality much less infringed upon as to time than one
might imagine from merely hearing that I dined one day at noon and the
next day at eight o’clock in the evening. At whatever hour the meal was
taken, the real wants of the system were supplied when they manifested
themselves in the form of appetite, and the requisite intervals were
observed. If a substantial breakfast was taken at eight o’clock, then
a corresponding interval elapsed before another meal followed at one
or two. If, again, the morning allowance was trifling, then the real
breakfast followed at an interval correspondingly short, namely, at
eleven o’clock. So also with dinner. And if dinner was at one o’clock,
tea followed at the distance of six or seven hours; whereas, if it came
at six or seven o’clock, a refreshment preceded and nothing followed
it, and the results were comfort and sound digestion. If, however, we
yield unguardedly to the impulse of appetite in travelling, and eat and
drink plentifully instead of temperately, no arrangement of hours that
we can make will render our situation either pleasant or healthful.
While, therefore, it seems to be obvious beyond a doubt, that those
who live according to the laws of Nature and begin their activity with
the morning, should breakfast betimes, dine early in the day, and take
a lighter meal in the evening, and that those who do so will reap a
reward in health and vigour of mind and body, unattainable to the same
extent by those who live differently, and convert night into day,--it
would be not less hurtful than absurd to prescribe the same hours for
meals to all, whatever their hours of activity, and whatever their
modes of life; and I cannot help thinking, that it is the preposterous
attempt to generalize too much, which, losing sight of true principle
and the modifications which it requires in individual cases, has
brought dietetic precepts into disrepute, and led to the belief that
the rules laid down are merely arbitrary assumptions, resting on no
solid foundation in the human constitution, or in the designs of our
Creator.
As experience is the best guide to knowledge, I may be allowed to
add, that, when travelling on the Continent in health and strength,
I suffered more from feverish fatigue and stomachic discomfort,
induced by ignorant infringement of the laws of digestion, than I ever
afterwards did, even from more continued exertion when travelling as an
invalid under a better regulated system of diet. I did not, in either
case, make any exception to the meals which awaited our arrival at the
inns, or to the hours at which they were served. The chief difference
was, that, when well, I ate till my appetite was fully satisfied, under
the notion that, in travelling, a full diet is necessary to enable one
to withstand the fatigue; and that, as an invalid, on the other hand,
I ate more sparingly, and, if the regular meal was much later than
usual, had recourse to biscuit, fruit, or a slice of cold meat, as an
intermediate refreshment, to prevent the stomach becoming exhausted
from too long a fast. Following the dictates of experience, I have long
adhered to the latter plan, and am convinced that few who have tried
both will long prefer the former.