MEANS OF INSURING ADEQUATE MASTICATION
In order to secure the full advantages accruing from the use of the
jaws and their appendages, it is, above all, necessary for them to be
adequately exercised during the period of development. If this is done,
not only will the tendency to dental caries, adenoids, indigestion,
and other evils be greatly diminished, but the masticatory instinct
will establish itself as a permanent force, so that the individual
will tend for the rest of his life to subject even soft foods to
thorough mastication. The tongue, the lips, and the jaws of the newly
born child find their natural exercise at the mother’s breast, and
we should, therefore, do our utmost to get the mother to suckle her
child, the bottle affording neither the same kind nor the same amount
of exercise. If, unhappily, we fail in this, we must see that the teat
of the feeding-bottle is so constructed as to compel the child to
earn his meal by, at any rate, some exercise. This kind of exercise
promotes the growth of the tongue and thus of the jaws, especially of
the mandible. Directly the infant shows a disposition to bite hard
things the instinct should be gratified. We may observe a tendency in
this direction as early as the third or fourth month, and it becomes
more and more pronounced when, the time for the eruption of the teeth
approaching, the gums begin to swell up and to get tender, and saliva
begins to flow from the mouth; it is now, more than ever, necessary to
provide the child with hard substances on which to exercise the jaws
and the gums, and a great deal of the trouble of teething is due to
the failure to recognise this fact. What, then, are we to employ for
this purpose? I am convinced that it is a mistake to rely solely, or
even mainly, upon baubles of ivory, coral, and the like useful though
these may be in their way; it is far better to give the child something
which is not only hard but nutrient and pleasant to the taste,
something which will at one and the same time exercise the maxillary
apparatus, excite the gustatory organs, and provide a certain amount
of nutriment. To this end we may, as the teething time approaches,
give a chop or chicken bone, from which most of the meat has been
removed; by powdering the bone with white sugar or salt we may increase
its attractiveness. From such bones a good deal of nutriment can be
extracted, and this of a kind which is most acceptable to the infant
stomach, for it must be remembered that the young human is in the
main carnivorous. Indeed, since milk is a purely animal diet, all the
mammals must be regarded as essentially carnivorous during the period
of suckling, while man, as already observed, from the time he emerged
from the anthropoid until he learned to cook his food, was throughout
life mainly an animal feeder. Therefore we should not hesitate to allow
the teething infant animal food in the form suggested. Chicken and
chop bones, yielding as they do before the pressure on the gums, are,
moreover, just of the right degree of consistence for the purpose in
view, while they afford abundant exercise for the tongue; ivory, coral,
and the like are, on the other hand, too hard and unyielding, and lack,
moreover, the attractiveness belonging to sapidity.
By thus providing the maxillary apparatus with suitable exercise we
shall do much to facilitate the eruption of the teeth and to favour the
growth of the jaws and their appendages, including the salivary glands,
and so to prepare the mouth for the reception of vegetable food. This
should, of course, not be given till the teeth appear. The order in
which these make their appearance gives some indication as to the
order in which vegetable food should be administered to the child. The
first teeth to penetrate the gums are the lower incisors which appear
from the seventh to the eighth month; then follow the upper incisors
from the seventh to the tenth month. These teeth enable the child to
_bite_, but not, be it observed, to _masticate_, for which function
the molars are necessary. Now the first molars do not appear till the
twelfth or fourteenth month; the second molars not till between the
fourteenth and the twentieth month; and it seems to me certain that
our primitive ancestors could not have obtained starch in any quantity
until they reached this age; at the best, pre-cooking man was but
scantily supplied with starch, and such slender supply as he had
could only be rendered accessible to the digestive juices by vigorous
mastication, which broke up the indigestible cellulose framework in
which all vegetable starch is contained; hence, until the young human
cut his molars, he had little opportunity of securing any starch.
These considerations strongly suggest the desirability of giving but
small quantities of starch before the twelfth month, and though the
facts, that ptyaline appears in the saliva about the time the first
incisors are cut, and that pancreatic juice develops its amylolytic
ferment at the same time, show that the digestive organs are ready for
the reception of some starch at the seventh or eighth month, yet I
believe the quantity should be strictly limited. I am ready to admit
that the modern child may have, indeed probably has, a greater power of
digesting starch than his remote pre-agricultural ancestor; but even
so, I am convinced that we should be on our guard not to over-gorge
infants with this substance. Only a small quantity should be given
before the twelfth month, and it should be gradually increased up to
the twentieth month.
I have said that the pre-agricultural infant was unable to secure
starch in any quantity by means of his incisors. These teeth enabled
him, however, to obtain some soluble nutriment from fruits, and
Dr. Sim Wallace has suggested that the early eruption of the lower
incisors is for the purpose of enabling the infant to pierce the
outer covering of fruits so as to permit him to extract the soluble
contents by suction; and, accordingly, when these teeth are cut we
may allow the child to bite at such vegetable substances as apples,
oranges, and sugar-cane. The latter is a useful article of diet for
children, for it provides soluble saccharide in a diluted form, and
it is advisable that the child should receive his cane sugar well
diluted, for it must be remembered that before the agricultural period
man’s supply of pure sugar was limited to wild honey which, consisting
as it does almost entirely of mono-saccharide (grape sugar and fruit
sugar), is very easily disposed of by the digestive organs. Nowadays,
the less digestible cane sugar (which is a di-saccharide) is very
largely consumed in the undiluted state, in which it is apt to set up
disturbance. When, however, it is obtained by chewing the sugar-cane,
it is diluted both by the water in the cane and by the saliva, and I
should like to see children obtain most of their cane sugar in this way.
The consideration of the conditions obtaining for pre-agricultural man
not only strongly suggests that the young human of to-day should be
given starch in very moderate quantities up to the twelfth month, but
it points an even more important lesson--viz., that this substance
should be given not, as is the custom, as liquid or pap, but in a form
compelling vigorous mastication, for it is certain that early man, from
the time he emerged from the ape till he discovered how to cook his
vegetable food, obtained practically all his starch in such a form;
it cannot too often be repeated that uncooked starch in the natural
state, locked up as it is in chambers of indigestible cellulose, has no
nutritive value; these chambers need first to be broken up by prolonged
and energetic chewing, and in this way much or most of the starch is
converted in the mouth into dextrines and maltose, very little passing
into the stomach in the crude state to set up disturbance in that
organ and later in the bowel. If it is given as liquid or pap it will
pass down as starch into the stomach, while if it is administered in
a form which obliges the child to chew it properly, not only will the
jaws, the teeth, and the gums obtain the exercise which they crave,
and without which they cannot develop normally, but the starch will be
so thoroughly insalivated that much of it will be converted within the
mouth into maltose. How foolish to upset the child’s digestive system
by deluging it with liquid starch, and then to endeavour to correct
matters by giving the malt extract which the child can and should
himself manufacture within the laboratory of his buccal cavity.
Clearly, then, the child should make his first acquaintance with
starch, not in the form of a liquid or pappy patent food, but in a
solid and somewhat tough form. The best means of achieving this end
is occupying my attention, and I hope soon to publish the results of
my investigation. Meanwhile, I would point out that hard, well-baked
crusts constitute a convenient form in which to administer starch to
children. A piece of crust may be put in the oven and re-baked; this
not only hardens it but helps to convert the starch into dextrine,
which is a stage on the road to maltose. If the crust be then cut
into a suitable shape and spread with bacon fat or fresh butter, it
constitutes a most agreeable morsel. Later, we may give hard plain
biscuits. The same principle should be acted upon during later
childhood and youth: we should always give, as far as possible, the
starch in a form compelling abundant mastication. Loaves should be
shaped so as to give a maximum of crust and a minimum of crumb,
and should be baked hard. Such loaves are quite as nutritious as
the ordinary ones, and much more digestible, containing as they do
an abundance of dextrine and not a little maltose, and compelling
efficient mastication, especially if eaten, as they should be, without
any fluid. A lady who has the catering for a large number of girls
gives the bread in this way, and she tells me that there is keen
competition for the most crusty portions.
I do not say that starch in the liquid and pappy form should find no
place whatever in man’s dietary at the present day, for this would
imply the prohibition of porridge, boiled potatoes, milk puddings,
and the like. We cannot put back the hand of time and return to the
food of our primitive ancestors, nor is it desirable that we should;
but we can, at least, arrange matters so that a large proportion
of the starch we consume shall be in a form inviting mastication,
such as crusts, stale bread, stale cake, biscuits, and so forth. The
less children eat of pastry, or, indeed, of any luxurious foods, the
better; if brought up on a healthy dietary and under healthy conditions
generally, they will relish their simple fare more than the choicest
dishes of the epicure. I do not, I say, object to the child consuming
a certain proportion of starch in the liquid or pultaceous form, for
if, by bringing him up on a rational dietary, his instinct to masticate
be afforded due opportunity to develop he will be likely to subject
even soft vegetable food to something like adequate mastication; this
will tend to mitigate the evils associated with such food, not only by
facilitating the digestion of starch, but by flushing the mouth and
promoting the health of the teeth and buccal mucous membrane.
The question how far children should be allowed to crack nuts may here
be considered. If the child has been brought up on pappy food, and has
in consequence brittle and ill-developed teeth, the cracking of hard
nuts will be likely to injure them, and this is _a fortiori_ true if
any of the teeth are carious or “filled.” And not only nuts but hard
food of any kind, such as ship’s biscuits, may in these circumstances
injure the teeth, as many of those who went through the recent South
African campaign can testify. But if, on the other hand, the child has
from the beginning been fed on coarse, hard foods, so that the teeth
have been allowed to grow dense and strong, no harm is likely to ensue
from cracking such nuts as filberts and Spanish nuts. If a squirrel
or a monkey weighing a few pounds can do so with impunity, surely the
young human should be able to also. The cracking should, however, be
done by the molars, while such hard nuts as Brazils had best not be
tackled at all.
Animal food does not need the same amount of mastication as vegetable
food, since it is not digested in the mouth, though some contend that
the mixture of proteid with alkaline saliva facilitates its subsequent
peptonisation. Cooked animal food is, however, all the better for some
mastication, owing to the coagulation of the proteids, and, in order
to insure the efficient mastication of meat, fish, and poultry, Dr.
Sim Wallace recommends that they should be given in large pieces cut
thin. “Flat pieces about one inch square generally _necessitate_ a
certain amount of mastication. It is difficult to swallow large flat
pieces of meat without mastication, but when finely minced little or no
mastication is called forth.” The younger the child the more underdone
should the meat be.
EXAMINATION OF THE MOUTH AND ADJACENT PARTS
If a child be brought up on the lines indicated and under healthy
conditions generally, it is tolerably certain that the maxillary
apparatus will develop normally, that the teeth will be strong and
well opposed, and show little tendency to disease; but, inasmuch as
the methods advocated are but seldom put into practice, disorders of
the teeth, more especially caries and irregularities, are common, and
hence with a view to promote more efficient mastication it is always
advisable to examine our patient’s teeth.
Each individual tooth should be inspected in a good light for the
presence of caries, and careful note should be taken of the “bite,”
a normal bite implying not only a proper opposition of the two rows
of teeth but the capacity of the lower ones to move freely across the
upper; mere vertical movement of the mandible does not constitute
efficient mastication. In this connection it must not be forgotten that
an unopposed molar is useless for purposes of mastication, and it is by
no means rare to find in a mouth several sound unopposed molars which
are for this reason absolutely functionless. Nay, more than this, it
may happen that teeth, perfectly sound ones, too, far from helping, may
actually interfere with mastication; thus, among the poor, we sometimes
find all the teeth gone save the upper canines and the lower incisors,
and the teeth and gums being alike unable to come into contact, nothing
worthy of the name of mastication is possible; it would be far better
to be without any teeth whatever, for the toothless gums would then be
permitted to come into contact along their entire extent, under which
condition they gradually harden and come to be quite efficient grinding
agents.
Next the gums, the alveoli, and the roots of the teeth must be
examined, especially for the presence of erosion, tartar, and pyorrhœa
alveolaris, this latter condition being evidenced by the welling-up of
pus upon pressing the gums against the sides of the teeth.
If our examination of the mouth discloses anything likely to interfere
with mastication the aid of the dentist should at once be sought, but
every physician should be so far acquainted with disorders of the
teeth as to be able to say, in the majority of cases, at all events,
when this is necessary. I am convinced that far more illness than is
generally supposed is attributable to dental defects, and this even
among the more leisured classes. With regard to pyorrhœa alveolaris, it
has to be remembered that it not only does harm by causing loosening,
lengthening, and shedding of the teeth, and thus interfering with
mastication, but also by contaminating the stomach and the blood and
thus upsetting the digestion and causing constitutional diseases, such
as anæmia and arthritis; and inasmuch as poisonous discharges from
the nose, the naso-pharynx, the pharynx, and the tonsils may act in a
similar way, these parts also should be inspected in connection with
the examination of the teeth. In the dust-laden atmosphere of towns
they are very liable to disease, and even when healthy are necessarily
dirtied; some go so far as to advise all town dwellers daily to wash
out the nasal passages and to gargle the throat; but, whatever may be
thought of this, it is certain that under existing dietetic conditions
special means are needed in order to keep the mouth and teeth clean.
When man fed on raw food this was not necessary, the food itself
and the copious flow of saliva, induced by prolonged mastication,
effectually cleansing these parts; but, under present conditions, food
tends to remain within the mouth, especially between the teeth and in
their crevices, and therefore special means are needed to remove it.
This is done by “cleaning the teeth” and by rinsing the mouth.
_The tooth-brush._--Probably the ideal method of cleaning the teeth
is that adopted by many primitive and not a few semi-civilised
peoples--viz., rubbing them with a twig of wood which has been teased
out at one end so as to form a sort of brush by means of which the
teeth can be burnished and food dislodged from them. The modern
tooth-brush requires to be used with great caution, as it is capable of
doing much harm, not only by removing the mucoid film, which, according
to Dr. Wallace, protects the teeth from corroding agencies,[28] but
probably also by injuring the edge of the gum and the neck of the
teeth, and thus setting up the condition known as “erosion.” Certain
it is that some of the best sets of teeth I have encountered have been
wholly unacquainted with the tooth-brush. In any case the brush should
be employed with great care; it should be soft, and should always be
drawn away from the gums both on the inner and outer aspect of the
teeth towards the biting surface, as well as across the latter, never
transversely across the outer surfaces, as so frequently is done. The
object of these procedures is to dislodge any particles of food that
may have collected between the teeth or in their crevices. For this
purpose the toothpick may also be employed judiciously. In order to
render the enamel of the teeth white it is better to rub each tooth
carefully with some soft material, such as chamois leather, rather
than to scrub them with a brush. Tooth-powders should not be used as
a matter of routine, but only occasionally and for appearance rather
than for cleanliness, and should consist of some simple non-irritant
material. Antiseptic powders and washes are to be scrupulously avoided,
for it is neither desirable nor possible to render the buccal cavity
aseptic; myriads of bacteria flourish within it, many of which play
a useful part as scavengers. The time of all others for cleaning
the teeth is just before going to bed, so that the food shall not be
allowed to decompose in the mouth during the night. There will then be
no need to use the tooth-brush in the morning.
_Rinsing the mouth._--The mouth should be rinsed out as a matter of
routine after each meal and on rising, and care should be taken to do
this before the early cup of tea, so as not to contaminate the stomach
with the buccal secretions which have accumulated during the night.
Inasmuch as raw vegetable food has a cleansing effect on the teeth, it
is often a wise plan, especially in the case of children, to finish a
meal with some kind of fruit, such as an apple or an orange. It hardly
seems necessary to insist upon the necessity for keeping all artificial
dentures thoroughly clean.
PROFESSOR PAWLOW’S DEMONSTRATIONS OF PSYCHIC INFLUENCE IN DIGESTION
[In presenting a theory of human alimentation involving mental or
nervous as well as mechanical and chemical factors which influence
it for good, it is not often that an author is able to enlist the
assistance of a complete battery of scientific confirmation to fortify
his own crude observations taken direct from personal experience in
the study of natural requirements.
Professor Pawlow, with his marvellously skilful investigation of the
workings of the digestive secretions, and Dr. Cannon of the Harvard
Medical School, by aid of persistent and patient X-ray studies,
explain how it is that earned appetite and thorough mouth-treatment
of food are preliminary necessities of easy digestion, and that
disturbance or shock of any sort during the process stop digestive
proceedings and endanger health. They show also that when the mouth is
used to do _all that it can do_ in the work of digestion all the rest
is easily accomplished by the NATURAL AUTOMATIC PROCESSES within the
body.
They both show that we have, each of us, a certain responsibility in
the matter of right digestion and healthy nutrition, and that all
this personal responsibility is located in the head, in the mind, and
in the mouth, and that while the alimentation is proceeding it is a
sacred duty to do our part _right_, according to the intelligence that
these most valuable demonstrations teach.
Professor Pawlow has allowed publication of his lectures in Russian
and German, and recently Professor W. H. Thompson of the Physiological
Department of Trinity College, Dublin, has made an English translation
which is issued by Charles Griffin & Company of London and J. B.
Lippincott of Philadelphia.
The author has to express special gratitude to Professor Pawlow,
Professor Thompson, Messrs Griffin and Lippincott for permission to
reprint herein some entire lectures and extracts that bear especially
on the practical understanding of our subject.
Professor Pawlow is one of the Board of Scientific Assessors mentioned
in the REPORT of a PLAN for an INTERNATIONAL INQUIRY into the subject
of HUMAN NUTRITION.
In one of the lectures, not here reprinted, Professor Pawlow gives
merited recognition of the early statements of the French physiologist
Blondlot relative to psychic influence on the digestive secretions
made some half century ago, but discredited by physiologists since
that time, owing to insufficiency of evidence brought forward in
support of the statements.
Professor Pawlow’s acknowledgment is so gracefully rendered that it is
here given as a model of scientific courtesy.
“I have depicted the work of the gastric glands as we have seen it
in our experiments, and as it has developed under our hands. Is the
picture a new one? In its details, yes; but not in its fundamental
features. However singular it may appear, the sketch of this
picture was more than fifty years ago outlined by physiology. May
this constitute another reason for our science relinquishing its
characteristic shyness of new things and for its conversion to our
interpretation of the phenomena under consideration!
“The talented author of the _Traité Analytique de la
Digestion_--Blondlot--spoke in plain words of the importance of taking
food, and of the specific excitability of the gastric mucous membrane.
The facts adduced in the working up of his theory were naturally
insufficient, but we must not forget that the first experiments on
dogs with artificial gastric fistulæ had only just been performed.
It is truly incomprehensible that the researches of Blondlot and his
views upon the secretion of gastric juice have experienced during the
past fifty years no completion, no additions, but, on the contrary,
have passed out of sight, thanks to the faulty experiments and
erroneous representations of later authors. Only in the works of a
few writers--and those mostly French--has Blondlot’s theory survived.
Of other investigators we must give mention to Heidenhain, who has
enriched the physiology of absorption in general, but more especially,
in connection with the secretory work of the stomach, has discovered
many important facts and has given birth to many fruitful ideas. From
him proceed the subdivision of the secretory process according to
periods and exciting agencies, as well as the suggestion that it would
be important to investigate the individual food-stuffs in relation
to the work of the stomach. Heidenhain’s results are contained in
his well-known article on the secretion of the cardiac glands of the
stomach, published in the year 1879 in PFLÜGER’S ARCHIVES. The work of
Blondlot and the additions of Heidenhain comprise almost everything
of importance which was accomplished by physiology in fifty years
concerning the conditions and mechanism of the secretory work of the
stomach during digestion. Full of moment, however, for our subject was
the obvious error that mechanical stimulation constituted an effective
excitant of the gastric glands, and this error was in its turn a
result of faulty methods.”—HORACE FLETCHER.]
LECTURE IV
GENERAL SCHEME OF AN INNERVATION MECHANISM--THE WORK OF THE NERVOUS
APPARATUS OF THE SALIVARY GLANDS--APPETITE, THE FIRST AND MOST POTENT
EXCITER OF THE GASTRIC SECRETION
Constituent parts of a complete innervation mechanism--The special
duty of the peripheral terminations of afferent nerves--The specific
qualities of nerve cells--Analogy between the innervation mechanism
of the salivary glands and that of the deeper-lying glands of
digestion--The exciting agencies of the nervous mechanism of the
salivary glands; their particular properties--Differences between
the exciting agencies of the different salivary glands--Discussion
of the sham feeding experiment--Mechanical and chemical stimulation
of the cavity of the mouth has no effect on the gastric glands--The
experiment of Bidder and Schmidt relative to psychic excitation of
the gastric secretion--Conditions for success in this experiment--The
passionate longing for food--the appetite--alone brings on the
secretory effect in the sham feeding experiment.
GENTLEMEN,--As you have learned in the last lecture, and also in part
have seen by direct experiment, the nervous system can influence the
work of our glands in the most diverse ways. The vagus nerve, already
burdened with many duties, has, in addition, proved itself to be an
undoubted exciter of the gastric glands and of the pancreas. But we
must also assign to the sympathetic nerve a similar _rôle_. This is a
matter which cannot be doubted, so far as the pancreas is concerned,
and is highly probable as regards the stomach. We also saw good reason
for believing that these two nerves contained two different classes
of fibres, secretory and trophic, a condition which had already been
proved to exist by Heidenhain for the nerves of the salivary glands.
As a hypothesis we might even have proceeded a step farther and have
divided Heidenhain’s trophic nerves into separate classes of secretory
fibres. Lastly, we advanced important experimental evidence to show
the existence of special inhibitory fibres to the glands, and these
fibres also run in the vagus, the list of whose functions seems almost
interminable.
We obtained these results by division and artificial excitation of
the nerves which run to the glands. But when, how, and by what means
these nerves are thrown into activity during the normal course of
physiological events remains a question.
In order to avoid repetition, and at the same time impart the utmost
clearness to our representation, it may be useful to bring before your
minds at once the plan of innervation of a given organ, all the more
since this scheme is seldom completely followed out or adequately
described in physiological text-books. Consequently, it is not borne in
mind with sufficient precision by the majority of medical men.
A complete innervation mechanism consists of the peripheral endings of
the centripetal (afferent) nerves, the centripetal nerves themselves,
the nerve cells (a group of nerve cells connected with each other is
termed a “nerve centre”), the centrifugal (efferent) nerves, and,
lastly, their peripheral terminations. Physiology now accepts it as a
settled fact, that nerve fibres serve only as _conductors_ of nervous
impulses, which come in from contiguous links of the nervous chain.
Only the peripheral endings of nerves and the nerve cells themselves
have the power of transforming the external stimulus[29] into a
nervous impulse. In other words, in the intact organism these alone
constitute the normal receiving apparatus of the nervous system.
Whether the peripheral ends of centrifugal (efferent) nerves are
likewise able to function as normal sites for the application of
external stimuli has still to be answered. Consequently, when any
external agency excites the peripheral terminations--the receiving
stations--of centripetal nerves in this or that organ, the effect
of the stimulus will be conveyed through the centripetal nerves, as
through a receiving wire, to the central station--the nerve cells. Here
it becomes changed into a definite impulse and now comes back along the
centrifugal nerves--the outgoing wires.
The utmost importance is to be attached to the fact that only the
peripheral endings of centripetal (afferent) nerves, in contrast to
nerve fibres themselves, respond to _specific_ stimuli; that is to
say, are able to transform definite kinds of external stimuli into
nervous impulses. The function of the end organs with which they are
connected is therefore of a purposive nature; in other words, these
organs are only called into play by certain definite conditions, and
impart the idea of being aware of their purpose, of being conscious
of their duty. We have long known that the peripheral endings of
sensory nerves are possessed of a high degree of speciality, and cannot
therefore have any doubt regarding the specific nature of the end
organs of other centripetal nerves. This is a sore point in present-day
physiology. But, notwithstanding our knowledge of the separate parts
of the animal body, we shall only be able to form a true conception
of the motive agencies of the whole complicated machine, when we have
established the specific excitability of the end apparatus of every
centripetal nerve, and have discovered all the mechanical, chemical,
and other factors which throw this or that end apparatus into an active
condition. I always look upon it as a period of scientific inadequacy
so long as the effects of the most diverse external agencies upon any
normal physiological process are admitted to be indistinguishable. As
the work of the digestive canal is now represented in the majority of
text-books, and consequently presented to the mind of the physician,
it bears the impress of this period. To impart to the physician a more
correct conception of this matter was my chief object in giving these
lectures. I hope, indeed, to furnish you with evidence sufficiently
convincing, that the alimentary canal is endowed not with mere general
excitability; that is to say, does not respond to every conceivable
form of agency, but only to special conditions which are different
for the different portions of its length. Just as men and animals in
the world are only able to maintain their existence and constantly
adapt themselves to changing circumstances by aid of the peripheral
endings of their sensory nerves, so every organ, indeed every cell
of every organ, can only maintain its place in the animal microcosm,
and adapt itself to the activity of innumerable associates, as well
as to the general life of the whole, by virtue of the fact that the
peripheral end apparatus of its centripetal nerves possesses a specific
excitability.
The same applies to the nerve cells: obviously they are endowed
with specific sensibility. Irrespective of the excitations which
are communicated to them from centripetal nerves, they respond, as
originators of nervous impulses, only or at least mainly to definite
forms of mechanical, chemical, or other stimuli arising in the
organism. This follows not alone from a number of physiological facts
but also from various pharmacological data. Thus we learn that various
drugs excite or annul the activity of definite portions of the nervous
system, at least in the earlier phases of their effects. This specific
excitability of nerve cells, just as much as the same property of
peripheral end organs, lies at the bottom of the purposive action of
these organs.
Hence, our next duty is to endeavour to discover the normal exciting
conditions of the centripetal nerves belonging to the glands which
we had under consideration in our last lecture, or, more correctly,
to find out the conditions which excite the centres, as well as the
peripheral endings of the different nerves, which form parts of the
nervous apparatus of these glands. We have, therefore, for each phase
of the work of secretion, to find out that portion of the nervous
mechanism which is for the time being under excitation, and to
discover the primary agency by which this condition is elicited. This
would include an exact analysis of the stimulating influence which
mastication and food exert upon the nervous mechanism of these glands.
We shall also be able more fully to comprehend the inner mechanism
underlying the facts which formed the subject of the second lecture.
This, of course, is an ideal programme which we can only follow out
as far as the present state of physiology permits. It may now be
instructive, and, for our further conclusions, advantageous, to glance
shortly at the nervous control of the salivary glands.
The salivary glands, whose innervation has long ago been investigated,
have generally been accepted as types of the deeper-lying digestive
glands, and when it became necessary to form a conception of the mode
of activity of the latter, medical science resorted to a bold analogy
and thought of the nervous apparatus of the salivary glands. But
the attempts of investigators to apply rigidly to others the scheme
of innervation which holds good for the salivary glands, have done
considerable harm to the usefulness of the analogy and have prevented
our arriving at a correct idea of the plan of innervation of the
abdominal glands. We have already had an example of this nature before
us. In the salivary glands we have no clearly marked indications of
nervous inhibition, and this circumstance has decidedly retarded
the due development of our knowledge of the nervous control of the
abdominal glands. Authors naturally expected to see a simple and
prompt stimulation-effect from the same conditions of experiment which
sufficed for the salivary glands, and the failure of this gave them,
as they thought, the right to deny the existence of any extrinsic
nervous influence upon the abdominal glands. The error is now obvious;
the abdominal glands behave in some ways different from the salivary
glands, and for their successful investigation, other conditions of
experiment are necessary than those which held good for the former. In
the working of the abdominal glands nervous inhibitory processes play
a large part, but they are almost wholly absent in the case of the
salivary glands. This is an additional warning that one must never push
the conclusions drawn from analogy too far, but must constantly bear in
mind that the life-functions of all organs are extremely complicated,
and that the work of even the most apparently similar organs should
be submitted to separate and careful observation. To me it appears
that the unjustified analogy drawn between the abdominal and salivary
glands has to be credited with another important misapprehension.
And precisely for this reason I think it desirable to bring under
consideration, if only in brief fashion, the conditions of work of the
salivary glands, especially since Dr. Glinski has instituted in the
laboratory some easily performed experiments which bear upon the matter.
The experiences of daily life teach us from the outset, that the
activity of the salivary glands begins even before the introduction
of food into the mouth. With an empty stomach, the sight of food or
even the thought of it is sufficient to set the salivary glands at
once into activity; indeed, the well-known expression, “to make one’s
mouth water,” is based upon this fact. Hence a psychic event, the eager
longing for food, must be accepted as an undoubted excitant of the
nervous centre for the salivary glands. On the other hand, the same
every-day experience, as well as numerous experiments upon animals,
teach us that a number of substances, when brought into contact with
the mucous membrane of the mouth, are likewise able to call forth a
secretion of saliva. One even acquires the impression that everything
brought into the mouth may reflexly influence these glands, the only
difference being a gradual shading off in the effect, dependent upon
the strength of the stimulation which the substance introduced is able
to exert, and it appears to me that it is precisely this impression
which has driven the idea into the background, that the peripheral
end apparatus of the centripetal nerves of the digestive canal are
specifically excitable. The facts were here correctly observed, but
their indications erroneously interpreted.
The great multiplicity of excitants of salivary secretion, has without
doubt, some connection with the complicated physiological functions
of the saliva. This is the first fluid encountered by everything
which enters the alimentary canal. It must, therefore, in a sense
play the part of host to every substance taken in--moisten the dry,
dissolve the soluble, envelop the hard and bulky with mucus in order to
facilitate its passage down the narrow œsophagus; and submit certain
forms of food material, such as starch, to a process of chemical
elaboration. Nor is its duty by any means ended here. The saliva is
secreted in the first compartment of the alimentary canal, which is at
the same time the sorting-room of the organism. Much of what enters the
mouth may prove in the testing process to be useless, or even noxious,
and must either have its deleterious properties neutralised or be
completely rejected. The saliva is secreted in the first instance to
obviate injurious effects in some way; thus, for example, a strong acid
is to a certain degree neutralised, while other corroding substances
may be simply diluted, and by mere reduction of concentration have
their harmfulness diminished.
In the second place, when the injurious substances have to be wholly
removed, the saliva plays the _rôle_ of a washing-out fluid; otherwise
the material, by clinging to the mucous membrane of the mouth, might in
longer or shorter time gain entry into the blood and there develop its
noxious influence. This last function of the fluid is hardly taken into
account at all in physiology, and yet it is evident that the saliva,
as a cleansing fluid, must have a wide importance. If you only think
of how often we are impelled to expectorate, that is, to wash out the
mouth with saliva after something unpleasant, this will be clear.
Such a view finds additional support when we reflect that a feeling
of disgust produces almost as strong a flow of saliva as the sight
of a tasty meal. In both cases the secretion performs the office of
forerunner: in the first it prepares for the washing out of the mouth,
in the second for the requisite elaboration of the food. Think how
often, when something disagreeable enters the mouth, with what rapidity
the saliva is poured out, even after the unpleasant substance has been
for a considerable time removed, and not a trace more is apparent to
the sense of taste. Indeed, long afterwards one has only to recall
the circumstances to mind in order to bring on anew the secretion of
saliva. Apparently the psychic excitation of the nerves of salivary
secretion also ushers in the act of vomiting, which, as is well known,
can be called forth by mental influence. Further, the function of the
saliva just mentioned is probably the true physiological explanation of
the feeling of disgust which many persons experience at the sight of
the secretion itself.
Hence I hold that substances which obtain entry to the mouth set up a
secretion of saliva only because we have here the seat of a definite
physiological sense, and not because the peripheral terminations of the
buccal nerves are devoid of specific excitability, and capable of being
thrown into action by every desired form of stimulus. In other words,
the specific excitability of the peripheral endings of the salivary
nerves is very comprehensive and widely extended. This is no picture
of the imagination, for it can be supported by facts. To say nothing
of the testimony of earlier authors, that the salivary glands have
each particular exciting agencies to which they specially respond, we
can demonstrate the following facts from the material collected in our
laboratory.
Dr. Glinski isolated the orifices of the salivary glands in dogs with
portions of the adjoining mucous membrane, brought them out of the oral
cavity, and caused them to heal into the edges of the skin wounds. In
his first animal the ducts of the submaxillary gland were thus led
outwards. By means of a Mendeljeff’s clip, the wide end of a conical
funnel of waterproof material was attached to the skin surrounding
the orifice. To the narrow end a small test-tube, which served to
collect the saliva, was attached by a wire. I now offer such an animal
a piece of flesh, and, as you see, the tube fills up at once with
saliva. I stop tempting the dog, hang on a new test-tube, and give it
a few pieces of flesh to eat; once more a strong secretion of saliva
results. A new tube is now attached to the funnel, the dog’s mouth is
opened, and a pinch of fine sand thrown in; again there is a flow of
saliva. Once more a new test-tube; and now I apply to the buccal mucous
membrane, the plume of a feather dipped in acid solution, with the
result that I obtain a strong flow of saliva. One may employ a number
of substances in this way, when a similar effect is always produced.
You see, in this, such a comprehensive excitability of the innervation
apparatus of the salivary glands that you might readily interpret it as
meaning the power of response to all and sundry forms of stimulation.
We now proceed, however, to another dog, whose parotid duct has in
a similar manner been diverted outwards. The saliva is collected in
the same way. We tempt the dog with a piece of flesh, but to our
astonishment no saliva flows, and yet the animal is most eager for the
savoury meal offered. Now we give it some raw flesh to eat; again the
secretion of saliva is as good as absent; only when I come near can I
detect one or two drops of saliva running down the sides of the tube.
Probably you will say there is something wrong, either with the method
or with the glands of the animal. But wait a little. I now give the dog
finely powdered dry flesh, and obtain at once an abundant secretion.
Should any one happen to think that the variation in the result is
dependent, not on a different specific activity of the glands, but on
individual differences in the dogs, I respond that Dr. Glinski has had
an animal with double parotid and submaxillary fistulæ, and was able to
observe on one and the same dog, a like behaviour on the part of the
glands to that which we have just seen in two different individuals. An
analogous experiment with bread was also carried out by Dr. Glinski.
The eating of fresh moist bread produced no secretion worth mentioning,
while dry bread, on the other hand, caused the saliva to flow in large
quantities. The results of this experiment permit us to draw extremely
instructive conclusions. In the first place, the several salivary
glands are, as a matter of fact, very sharply differentiated in the
conditions necessary for their activity--that is to say, in respect
to the agencies which excite their nervous mechanisms. Secondly, the
innervation apparatus of the parotid manifests a very sharp selective
power in the choice, so to speak, of an adequate stimulus. The
mechanical effect of large pieces of flesh is naturally much greater
than that of the finely powdered material, and yet it was precisely
to the latter that the glands responded. The stimulus is, therefore,
not due to the mechanical, but to some other property of the food.
This other property is obviously the dryness of the material. Our
example illustrates how that which we may term “purposiveness” comes
into play in the working of our glands and also how erroneous is the
opinion that the mechanical stimulus is all potent. Indeed, previous
authors have already pointed out that dry substances cause a specially
free secretion of saliva, and yet physiological opinion throughout the
length and breadth of the land, as expressed in text-books, has chosen
to recognise a _universal_ instead of a _specific_ excitability. Dr.
Wulfson, who is at present carrying on the investigation of salivary
secretion in our laboratory, has added a very interesting observation
to the results of Dr. Glinski already related. The parotid gland, which
is hardly, if at all, excited when one offers fresh meat to the animal,
responds with a very active secretion, when dry food (bread or powdered
meat) is offered. This phenomenon is all the more surprising since the
desire of the animal for eating is much more strongly excited by flesh
than by dry bread. I am quite convinced that an exact study of the
exciting agencies of the three salivary glands will furnish a number of
new data bearing upon the question in hand.
The second reagent which is poured out on the raw material in the
digestive canal is the gastric juice. How, in the normal course of
events, is the work of the gastric glands, which prepare this juice,
called into play? With the first, and manifestly important factor,
which has a relation thereto, you are already acquainted, and, indeed,
have already seen. I refer to the production of gastric juice in the
empty stomach, as a result merely of the swallowing of food in the
so-called sham feeding of an œsophagotomised dog. When one takes
into consideration the absolute independence of this factor, and the
intensity of the effect, which makes itself evident in the secretion of
a large quantity of juice of high digestive power, the exciting agency
which brings about such secretion must be recognised as one of the most
important and effective processes in gastric digestion. But in what
does it consist? At first sight it appears--and when I previously drew
your attention to the fact I expressed the opinion--that there is here
a simple reflex effect from the cavity of the mouth upon the secretory
nerves of the stomach, similar to the reflex excitation, _e.g._, of the
parotid gland, by finely powdered flesh thrown into the mouth. Now,
however, I assert quite emphatically that this is not the case. We
have, it is true, in the activity of the salivary glands an analogous
phenomenon to indicate--not, however, that of which we have just
spoken. We might apply every conceivable form of stimulus which could
possibly come into play in the act of eating, and yet would not obtain
the slightest indication of secretory activity in the stomach. In this
dog with a gastric fistula, and with also a divided œsophagus, I will
try such an experiment, using the most effective chemical stimulus to
the buccal mucous membrane, viz., acid solution.
The secretion of saliva begins at once, as you see; the acid is,
therefore, effective. From the stomach, however, in spite of continued
excitation, no secretion results, although the acid, mixed with the
saliva, is swallowed and flows out again from the upper segment of the
œsophagus--that is to say, passes along precisely the same path that
the food takes in sham feeding.
We could experiment in the same way with a number of other substances:
saline, bitters, pepper (strong local excitation), mustard, and so
on, and always with the same results; a free secretion of saliva, but
perfect quiescence of the gastric glands. We may even, with the same
object, employ the soluble constituents of flesh in the form of a
decoction, and likewise observe, in most cases at least, no sign of
activity on the part of the gastric glands.
With the chemical we may also combine a mechanical stimulus. We can,
for example, wipe out the mouth with a sponge soaked in the solution
to be experimented with, but always with the same negative result.
We may finally give such pieces of sponge, or even smooth stones of
considerable size, to the dog to swallow, passing them back behind the
anterior pillars of the fauces and allowing them to fall out again,
from the upper portion of œsophagus. It may be added that a well-taught
dog puts up with all these procedures without the slightest protest.
You see that all the manipulations in this case are carried out with
bare hands and without instrumental aid. One can easily train a dog
to swallow stones which are placed in the anterior part of the buccal
cavity. It simply makes a few chewing movements and swallows them down.
The dog on which the acid experiment has just been made serves also for
the swallowing of the stones. The attendant now places some pebbles in
the front part of the mouth, when the animal rolls them round, as if
chewing and gnawing them, and then swallows them. The stones fall out,
as you see, from the œsophagus, and drop with an audible sound upon
the table. This play with the stones has now lasted fifteen or twenty
minutes (in the laboratory we have often kept it up for hours), and yet
not a drop of gastric juice is to be seen.
In order to prove that the dog is perfectly healthy and normal, we lay
aside the stones and proceed to our old experiment of sham feeding. As
you see, the first drop of gastric juice makes its appearance precisely
at the end of five minutes, and after a further five minutes we have
collected more than 15 c.c. of the fluid; consequently there can be no
doubt that in this dog both gastric glands and nerves are uninjured
and function in normal manner. At one time we even had a dog which
voluntarily took the stones out of one’s hand and swallowed them; the
sagacious creature had seen our object in previous experiments and
learned to perform it of its own accord! But in this case also the
result was negative.
Clearly, therefore, neither chemical nor mechanical stimulation of
the buccal mucous membrane is capable of reflexly exciting the nerves
of the stomach. Further, it is obvious that the excitation of these
nerves in sham feeding is not the result of a stimulation coincidently
produced; that is to say, the excitement of the chewing and swallowing
centres does not imply simultaneous action of the secretory centre of
the gastric glands. In what, then, does this influence consist which
is intrinsic to the sham feeding, but which we have not been able to
reproduce in our analytical investigation? There is only one thing
to think of, namely, the eager desire for food, and the feeling of
satisfaction and contentment derived from its enjoyment.
It has, indeed, been known for forty years, thanks to the experiments
of Bidder and Schmidt, that at times, the offering of food to a
hungry dog, in other words, the excitement of a keen desire for
it, is sufficient to cause a flow of gastric juice from the empty
stomach. We shall presently have occasion to observe the force of this
physiological factor. Here I bring before you another dog, likewise
having a gastric fistula with divided œsophagus. The stomach has been
washed out half an hour ago, and since then not a drop of gastric juice
has escaped. We begin to get ready a meal of flesh and sausage before
the animal as if we meant to feed it. We take the pieces of flesh from
one place, chop them up, and lay them in another, passing them in front
of the dog’s nose, and so on. The animal, as you see, manifests the
liveliest interest in our proceedings, stretches and distends itself,
endeavours to get out of its cage and come to the food, chatters its
teeth together, swallows saliva, and so on. Precisely five minutes
after we began to tease the animal in this way the first drops of
gastric juice appear in the fistula The secretion grows ever stronger
and stronger, till it flows in a considerable stream. After the
lapse of a few minutes we can count the number of cubic centimetres
by tens. The meaning of this experiment is so clear as to require no
explanation; the passionate longing for food, and this alone, has
called forth under our eyes a most intense activity of the gastric
glands. If the experiment be frequently repeated, one can easily
observe that the keener and more eager the desire on the part of the
dog for the food, the more certain and intense is the secretory effect.
In extreme cases there is even a quantitative relationship between this
effect and that of the sham feeding.
Here is an experiment of Professor Ssanozki, in which the secretory
effect of the mere tempting of the animal with the sight of food is
compared with that of sham feeding. A few threads of alkaline mucus
had just escaped from the stomach, and then the excitation of the dog
with flesh was begun. After six minutes the secretion commenced and
continued as follows:
Duration of the flow. Quantity of the juice.
8 minutes 10 c.c.
4 ” 10 ”
4 ” 10 ”
10 ” 10 ”
10 ” 10 ”
8 ” 10 ”
8 ” 10 ”
19 ” 10 ”
19 ” 3 ”
Then followed a sham feeding for six minutes.
Duration of the flow. Quantity of the juice.
17 minutes 10 c.c.
9 ” 10 ”
8 ” 10 ”
It is clear that in this case the tempting, instead of being less
effective than the sham feeding, on the contrary excelled it.
Consequently, the observation of Bidder and Schmidt was perfectly
correct. It cannot, however, be said that it received general
recognition in physiology, or that it was sufficiently appreciated.
There are authors who could never convince themselves of its reality,
and in many physiological text-books it is not once mentioned. By
way of explanation, we shall now consider how this matter must be
dealt with by those who wish to observe the effect. It is only under
certain conditions that it can be seen. Firstly, the animal must be
healthy and vigorous; it must have a perfectly uninjured gastric
mucous membrane; and this, from the description in the case of many
authors who obtained a negative result, was not the case. Secondly,
the success of the experiment, as stated above, is dependent upon the
intensity of the desire for eating, and this, again, is dependent
upon how freely and how long beforehand the dog had eaten, and also
upon what it is tempted with, whether with a dish that excites its
desire or leaves its interest unawakened. It is known that dogs have
very different tastes, just as men have. Thirdly, one may find among
the dogs positively careless, indifferent creatures, incapable of
being perturbed in this way by anything which has not actually reached
their mouths, and patiently waiting till the food is given them. Hence
for success in the experiment, eager, impressionable, and excitable
animals are necessary. Fourthly, one has to reckon with the sense and
cunning of the dog, a factor which is not lightly to be disregarded.
Often the animals perceive at once that they are only being teased
with the food, become annoyed thereat, and turn away offended at what
is being done before them. We must, therefore, so arrange matters as
if the animals were not going to be disappointed but fed in reality.
If attention be paid to these conditions the experiment of “psychic
excitation of the gastric secretion,” as we usually term it, will be
found to be as reliable as the experiment of sham feeding. When one is
occupied for a length of time with the study of the gastric secretion
under different conditions, one becomes convinced of what a dangerous
source of error this psychic excitability may become in the different
experiments. We must constantly fight, so to speak, against this
factor, keep it ever in view, and guard against it. If the dog has not
eaten for a long time, every movement,--the going out of the room, the
appearance of the attendant who ordinarily feeds the animal--in word,
every little triviality may give rise to excitation of the gastric
glands. The minutest attention is necessary in order to avoid such
sources of error, and we should not be far wrong if we said that much
which has been ascribed in former investigations to the effect of this
or that agency was in reality a result of unobserved psychic influence.
Consequently, in order to verify our own conclusions concerning the
effects of this or that condition, we have performed many of our
experiments on sleeping animals, having beforehand convinced ourselves
by frequent repetition that sleep exercises no restraining influence on
the working of the gastric glands.
When we recall to mind the failure of our attempts to obtain a
secretion of gastric juice by any stimulation whatever of the buccal
mucous membrane, and at the same time see how constant and intense the
action of this psychic impression is, we are forced to the inevitable
conclusion that in our sham feeding experiment the whole secretory
effect is due to the psychic stimulus, that is to say, to the keen
desire on the part of the animal for food and the satisfaction of
enjoying it.
In view of the importance of the act of eating, which even now is
apparent, but which will become still more obvious when the succeeding
periods of secretion are investigated, we have spared neither time nor
trouble to arrive at a correct explanation of the mechanism of this
factor. We have, therefore, taken in hand a number of modifications of
the sham feeding experiment, and these investigations have confirmed
the opinion at which we had arrived. If, for instance, the dog has
been prepared by a long fast of two to three days, a very intense
secretion of gastric juice will always be obtained by the sham feeding
experiment, no matter what may be given it to eat, whether boiled or
raw flesh, bread or coagulated egg-white, etc. The dog, however, which
has not fasted, that is to say has been fed fifteen to twenty hours
before, will pick and choose amongst the different foods, eating one
with great greed, tolerating another, and refusing altogether a third,
and, corresponding therewith, the amount and quality of the gastric
juice will manifest wide variations. The more eagerly the dog eats
the more juice will be secreted and the greater the digestive power
which it possesses. The majority of dogs prefer flesh to bread, and
correspondingly less juice will be produced by sham feeding with bread
than with flesh. Sometimes, however, we find dogs which will devour
bread with greater appetite than flesh. In these cases one obtains
more and stronger juice in sham feeding with bread than with flesh.
Here is a case in point: a dog is given boiled meat which has been
cut into pieces of definite size, and the pieces follow each other
at regular intervals of time. The animal eats, but soon, from its
behaviour, you see that it develops no particular greed for the meal,
and this observation is confirmed by the fact that after fifteen to
twenty minutes it ceases taking the flesh. The secretion of juice has
meanwhile either not begun at all, or only after a longer interval
than five minutes, and remains scanty to the end. Now wait till the
secretion has stopped and give the same dog raw flesh, either forthwith
or next day, in pieces of the same size and at the same rate as
before. The raw meat tastes excellently to the dog; it eats for hours
at a time; the secretion of gastric juice begins precisely after five
minutes and is very active. With another dog which prefers boiled to
raw meat exactly the reverse occurs. Broth, soup, milk--towards which
dogs are usually more indifferent than towards solid food--often
produce in sham feeding either no secretion at all or only very little,
although broth, for instance has essentially the same taste as flesh.
It is therefore clear that in sham feeding the psychic effect may
readily become an absolute and independent factor. All the conditions
which we enumerated above, and which are necessary for the successful
production of the psychic effect, hold good in combined form for the
sham feeding experiment. The dog eats with greed before one’s eyes;
the food which it receives is pleasant; it not only imagines food but
actually eats it, and has therefore no reason to feel offended, for
naturally the idea does not occur to any of the dogs that all their
trouble is in vain.
Consequently, in the sham feeding experiment, by the act of eating,
the excitation of the nerves of the gastric glands depends upon a
psychical factor which has here grown into a physiological one, that
is to say, is just as much a matter of course, and appears quite as
regularly under given conditions as any other physiological result.
Regarded from the purely physiological side, the process may be said
to be a complicated reflex act. Its complexity arises from this, that
the ultimate object is attained by the joint working of many separate
organic functions. The material to be digested--the food--is only found
outside the organism in the surrounding world. It is acquired not
alone by the exercise of muscular force, but also by the intervention
of higher functions, such as judgment, will, desire. Hence the
simultaneous excitation of the different sense organs, of sight, of
hearing, of smell and taste, is the first and strongest impulse towards
the activity of the gastric glands. This especially applies to the two
latter senses, since they are only excited when the food has already
entered the organism, or at least has arrived very near it. It is by
the establishment of this passionate desire for eating that unerring
and untiring nature has linked the seeking and finding of food with the
commencement of the work of digestion. That this factor, which we have
now carefully analysed, stands in closest connection with an every-day
phenomenon of human life, namely, appetite, may easily be predicated.
This agency, which is so important to life and so full of mystery to
science, becomes here at length incorporated into flesh and blood,
transformed from a subjective sensation into a concrete factor of the
physiological laboratory.
We are therefore justified in saying that the appetite is the first
and mightiest exciter of the secretory nerves of the stomach, a factor
which embodies in itself a something capable of impelling the empty
stomach of the dog in the sham feeding experiment to secrete large
quantities of the strongest juice. A good appetite in eating is
equivalent from the outset to a vigorous secretion of the strongest
juice; where there is no appetite this juice is also absent. To restore
appetite to a man means to secure him a large stock of gastric juice
wherewith to begin the digestion of the meal.
LECTURE V
PERIOD OF OCCURRENCE AND IMPORTANCE OF THE PSYCHIC OR APPETITE JUICE
IN THE SECRETORY WORK OF THE STOMACH--THE INEFFICIENCY OF MECHANICAL
STIMULATION OF THE NERVOUS APPARATUS OF THE GASTRIC GLANDS
The psychic secretion is the normal commencement, in the majority of
cases, of secretory activity on the part of the gastric glands. If
the meal be subdivided and administered at intervals, the psychic
juice appears each time--Demonstration of “appetite juice” in a dog
with an isolated gastric _cul-de-sac_. The work of the gastric glands
if appetite juice be avoided by introducing food through a gastric
fistula unperceived by the animal--Digestion of flesh by the stomach
with and without sham feeding--Duration of the secretory influence of
sham feeding--After the cessation of the psychic effect, how is the
secretory work of the stomach maintained?--Experiments to prove the
ineffectiveness of mechanical stimulation: excitation of the mucous
membrane by means of a glass rod, a feather, a puff of sand, and by
rhythmic dilatation of an india-rubber ball--Contact between the food
and the stomach-wall may indirectly call the activity of the glands
into play by awakening or increasing the desire for food.
GENTLEMEN,--On the last occasion we made ourselves acquainted with
the first normal impulse which, in the natural course of events,
calls into activity the innervation apparatus of the gastric glands.
This impulse is a mental one, and consists in a passionate longing
for food, that which in every-day life, and in the practice of the
physician, is called “appetite,” and which everybody, both medical
and lay, endeavours carefully to promote. We may now venture to say
explicitly, APPETITE IS JUICE, a fact which at once displays the
pre-eminent importance of the sensation. Medical science endeavours to
assist the debilitated stomach by introducing the active constituent of
gastric juice--pepsin--from without, or by prescribing other remedies
believed to promote its secretion. It is, however, of interest to
follow our experimental investigation still farther. What position is
to be assigned to the “psychic” or “appetite-juice”[30] in the course
of normal gastric digestion? Is any definite _rôle_ to be attributed
to it? What course does gastric digestion take when it is absent?
Fortunately to all these important questions satisfactory answers are
forthcoming by experiment. We have only to regret that these answers
come so late.
Let us recall to memory how the secretion of gastric juice proceeded
after feeding with flesh or bread in the case of our dog with the
isolated miniature stomach. The following are the quantities and
digestive capabilities of the first two hourly portions of juice after
the administration of 200 grams of flesh or bread (experiments by Dr.
Chigin):
═════╤═══════════════════╦═══════════════════
│ Flesh. ║ Bread.
Hour.├————————-┬————————-╫—————————┬—————————
│Quantity │Digestive║Quantity │Digestive
│of juice.│ power. ║of juice.│ power.
—————┼————————-┼————————-╫————————-┼—————————
1st │12.4 c.c.│ 5.43 mm.║13.4 c.c.│ 5.37 mm.
2nd │13.5 ” │ 3.63 ” ║ 7.4 ” │ 6.50 ”
————-┴—————————┴————————-╨—————————┴—————————
You see at once that the secretion of the first hour is identical in
the two cases both as regards quantity and digestive power, and only in
the second is the secretory work differentiated according to the nature
of the food. How are we to explain the secretion which takes place at
the commencement? Is it not the same which we have already seen in the
sham feeding experiments? Is not this first onrush of the stream of
secretion the preliminary psychic juice? Unquestionably, gentlemen,
this is the case, and we may convince ourselves of the fact in the
most diverse ways. Above all, the following is clear: whatever occurs
in the so-called sham feeding cannot wholly be absent in the case of
normal feeding, since the former is nothing else than the isolated
commencement of normal digestion. This justifiable inference is fully
confirmed, if the secretion of the first hours after the administration
of flesh and bread be compared with that after simple sham feeding. In
the case of feeding with flesh and bread, the identically similar and
high digestive power of the first hourly portions is striking, and this
power coincides with what we have met in sham feeding. Further, if the
quantity of juice from the miniature stomach during the first hour be
compared with that produced by the non-resected part of the organ,--to
do which we must multiply it by ten, since the resected _cul-de-sac_
is approximately one-tenth of the whole organ,--it is here again found
that the quantity approximately corresponds to the mean values obtained
by sham feeding. Finally, the depression in digestive power or quantity
of juice (with flesh, decrease of digestive power; with bread, decline
in the quantity of juice), which sets in soon after the taking of food,
indicates that the two conditions are connected with the ingestion
of food--_i. e._, with a transitory factor which soon passes away
and gives place to other conditions. Our explanation becomes still
more convincing when we take into consideration the effects of other
foods. If you give the dog, for example, something else to eat which
does not interest it to the same degree as flesh or bread, you will
find the initial increase in quantity and strength of juice does not
appear. Offer the animal milk, for example, which in sham feeding,
especially if it does not last long, calls forth, as a rule, no
secretion, or at all events only very little, and the rapid flow of the
commencement--the already-mentioned initial rise--absolutely fails to
appear. You have already seen the figures which deal with this matter;
I think it necessary, however, to bring them forward again in order
that you may be better able to compare them with the secretion after
flesh and bread.
The dog was given 600 c.c. of milk (experiment by Dr. Chigin).
Hour. Quantity of juice. Digestive power.
1st 4.2 c.c. 3.57 mm.
2nd 12.4 ” 2.63 ”
We have now begun the analytical examination of the variations of our
secretory curve. But owing to the importance of the matter we did not
confine ourselves to conclusions which might be drawn from earlier
investigations. We turned to new forms of experiment for further proof.
Thus we divided the ordinary ration of flesh given to our dogs--400
grams--into four equal parts, which were administered at intervals of
an hour and a half. (Experiments by Privat docent Kotljar and Dr.
Lobassoff.) Each time after the dog received its 100 grams of flesh we
were able to detect a rise both in the quantity and in the digestive
power of the juice. The following table shows the figures in question:
══════════╤═══════════╤═══════════╤═══════════════════════
Half-hour │ Quantity │ Digestive │
periods. │ of juice. │ power. │ Remarks.
——————————┼———————————┼——————————-┼———————————————————————
1st │ 3.1 c.c. │ 5.13 mm. │ 100 grms. flesh given.
2nd │ 5.0 ” │ 4.63 ” │
3rd │ 4.7 ” │ 4.50 ” │
4th │ 5.4 ” │ 4.88 ” │ 100 grms. ” ”
5th │ 5.5 ” │ 3.38 ” │
6th │ 4.7 ” │ 2.75 ” │
7th │ 6.0 ” │ 3.75 ” │ 100 grms. ” ”
8th │ 5.4 ” │ 2.50 ” │
9th │ 5.9 ” │ 2.50 ” │
10th │ 5.4 ” │ 3.88 ” │ 100 grms. ” ”
11th │ 5.3 ” │ 3.0 ” │
12th │ 4.2 ” │ 2.5 ” │
——————————┴———————————┴——————————-┴—————————————————————————
In the curve which follows, only the variations of digestive power are
represented.
It is clear that the increase, both of digestive power and of juice
volume, is connected with the act of taking in food.
It appeared of interest definitely to determine the volume and
properties of the secretion called forth by the act of eating in the
dog with the isolated stomach. We endeavoured, therefore, at the
beginning, to imitate the conditions of sham feeding as they occurred
in the case of the dog with divided œsophagus. In addition to the
fistular orifice leading into the isolated miniature stomach, another
was opened into the main portion of the organ. If we now fed the dog
in the ordinary way with small pieces of flesh, these were received
back again at the orifice of the latter fistula, covered with saliva.
Precisely as in sham feeding, after five minutes the juice began to
flow simultaneously, from both the large and small stomachs. The
secretion ran a corresponding course in the two cavities and ceased at
the same length of time in both after the administration of food was
stopped. Here is an instance taken from such an experiment performed by
Dr. Lobassoff.
[Illustration: FIGURE 1.--Curve of digestive power constructed from the
foregoing table.]
In five minutes the dog had eaten eighty pieces of flesh (weighing 172
grams), all of which soon afterwards dropped out at the fistula. The
secretion began in both stomachs after the lapse of seven minutes from
the commencement of the feeding, and proceeded as follows:
══════╤═══════════════════════╦══════════════════════════════════
│ Miniature stomach. ║ Main stomach.
├——————————-┬———————————╫—————————————┬————————————————————
Hour. │ Quantity │ Digestive ║ Quantity of │ Digestive power.
│ of juice. │ power. ║ juice. │
——————┼——————————-┼——————————-╫—————————————┼————————————————————
1 │ 7.7 c.c. │ ║ 83.2 c.c. │ 5.35 mm.
│ │ ║ │} In consequence of
│ │ ║ │} a mixture with
2 │ 4.5 ” │} ║ 58.1 ” │ } bile (10-15 c.c.)
│ │ }6.25 mm ║ │ } the digestive
2½ │ 0.6 ” │} ║ 8.5 ” │} power was greatly
│ │ ║ │} reduced.
——————┴——————————-┴——————————-╨—————————————┴————————————————————
The secretion from both cavities also came to an end at the same time.
This experiment proves to us, first, that the main and miniature
stomachs work in perfectly parallel manner with each other. The
beginning, the end, and the intermediate variations of the secretion
correspond in both cases. Secondly, the digestive power of the
secretion coincides in both, and is the same which was observed in the
so-called sham feeding. It has here remained at the same height till
the cessation of the secretion, without falling to the lower value
which we observed from the beginning of the second hour onwards, after
normal flesh feeding.
This was also confirmed later, when we performed an œsophagotomy on the
dog, and carried out sham feeding in typical form. Here follows one of
these experiments taken from Dr. Lobassoff’s article.
The first drop of juice appeared from both cavities during the sixth
minute after commencing the feeding, which was kept up for half an
hour. The further course of the secretion was as follows:
══════╤══════════════════════════╦══════════════════════════
│ Miniature stomach. ║ Main stomach.
├————————————-┬————————————╫———————————————┬——————————
Hour. │ Quantity │ Digestive ║ Quantity │ Digestive
│ of juice. │ power. ║ of juice. │ power.
——————┼————————————─┼————————————╫——————————————─┼——————————
1st │ 7.6 c.c. │ 5.88 mm. ║ 68.25 c.c. │ 5.5 mm.
2nd │ 4.7 ” │ 5.75 ” ║ 41.5 ” │ 5.5 ”
3rd │ 1.1 ” │ 5.5 ” ║ 14.0 ” │ 5.38 ”
│———— │ ———— ║ ————— │ ————
│13.5 (total) │ 5.75 (mean)║123.75 (total) │ 5.5 (mean)
——————┴—————————————┴————————————╨———————————————┴———————————
The secretion came to an end in both stomachs at the same time.
The above is represented in curves in Figs. 2 and 3, the scale on which
that for the main stomach is drawn being ten times less than that for
the small. As you see, the progress of secretion is identical in both.
The existence of a fistula leading into the large stomach affords us
also the possibility of performing an experiment upon our dog which
is exactly the converse of the sham feeding experiment, and which
constitutes a real _experimentum crucis_. While in sham feeding, we
had only, so to speak, the beginning of digestion before us, we are
now able in our cross experiment to start at the continuation of this
beginning. For this purpose it is only necessary to bring the food
into the stomach through the fistula, without attracting the dog’s
attention. Since in this experiment it is above all necessary not to
excite the dog’s appetite, it is best to carry out the procedure on the
sleeping animal. I may add at once, however, that the same result can
be obtained on the waking animal, only the process must be performed
unnoticed, and the animal’s attention must be diverted from thoughts of
food.
[Illustration: FIGURE 2.--Curve of secretion from the miniature
stomach.]
[Illustration:
FIGURE 3.--The same from the main stomach reduced ten times.]
The results of this experiment are striking, and do not in any way
resemble the secretion after normal feeding. Some kinds of food, for
instance bread and coagulated white of the hen’s egg, when directly
introduced into the stomach, do not yield a single drop of juice
during the first hour or more afterwards. This holds good both for
the small and large stomachs. When a glass rod is introduced into the
food contained in the organ it remains dry. Flesh, if introduced at
this stage, is able to excite a secretion, but the appearance of the
juice is considerably retarded. It begins from fifteen to forty-five
minutes after the feeding, instead of from six to ten, is under normal
circumstances extremely scanty during the first hour (3 c.c. to 5 c.c.
instead of 12 c.c. to 15 c.c.), and possesses a very low digestive
power.
Here is an experiment by Dr. Lobassoff:
400 grms. of flesh were brought into the stomach.
Hour. Quantity of juice. Digestive power.
1st 3.7 c.c. 2.0 mm.
2nd 10.6 ” 1.63 ”
3rd 9.2 ” 1.5 ”
4th 7.0 ” 1.88 ”
5th 5.6 ” 2.25 ”
6th 6.6 ” 2.63 ”
7th 7.5 ” 1.88 ”
8th 5.3 ” 2.0 ”
9th 3.0 ” 5.0 ”
10th 0.2 ” — ”
The secretion began twenty-five minutes after introducing the food. I
now ask you to compare the following tables:
┌────—┬——————————————————╥——————————————————╥——————————————————┬———————┐
│ │Fed with 200 grms.║Flesh (150 grms.) ║ Sham feeding │ Total │
│ │of flesh (Chigin).║brought into ║ (Lobassoff). │ quan- │
│ │ ║stomach(Lobassoff)║ │ tity │
│Hour.├————————┬—————————╫————————┬—————————╫————————┬————————-┤ in two│
│ │Quantity│Digestive║Quantity│Digestive║Quantity│Digestive│experi-│
│ │of juice│ power. ║of juice│ power. ║of juice│ power. │ ments.│
│ │ c.c. │ mm. ║ c.c. │ mm. ║ c.c. │ mm. │ │
├—————┼————————┼————————-╫————————┼—————————╫————————┼————————-┼———————┤
│ 1st │ 12.4 │ 5.43 ║ 5.0 │ 2.5 ║ 7.7 │ 6.4 │ 12.7 │
│ 2nd │ 13.5 │ 3.63 ║ 7.8 │ 2.75 ║ 4.5 │ 5.3 │ 12.3 │
│ 3rd │ 7.5 │ 3.5 ║ 6.4 │ 3.75 ║ 0.6 │ 5.75 │ 7.0 │
│ 4th │ 4.2 │ 3.12 ║ 5.0 │ 3.75 ║ — │ — │ 5.0 │
└—————┴————————┴—————————╨————————┴—————————╨———————-┴—————————┴———————┘
The progress of juice secretion in the above is also represented in the
following curves:
[Illustration:
FIGURES 4-7.—A. Ordinary curve of gastric secretion (200 grms.
flesh). B. Curve from direct introduction of food (150 grms. flesh).
C. Sham feeding with same. D. Summation of B and C.]
As you see, the curve which represents the results of the direct
introduction of flesh ascends much more slowly and does not attain
anything like the height of that caused by normal feeding with the same
food. But if the quantities obtained by direct introduction of the
flesh be added to those of sham feeding, the resulting curve is almost
identical with the normal.
In like manner the digestive power of the secretion in the foregoing
experiments can be dealt with, and with the same result. It is a good
instance of how a secretion curve can be synthetically constructed from
its constituent factors.
Finally, I am able to demonstrate to you the following instructive
experiment. In the presence of some of my listeners, whom I had invited
to attend an hour before the lecture, I carried out the following
procedures on two dogs, both of which had ordinary gastric fistulæ and
were, besides, œsophagotomised. Into the stomach of one, while its
attention was distracted by patting and speaking kindly to it in order
to avoid arousing any thoughts of feeding, a definite number of pieces
of flesh were introduced through the fistula. The morsels were threaded
on a string, the free end of which was fastened to the fistular cannula
by inserting a cork. The dog was then brought into a separate room and
left to itself. A like number of pieces was introduced into the stomach
of the other dog in the same way, but during the process a vigorous
sham feeding was kept up, the animal being afterwards left alone. Each
dog received 100 grams of flesh. Since then an hour and a half have
elapsed, and now we may draw the pieces of flesh out by means of the
thread and weigh them. The loss of weight, and consequently the amount
of flesh digested, is very different in the two cases. In that of the
dog without sham feeding the loss of weight amounts to merely 6 grams,
while the flesh withdrawn from the stomach of the other dog weighs only
70 grams, that is to say, was reduced by 30 grams. This, therefore,
represents the digestive value of the passage of food through the
mouth, the value of an eager desire for food, the value of an appetite.
I give also a series of figures obtained by Dr. Lobassoff in analogous
experiments. Into the dog’s stomach 25 pieces of flesh (100 grams)
were brought. The flesh remained two hours in the cavity. Without sham
feeding 6.5 per cent, with eight minutes' sham feeding 31.6 per cent,
of the quantity was digested.
Again: the flesh remained an hour and a half in the stomach; without
sham feeding 5.6 per cent, with five minutes' sham feeding 15 per cent,
was digested.
Once more: the flesh remained five hours in the stomach; without sham
feeding 58 per cent, with sham feeding 85 per cent, was digested, the
balance of undigested food being 42 per cent in the one case and 15 per
cent in the other.
I must, however, add that from the nature of this experiment it is not
well adapted for class demonstration, and may often fail. On the one
hand, it is not at all easy to conceal the introduction of the flesh
from the dog; on the other, the unusual and distracting surroundings
of the animal often causes a short period of sham feeding to have less
effect than would otherwise pertain. In order to avoid such failures
it is better before an audience to carry out this experiment only
on dogs accustomed to appear in the lecture theatre, and of whose
temperament the experimenter is well assured.
I hope you have now been convinced of the great importance which is to
be attached to the passage of food through the mouth and œsophagus, or,
in other words--and this, according to our former experiences, means
the same thing--to the eager desire for food. Without this longing,
without the assistance of appetite, many forms of food-stuffs which
gain entry to the stomach remain wholly devoid of gastric juice.
Others, it is true, excite a secretion, but the juice poured out is
scanty and weak.
It is only later, when we have still more fully recognised the
conditions upon which the secretory work of the gastric glands depends,
that we shall be able to grasp the meaning of these facts in a more
comprehensive manner. For instance, why does bread brought unnoticed
into the stomach of the dog cause no secretion for hours, while flesh
tolerably soon (after twenty to forty minutes) provokes this act? This
will be explained in the next lecture; now, however, we must consider
other questions.
How long does the after-effect, the echo of the first impulse to the
secretory nerves of the stomach, continue to last? How long does
appetite juice continue to flow after the normal act of eating, which,
especially in the case of animals, is not of long duration? We have
already determined many times, not only on our dog with the isolated
stomach, but also on other animals, how long the after-effect of sham
feeding is continued.
Here, for example, is an experiment from the article of Professor
Ssanozki which deals with the point. The dog had a gastric fistula and
also an opening leading into the œsophagus. After a sham feeding of
five minutes the secretion began, and was continued as follows:
Time in minutes. Quantity. Digestive power.
10 25.5 c.c. 8.1 mm.
10 20.0 ” 8.0 ”
10 13.5 ” 6.8 ”
10 11.0 ” 7.5 ”
10 8.5 ” 8.1 ”
10 6.5 ” 9.0 ”
20 13.5 ” 7.4 ”
20 11.0 ” 7.2 ”
20 7.0 ” 7.2 ”
20 11.5 ” 6.8 ”
20 11.0 ” 6.5 ”
30 6.5 ” 7.6 ”
20 5.5 ” 7.2 ”
The effect, therefore, even after a short period of sham feeding,
stretches over a length of time. Naturally the same holds good for the
taking of food in the normal way. One must, however, bear in mind that
in sham feeding, with all the force and reality of a hunger sensation
not satisfied, the eager desire for food, the effective agency, becomes
more and more accentuated, and therefore the secretory influence is
prolonged and more powerful. In normal feeding, however, the quelling
of the longing, the feeling of satisfaction which, as is well known,
sets in long before the termination of the digestive period from the
mere filling and distension of the stomach, must diminish the desire
for food, and, consequently, bring the secretory effect to an end.
It is, therefore, improbable that the whole secretory process in the
stomach, which, in the case of certain kinds and quantities of food,
lasts from ten to twelve hours, is dependent on the factors which we
have up to the present investigated. This is all the more obvious
since a sham feeding of five minutes, even under the most favourable
circumstances, does not call forth a secretion for longer than three to
four hours. We must, therefore, seek for other exciting agencies of the
innervation apparatus of the gastric glands.
Why and wherefore is the secretion instituted by psychic influence
maintained? What would first occur to all your minds is naturally
the immediate influence which the food exerts upon the walls of the
stomach. And this is true, but it does not happen in the simple, direct
fashion current in the minds of many physiologists and physicians. When
I said that bread or boiled white of egg, introduced directly into the
stomach, may not for hours produce a trace of secretion, probably many
of my hearers may have asked themselves with natural astonishment,
“How, then, is the effect of the forced feeding of phthisical and
insane patients, and the artificial feeding of those with gastric
fistulæ (performed on account of stricture of the œsophagus) to
be explained?” I will introduce my answer by a very unexpected
pronouncement relative to the assertion that mechanical stimulation of
the stomach wall by food constitutes a reliable and effective means
of calling forth the secretory work of the glands. This assertion,
which is so categorically set forth in many text-books of physiology,
and which consequently has gained hold of the mind of the physician,
is nothing else than a sad misconception degenerated into a stubborn
prejudice. My own statement, repeated in many published articles, and
at the meetings of various medical societies, that this dictum is only
a picture of the imagination, has met, for the most part, either with
an unbelieving shake of the head or else with a direct avowal that “it
cannot be so.” I regret exceedingly that these steadfast unbelievers
are not here, so that we might together bring the matter before the
tribunal of fact, to the demonstration of which we will now proceed. To
this matter I attribute very great importance. It is on this ground,
according to my opinion, that the whole battle must be fought out
between the generally accepted view that every agency is capable of
exciting the gastric mucous membrane and the theory that it is only
excitable by specific and selected stimuli. If once the defenders of
the old opinion are driven from their position and obliged to admit
the inefficiency of mechanical stimulation, there would be nothing
further left for them than to build up new theories and search out
old facts concerning gland work which have hitherto been rigidly kept
in the shade. We may take it that it is mainly because people were so
seized with the belief in the direct and simple mechanical explanation
that Bidder and Schmidt’s experiment of the excitation of gastric
secretion by mental effect has been so little taken into consideration,
notwithstanding that it appeared so thoroughly reliable and convincing.
I will now repeat the experiment of mechanical stimulation of the
gastric mucous membrane before you in the well-known, traditional,
and classic manner. Here is a dog with a gastric fistula on which
a cervical œsophagotomy has in addition been performed. I open the
fistula; as you see, nothing flows out of the stomach; it was washed
out clean with water an hour ago. We take the celebrated feather and
also a tolerably strong glass rod. Folds of blotting-paper saturated
with red and blue tincture of litmus are placed at hand. I now ask my
assistant to continuously move the feather and glass rod, alternately,
in all possible directions in the stomach, changing from one to the
other every five minutes. On removal from the stomach each is carefully
dried with red and blue blotting-paper. You have all seen, gentlemen,
that this procedure has now been kept up for half an hour. From the
fistular orifice not even a single drop has escaped, and, moreover, the
drops of moisture on all the pieces of red blotting-paper I have been
able to hand to you have assumed a distinct blue tinge, caused by the
moisture of the alkaline mucous membrane. The blue pieces, however,
have merely been made wet without altering their colour. Consequently,
with the most thorough mechanical stimulation of the whole cavity of
the stomach, we have not been able to find a single spot possessing a
noticeable acid reaction. Where, then, are the streams of pure gastric
juice of which we read in text-books! What objection can be raised
against the conclusiveness of this experiment? In my opinion only one:
that we are dealing with a dog out of health, whose gastric glands from
some possible cause are unable to react normally. This single objection
can be set aside before your eyes. After failing with the mechanical
stimulation, we proceed forthwith to the sham feeding of the same
animal. The dog takes the food offered it with keen appetite, and you
see that, exactly five minutes after beginning the feeding, the first
drops of juice appear from the stomach, followed by others faster and
faster. I catch a couple of drops on the blue litmus paper, and you see
that they produce bright red specks on the blue sheet. After thirty
minutes' sham feeding we have collected 150 c.c. of juice, which,
without filtering, looks as clear and transparent as water.
We cannot, therefore, possibly doubt that, when the proper stimulus is
used, the gastric glands react to it in a perfectly normal fashion,
furnishing a healthy gastric juice. From this it irrefutably follows
that only one explanation is to be found for the negative result in
the first half of our experiment, viz., that the mucous membrane
of the stomach, so far as secretory activity goes, is perfectly
indifferent to mechanical excitation. And yet this mechanical stimulus
is demonstrated as an exciting agency in the physiological lecture
theatre. I venture to think that this lecture experiment from now
onwards will quit the field, and give place to the one I have just
shown you. This apparently simple experiment of mechanical stimulation
can, however, only be successfully performed when certain very obvious
rules are followed. These, however, physiologists have not observed,
probably on account of a preconceived belief in the effectiveness of
the mechanical stimulus. These rules are two. First, it is necessary
that the stomach should be clean, and that nothing shall gain entry
to it from without. Such conditions were not formerly fulfilled. It
is true the stomach was emptied by removing the stopper from the
fistular cannula, but it was not washed out till an acid reaction
was no longer given, and consequently preformed gastric juice was
left behind between the folds of the mucous membrane. At the same
time saliva from the cavity of the mouth could gain entry, which
quickly became acidified in the incompletely emptied and imperfectly
washed-out organ. It is, therefore, not surprising that the glass
tube, by setting up contractions of the stomach, was the means of
expressing small quantities of acid fluid from the fistula-tube. (The
relationship between mechanical stimulation and the motor functions
of the stomach is not to be confounded with what we are here speaking
of.) That matters are as I state, and that the facts correspond to
the explanation is proved by this; namely, that nobody till now
has obtained genuinely pure gastric juice of an acidity amounting
to 0.5 or 0.6 per cent. It is only necessary to call to mind that
Heidenhain, when determining the acidity of the juice first obtained
from the resected stomach, was placed in no little doubt as to whether
his results (0.5 to 0.6) were correct, and his assistant at the
time (Gscheidlen) was set to verify the correctness of his standard
solutions. The acidity of the “purest” juice known at that time was
scarcely 0.3 per cent. As a further proof that none of the older
observers ever really obtained a secretion from mechanical stimulation
pure and simple, we may adduce the fact that none of them made mention
of the constant and precise period of five minutes' latency. To
overlook this was not possible if a genuine excitation of the glands
had been obtained.
Of no less importance is the second condition when we wish to perform
the experiment of mechanical stimulation in the correct way. It is
very necessary that the gastric glands be not already in activity at
the beginning of the experiment, and also that during the experiment
no impulse comes into play, which of itself, apart from mechanical
excitation, could excite the glands to secretion. Nor have we any
proof that observers formerly waited for hours before commencing
the experiment and convinced themselves that the gastric glands had
ceased working. On the contrary, we have not the slightest evidence to
indicate that the authors had attempted to guard against accidental
psychical stimulation of the glands--a matter which we have seen is of
considerable difficulty. And some dogs are so easily excited in this
way that it is almost impossible to bring their glands to rest, or at
least it is necessary to wait for hours. The experimenter must strain
his whole attention to preserve such an experiment free from objection.
It is only necessary that some food be near the dog, or that the hands
of the attendant who has prepared the food should smell of it, or that
some other similar circumstance should come into play, and the glass
tube, quite undeservedly, will be made answerable for the excitation of
the gastric glands. As you have just seen, both of our conditions have
been fulfilled on the dog before you, and the result of the experiment
stands in irreconcilable contradiction to those of the laboratory and
lecture experiment of former times.
The importance of the experiment, which I have already dwelt upon,
justifies me in making still further demands upon your attention in
order to show you two modifications of it. Nobody has as yet said, with
regard to mechanical stimulation, that in order to obtain results the
mechanical agency must simultaneously come into contact with numerous
points of the inner surface of the stomach. But in order to meet this
possible objection I will now show you two new modifications. Again
a similar dog is used, that is to say, one on which both gastrotomy
and œsophagotomy have been performed. The stomach has been washed out
clean and is at present in a state of complete rest. Into the fistula
I bring a thick glass tube containing a number of small openings (2
to 3 mm. diameter) at its rounded end. The other end of the tube is
connected with a glass ball containing tolerably coarse sand. Leading
into the ball is a second tube, with which an india-rubber pump can be
connected and a blast of sand blown through. By rhythmic compression
of the india-rubber ball I inject sand with considerable force into
the stomach, and this play is kept up for ten to fifteen minutes;
nevertheless, we see no trace of gastric juice. The sand falls out
again between the side of the cannula and the glass tube, and it
is either dry or scarcely moistened, but in no case is it able to
turn blue litmus red. And yet we are here dealing with a strong and
widely diffused stimulus. Look for a moment at the performance of the
bellows outside the stomach. From every opening of the tube--numbering
considerably more than ten--a strong stream of sand is ejected. If you
hold your hand against it, you feel quite distinctly that the grains
of sand strike with considerable force. And now, when our experiment
is ended, we may convince ourselves by sham feeding, in easy and
unquestionable fashion, that the innervation of the dog’s stomach is
perfectly normal.
Yet another experiment on a similar dog. Into its empty and resting
stomach an india-rubber ball is introduced. This is distended with
air by means of a syringe till it is as large as a child’s head and
maintained in this condition for a time, afterwards being allowed
to collapse. The procedure is kept up for ten to fifteen minutes.
During this time not a single drop of juice has appeared from the
stomach. The surface of the ball taken out of the organ is everywhere
alkaline. And here also subsequent sham feeding shows that the dog is
in a suitable condition for the experiment. I must add that in making
this observation the dog must not be too hungry, that is to say, must
have been fed within ten to twelve hours before, otherwise a psychic
excitation of the secretion can readily be induced.
If one dispassionately regards this question, and if any of our methods
for the study of gastric secretion are reliable, one must be convinced
step by step in the laboratory of the uselessness of mechanical
stimulation. In the case of dogs with an ordinary gastric fistula, and
failing some special reason, not a drop of gastric juice ever escapes
from the stomach other than during the digestive period. How could
this be the case if the mechanical stimulus were effective, since the
inner rim of the fistula-tube is continuously in contact with the
gastric mucous membrane? The same holds good for the dog with resected
stomach. During the experiment a glass or india-rubber tube is brought
sufficiently far into the _cul-de-sac_ to catch the juice, and yet not
a drop flows through the tube, nor does its inner surface ever become
acid, so long as true secretory conditions are absent. Moreover, the
tube has tolerably often to be taken out and set right.
In the ordinary gastric fistula in dogs, when the operation has lasted
a long time--over a year--folds of mucous membrane are often formed
in the neighbourhood of its inner orifice which completely close the
tube. In these cases a long, thick, perforated metal tube has to be
passed in deeply, and yet the manipulation of itself never calls forth
a secretion. Further, it is a daily occurrence to find in the stomach
of the dog thick rolls of hair, and yet their presence in no way
hinders the arrest of the secretion, which occurs when digestion has
ceased. Such an occurrence would have been specially obvious in our dog
with the isolated stomach, since it was bedded with sawdust in order
to guard against maceration of the wound by juice trickling out. Very
often we found enormous quantities of sawdust in the stomach, as much
as half a pound weight; obviously the dog had licked the wound from
adherent sawdust, which it then swallowed, together with that sticking
to its nose. And yet these particles of sawdust of themselves, which
certainly acted as mechanical stimuli, never caused a secretion. It
appears to me that this long series of facts ought to suffice to carry
the supposition to its grave that by direct mechanical stimulation
one is able to set the neuro-secretory apparatus of the stomach into
activity.
And yet the feather and the glass tube continue the even tenor of
their ways to this moment and function in some text-books, yea, even
in articles which specially treat of gastric secretion as exciters of
the gastric glands. There are, it is true, a few physiologists who
hold mechanical stimulation, in relation to gastric secretion, not to
be very effective, and give it a subordinate position in the series of
exciting agencies, but as yet I know of no other physiologist who has
wholly denied its influence, and who has not held it possible to obtain
at least some juice by it.
To conclude this lecture, we will take into consideration a question
connected with the matter we have just discussed. Since the contact of
food with the gastric mucous membrane has no direct influence on the
secretion, is its entry into the stomach devoid of all connection with
the secretory process?
It can hardly be doubted that, under normal conditions, the stomach is
the seat of certain definite sensations, that is to say, its surface
has a certain degree of tactile sensibility. This sensation is, as a
rule, very weak, and the majority of people become accustomed to pay
no heed to it in the normal course of digestion. They obtain their
sensations of general well-being, and especially of satisfaction
from the enjoyment of food, without taking cognisance of the factors
contributing to them. The feeling of general hunger, however, is
referred solely to the stomach.
On the other hand, all of us have met with men who could describe
exactly, and with gusto, how they were able to follow a special
tit-bit, or a mouthful of a favourite wine, the whole way through the
œsophagus down to the stomach, especially when the latter happened
to be empty. Naturally the gourmand, who directs his attention
continuously to the act of eating, can in the end distinctly perceive
sensations, and even call them up to the consciousness, which in other
people are normally masked by other sensations and impressions. We may
therefore take it that the satisfaction derived from eating is caused
not only by stimulation of the mouth and throat, but also by impulses
awakened by the passage of the food along the deeper portions of the
œsophagus and by its entry into the stomach. In other words, food which
merely passes through the mouth and throat produces less enjoyment
and excites, therefore, a less feeling of appetite than the food
which passes the whole way into the stomach. The appetite, the eager
craving after food, is, indeed, a very complex sensation, and often
not merely the need of the organism for food material is necessary for
its excitement, but also a condition of thorough well-being, together
with a normal healthy feeling in all parts of the digestive tract. For
this reason it is easy to understand how patients who have diseased
sensations in these organs, and who have no feeling of appetite,
no desire for food, remember the sensations, whether consciously or
unconsciously, even when they are no longer present. Cases are known
to neuro-pathologists where people with gastric anæsthesia suffered
from this loss of appetite. Such patients are no longer conscious of
having stomachs, and dislike the idea of eating because the food, as
they express it, appears to fall into a strange empty sack. In this
way one can also conceive how the appetite becomes lost in cases of
long-continued obstruction of the alimentary tube. The patients forget
their stomachs, and in such instances direct introduction of food into
the organ, after an operation, may suddenly bring back the appetite.
As a further illustration, I may be permitted to give an instance from
my own personal experience. After an illness with which a transient but
high fever was associated, although otherwise fully recovered, I had
lost all desire for food. There was something curious in this complete
indifference towards eating. Perfectly well, I only differed from
others in that I could with ease abstain from all food. Fearing that I
should collapse, I resolved on the second or third day to endeavour to
create an appetite by swallowing a mouthful of wine. I felt it quite
distinctly pass along the œsophagus into the stomach, and literally at
that moment perceived the onset of a strong appetite. This observation
teaches that the tactile sensation of the stomach at the moment of
entry of food is capable of awakening or increasing the appetite. It is
known that withholding food from the organism, or in other words the
creation of a necessity for food, does not lead immediately, nor in
all cases, to the production of an appetite, to a passionate craving
for food. How often does it happen that the ordinary hour for a meal
has struck, and yet, owing to some keenly interesting occupation, not
the least desire for food is felt? It is known to everybody, indeed it
has become a proverb, that real appetite first sets in with eating.
If this be true, the initial impulse towards awakening an appetite
may originate in the stomach and not in the buccal cavity. When we
spoke above of the desire for food being the excitant of the secretory
nerves of the stomach, we naturally meant the passionate and conscious
longing for food, that which is called “appetite,” and not the latent
need of the organism for nourishment, the lack of nutrition, which
has not yet been transformed into a concrete passionate desire. A
good example which enables us to differentiate between these two
factors is furnished by our dogs with sham feeding. The necessity for
food exists in such cases even before the experiment; the juice,
however, only begins to flow as soon as this need has taken the form
of a passionate longing. It is therefore quite possible that in the
case of some dogs, and at a certain stage of hunger, the touching of
the gastric mucous membrane with any object at hand, its mechanical
excitation, its distension by the food mass, may give the impulse which
excites the appetite, and when the appetite is awakened the juice
flows. This is possibly a third reason why, in the old experiment,
the mechanical stimulus came to be considered effective. Viewed from
this point it may, to a certain degree, lead to a reconciliation
between my assertion concerning the inefficiency of the mechanical
stimulus and the generally prevailing belief. I further also admit that
mechanical excitation will at times call into play the work of the
gastric glands, not however directly by means of a simple physiological
reflex, but indirectly, after it has first awakened and enlivened the
idea of food in the dog’s consciousness, and thereby called forth the
passionate desire. I hope that the foregoing will in no way lead to a
confusion of ideas in your minds, but will assist you to an exact and
concrete analysis of the previous simple explanation of the facts. This
representation, which bears more or less of a hypothetical character,
could, of course, be submitted to experimental proof. For such it is
only necessary to compare the influence which sham feeding exercises
in an œsophagotomised dog with that in one having a simple gastric
fistula.
LECTURE VIII
PHYSIOLOGICAL ACTION AND THE TEACHING OF INSTINCT: EXPERIENCES OF THE
PHYSICIAN
It would be desirable, in the interests of medicine, that the methods
described in these lectures should be employed in experimental
investigations into the pathology and therapeutics of the digestive
canal on the lines laid down--The fact that the beginning of the
secretory work in the stomach depends upon a psychic effect harmonises
with the experiences of every-day life, namely, that food should
be eaten with attention and relish--To restore the appetite has
from all ages been the endeavour of the physician--The indifference
of the present-day physician towards appetite--Probable causes of
this--Curative remedies based upon a restoration of appetite--The
therapeutic effects of bitters depend upon the excitation of
appetite--The usages of the mid-day meal are in agreement with
physiological requirements--Physiological reasons for certain
instinctive customs and empirical regulations--Importance of an
acid reaction of the food--Dietetics of fat and its therapeutic
application--The peculiar position of milk among food-stuffs is
based on physiological reasons--Explanation of the curative effects
of sodium bicarbonate and sodium chloride--The causes of individual
differences in the work of the digestive glands--Participation of
the inhibitory nerves of secretion in the production of pathological
effects.
GENTLEMEN,--To-day we shall endeavour to bring the previously
communicated results of our laboratory investigations into
reconciliation with the customs observed in the ingestion of food,
and with the regulations prescribed by the physician in disorders of
the digestive apparatus. To bring our knowledge to full fruition, and
so secure for it the most useful application, the same methods should
be applied from the same standpoint to the experimental investigation
of the pathology and therapeutics of the alimentary canal. Nor should
we be likely to encounter insuperable difficulties. Thanks to the
advances of bacteriology, many of the pathological processes can now
be experimentally produced in the laboratory. Moreover, we would,
in a sense, have to deal with external ailments, since our present
methods enable us to obtain access to any desired part of the inner
surface of the digestive canal. In such pathological animals the
functional diseases of the apparatus could be studied in a precise
and detailed manner; that is to say, the alterations of secretory
activity, the properties of the fluids, and the conditions under which
they appear could be examined. On such animals therapeutic remedies
could also be tested, the whole process of healing and the final result
experimentally observed, while the conditions of secretory activity
during every phase of the healing process could be investigated. It can
hardly be doubted that scientific, that is to say ideal, medicine,
can only take its proper position as a science when, in addition to an
Experimental Physiology and Pathology, there has also been built up an
Experimental Therapeutics. A proof that this is possible is furnished
by the recent vigorous strides made by the science of bacteriology.
I have already described one of such pathological therapeutic
experiments; namely, on the dog whose vagi nerves were divided in the
neck. Other similar cases I can also call to mind. Our dog with the
two stomachs suffered at one time from a slight and transitory gastric
catarrh. It was then very interesting to observe that the pathological
process (which we were usually able to wholly guard against) spread
from the large to the small stomach. It manifested itself here in
an almost continuous slimy secretion of very slight acidity, but of
strong digestive power. At the beginning of the ailment, indeed before
it became fully established, the psychic stimulation was remarkably
effective (that is to say, still furnished juice in appropriate
quantity), while local excitants almost completely failed. One may
conceive that the deeper layers of the mucous membrane with the gastric
glands were still healthy, and thus easily thrown into activity by
central impulses, whilst the surface of the membrane with the end
apparatus of the centripetal nerves was already distinctly damaged.
I mention these, which I may call impressions rather than precise
observations, because I wish to point out what a fruitful field awaits
the investigator who wishes to study, with the aid of our present
methods, the pathological conditions of the digestive organs and their
treatment. Such an investigation is all the more desirable because
clinical study of the same subject (notwithstanding the zeal devoted to
it during the last ten years and the results derived therefrom) has to
contend with serious difficulties. We must not forget that the sound or
stomach-tube, the chief clinical instrument, is more uncomfortable than
the ordinary form of gastric fistula which was previously practised on
animals, and yet the physiology of the stomach, even with the aid of
the latter, made no material progress for many long years. Nor is this
difficult to understand. The investigator obtained through the fistula
a mixture of substances from which it was difficult, or even at times
impossible, to decide anything.
Hence the exact scientific study of therapeutic questions in this
region still belongs to the future. But this does not exclude the
probability that the newer acquirements of physiology may fruitfully
influence the work of the physician. But physiology naturally can make
no pretence to guide the field of medicine, since the knowledge at its
disposal is incomplete and is much more restricted than that of the
broad world of clinical reality. As a recompense for this, however,
physiological knowledge is often able to explain the causation of an
illness and the meaning of empirical curative methods. To employ a
remedy the mode of action of which is not clear is quite a different
thing from knowing precisely what we are doing. In the latter case
the treatment of the diseased organ will be more effective because it
will be better adapted to the special needs of the case. It is thus
that medicine, being daily enriched by new physiological facts, will
at length grow into what it ideally must become; namely, the art of
repairing the damaged machinery of the human body, based upon _exact_
knowledge, or, in other words, applied physiology.
We may now return to our subject. If it be at all admitted that human
instinct is the outcome of an every-day experience, which has led to
the unconscious adoption of the most favourable conditions for life,
it is particularly so with regard to the phenomena of digestion. The
expression that physiology merely confirms the precepts of instinct
is justified here more than anywhere else. It appears to me also
that, in relation to the foregoing facts, instinct has often made
out a brilliant case when brought before the tribunal of physiology.
Perhaps the old and empirical requirement, that food should be eaten
with interest and enjoyment, is the most imperatively emphasised and
strengthened of all. In every land the act of eating is connected
with certain customs designed to distract from the business of daily
life. A suitable time of day is chosen, a company of relatives,
acquaintances, or comrades assemble. Certain preparations are carried
out (in England a change of raiment is usually effected, and often a
blessing is asked upon the meal by the oldest of the family). In the
case of the well-to-do a special room for meals is set apart, musical
and other guests are invited to while away the time at meals--in a
word, everything is directed to take away the thoughts from the cares
of daily life, and to concentrate them on the repast. From this point
of view it is also plain why heated discussions and serious readings
are held to be unsuitable during meal-times. Probably this also
explains the use of alcoholic beverages at meals, for alcohol, even
in the lighter phases of its action, induces a mild narcosis, which
contributes towards distraction from the pressing burden of the daily
work. Naturally this highly developed hygiene of eating is only found
in the intelligent and well-to-do classes, first, because here the
mental activity is more strained and the various questions of life more
burning; and secondly, because here also the food is served in greater
quantity than is required for the wants of the organism. In the case of
the poorer classes, where mental activity is less highly developed, the
greater amount of muscular activity and the constant lack of more than
sufficient nourishment insure a strong and lively desire for food in a
normal manner, without recourse to any special regulations or customs.
The same conditions explain why the preparation of food is so choice
in the case of the upper classes and so simple in that of the lower.
Further, all the accessories of the meal, which are foretastes of the
actual repast, are obviously designed to awaken the curiosity and
interest, and to augment the desire for food. How often do we see that
a person who begins his customary meal with indifference afterwards
enjoys it with obvious pleasure when his taste has been awakened by
something piquant or, as we say, appetising. It was here only necessary
to give an impulse to the organs of taste, that is, to excite them, in
order that their activity might be later maintained by less powerful
excitants, for a person who feels hungry such extra inducements are,
of course, not necessary. The quelling of hunger in his case affords of
itself sufficient enjoyment. It is not, therefore, without reason that
it is often said that “Hunger is the best sauce.” This dictum, however,
is only right up to a certain point, for some degree of appetising
taste is desired by everybody, even by animals. Thus, a dog which has
not fasted for more than some hours will not eat everything with equal
pleasure which dogs usually eat, but will seek out the food which it
relishes best. Hence the presence of a certain kind of spice is a
general requirement, although naturally individual tastes differ.
This short discussion as to how different people behave with regard
to the act of eating is of itself testimony that care should ever be
taken to keep alive the attention and interest for food and to promote
enjoyment of the repast--that is to say, that care should be taken of
the appetite. Every one knows that a normal, useful food is a food
eaten with appetite, with perceptible enjoyment. Every other form of
eating, eating to order or from conviction, soon becomes worse than
useless, and the instinct strives against it. One of the most frequent
requests addressed to the physician is to restore the appetite. Medical
men of all times and of every land have held it to be a pressing
duty, after overcoming the fundamental illnesses of their patients, to
pay special attention to the restoration of the appetite. I believe
that in this they are not only animated by an endeavour to free their
patients from troublesome symptoms, but also by the conviction that
the return of appetite of itself will favour the restitution of normal
digestive conditions. It may be said that to the same extent to which
the patient wishes back his appetite the physician has effectively
employed measures to restore it. Hence we have not a few remedies which
are specially named “gastric tonics,” and whose action is to promote
appetite. Unfortunately medical science has latterly deviated from
this, the correct treatment of the appetite, and that which corresponds
to the real conditions. If one reads current text-books on disorders of
digestion, it is remarkable how little attention is paid to appetite
as a symptom or to its special therapy. Only in a few of them is its
importance indicated, and then merely in short, parenthetic phrases.
On the other hand, one may meet statements in which the physician is
recommended to adopt no special means for counteracting so unimportant
a subjective symptom as a bad appetite! After what I have said and
demonstrated to you in these lectures, one can only designate such
views as gross misconceptions. If anywhere, it is precisely here
that symptomatic treatment is essential. When the physician finds it
necessary, in disorders of digestion, to promote secretory activity by
different remedies, this object can most certainly and completely be
achieved by endeavouring to restore the appetite. We have already seen
that no other excitant of gastric secretion, so far as quantity and
quality of the juice are concerned, can compare with the passionate
craving for food.
To a certain degree we can understand--and this contributes to an
explanation of matters--how medical science of our time has come
to regard so lightly the loss of appetite as a special object for
treatment. Now, however, the experimental method has penetrated more
and more into medical science, with the result that many pathological
factors and therapeutic agents are judged of according to whether they
hold good in the laboratory or not--that is to say, they are valued
only in so far as they can be verified by laboratory experiments.
Naturally we do not doubt that a movement in this direction indicates
a great advance, but even here, as with every undertaking of mankind,
things do not proceed without mistakes and exaggerations. We must not
consider an event to be a mere picture of the imagination because
it is not realisable under given experimental conditions. We often
do not know all the essential conditions for the production of the
phenomenon in question, nor are we yet able to grasp the connection
between all the separate functions of life as fully as may be desired.
Thus in the clinical treatment and pathology of digestion assistance
was sought for in the laboratory, but nothing was there met with which
had a relation to appetite, and consequently this factor was overlooked
in medical practice. As stated above, the psychic gastric juice
obtained only cursory mention in physiology, and this not even by all
authors; and when it was noticed it was related more as a curiosity.
Great importance was, on the other hand, assigned to the mechanical
stimulus, the efficiency of which, now that our knowledge is more
complete, has been shown to be purely imaginary. Each of the contending
factors has at length been assigned its proper place, and if clinical
medicine maintains her worthy desire of following out the experimental
investigation of her problems, she must in actual practice accord to
appetite its old claim for consideration and treatment.
But notwithstanding the indifference of physicians to appetite in
itself, many therapeutic measures are based on the promotion of it.
And in this the truth of empiricism makes itself irresistibly felt.
When the patient is enjoined to eat sparingly, or when he is restrained
from eating at all till the physician expressly permits, or again, when
he is (for instance, during convalescence) removed from his ordinary
surroundings and sent to an establishment where the whole life, and
particularly the eating, is regulated according to physiological
needs--in all these cases the physician seeks to awaken appetite, and
relies upon it as a factor in the cure. In the first case, where the
food is prescribed in small portions, in addition to preventing the
overfilling of a weak stomach, the oft-recurrence of appetite juice,
which is so rich in quantity and so strong in digestive power, is of
great importance. I ask you here to call to mind one of our experiments
in which food was given in small portions to a dog, and thus led to
a secretion of much stronger juice than if the whole ration had been
eaten at once. This was an exact experimental reproduction of the
customary treatment of a weak stomach. And such a regulation of diet
is all the more necessary, since, in the commonest disorders of the
stomach, only the surface layers of the mucous membrane are affected.
It may, consequently, happen that the sensory surface of the stomach,
which should take up the stimulus of the chemical excitant, is not
able to fulfil its duty, and the period of chemical secretion, which
ordinarily lasts for a long time, is for the most part disturbed, or
even wholly absent. A strong psychic excitation, a keen feeling of
appetite, may evoke the secretory impulse in the central nervous system
and send it unhindered to the glands which lie in the deeper as yet
unaffected layers of the mucous membrane.
An instance of this, taken from the pathological material of the
laboratory, I have already related at the beginning of this lecture. It
is obvious in these cases that the indication is to promote digestion
by exciting a flow of appetite juice, and not to rely upon that excited
by chemical stimuli. From this point of view the meaning of removing
a patient, the subject of chronic weakness of the stomach, from his
customary surroundings is also plain. Take, for instance, a mentally
overstrained individual, or a responsible official; how often does
it happen that he cannot for a moment distract his thoughts from his
daily work. He eats without noticing it, or eats and carries on his
work at the same time. This often happens, particularly in the case of
people who live in the midst of the incessant turmoil of great cities.
The systematic inattention to the act of eating prepares the way for
digestive disturbances in the near future, with all their consequences.
There is no appetite juice, no “igniting juice,” or, at most, very
little. The secretory activity comes slowly into play; the food remains
much longer in the digestive canal than is necessary, or passes, for
want of sufficient digestive juices, into a state of decomposition
which irritates the mucous membrane of the alimentary canal and brings
it into a condition of disease. No medicinal treatment can help
such a patient while he remains surrounded by his old conditions.
The fundamental cause of his illness still continues in progress.
There is only one course to pursue; namely, to take him completely
away, to free him from his occupation, to interrupt the interminable
train of thought, and to substitute for a time, as his only object
in life, the care of his health, and a regard for what he eats. This
is attained by sending the patient to travel, or by placing him in a
hydropathic establishment. It is the duty of the physician to regulate
not only the life of individual patients according to such rules,
but also to have a care that in wider circles of the community a due
conception of the importance of eating should be disseminated. This
is particularly so with the Russian physician. It is precisely in the
so-called intelligent classes of Russians that a proper conception
of life generally is often found wanting, and where an absolutely
unphysiological indifference towards eating often exists. More
methodical nations, like the English, have made a species of cult of
the art of eating. It is, of course, degrading to indulge excessively
and exclusively in culinary enjoyments, but, on the other hand, a lofty
contempt for eating is also reprehensible. As so often is the case, the
best course here also lies between the two extremes.
With the establishment of mental effect upon the secretion of juice the
influence of condiments enters upon a new phase. The conclusion had
already been empirically arrived at that it was not alone sufficient
for the food to be composed exclusively of nutrient substances, but
that it should also be tasty. Now, however, we know why this is so.
For this reason the physician, who has often to express an opinion
upon the suitability of the dietaries of different persons, or even
of whole communities, should constantly bear in mind the question of
psychic secretion; that is to say, he should inquire after and learn
how the food has been eaten, whether with or without enjoyment. But how
often do the people who have charge of the commissariat pay attention
solely to the nutritive value of the food, or place a higher value on
everything else than taste? We must, further, in the interest of the
public weal, direct attention especially to the feeding of children.
If this or that inclination of the taste ultimately determines the
relation of grown-up individuals towards food, a matter with which
the commencing phase of digestion is closely linked, it would seem
undesirable to habituate children solely to a nicety and uniformity of
gustatory sensations. Such might effect their capabilities of adapting
themselves to other conditions in after life.
The question of the therapeutic influence of the so-called bitters,
it appears to me, bears the closest connection with that of appetite.
After a long period of high repute these substances have been almost
expelled from the list of pharmaceutic remedies. When tested in
the laboratory, they were unable to justify their old and valued
reputation; when directly introduced into the stomach, many of them
were unable to produce a flow of gastric juice. Consequently, in the
eyes of the clinician, they became greatly discredited, so that many
were quite ready to discard their use altogether. Obviously, the simple
conclusion was drawn that a weak digestion could only be assisted by
a remedy which directly excites secretory activity. In this, however,
it was forgotten that the conditions of the experiment possibly had
not corresponded with the actual state of affairs. The whole question
of the therapeutic importance of the bitters, however, acquires a
different significance when we link it with another question, such, for
instance, as how do bitters affect the appetite? It is the universal
opinion of the earlier and later physicians that bitters increase
the appetite, and if this be so everything is said. They are, in
consequence, real secretory stimulants, since the appetite, as has many
times been repeated in these lectures, is the strongest of all stimuli
to the digestive glands. It is, however, not by any means strange
that this had not previously been observed in the laboratory. The
substances were either introduced directly into the stomachs of normal
dogs or else injected into the circulation. But their action is chiefly
bound up with their effect upon the gustatory nerves, and it was not,
therefore, without some reason that this large group of remedies,
consisting of substances of the most varied chemical composition, were
grouped together mainly on account of a certain bitter taste common
to them all. A person who suffers from digestive disturbance has,
moreover, a blunted taste, a certain degree of gustatory indifference.
The ordinary foods, which are agreeable to other people, and also to
himself when in health, now appear tasteless. They not only arouse no
desire for eating, but may even cause a feeling of dislike; there
is no sense of taste, or at best a perverse one. It is necessary,
therefore, that the gustatory apparatus should receive a strong
stimulus in order to restore a normal sensation. As experience teaches,
this object is most quickly attained by exciting sharp, unpleasant,
gustatory impressions, which by contrast awaken the idea of pleasant
ones. In either case there is no longer indifference, and this is the
foundation upon which an appetite for this or that kind of food may
be awakened, and here a general physiological law is illustrated. The
light appears brighter after darkness, a sound louder after silence,
the enjoyment of blithesome health more intense after illness, and so
on. This explanation of the appetising effects of bitters proceeding
from the mouth does not exclude the possibility of some such similar
influence coming also from the stomach. As has been already stated in
the fifth lecture, there is some reason for believing that certain
impulses from the cavity of the stomach are likewise necessary for
the excitation of appetite. It is possible that bitters not only act
directly on the gustatory nerves in the mouth, but that they also act
on the mucous membrane of the stomach in such a way that sensations
are generated which contribute to the passionate craving for food. As
a matter of fact, it has been confirmed by many clinicians that after
the administration of bitters some such special sensations do arise
in the stomach. The effect of these remedies consists, therefore, not
merely in the generation of a simple reflex, but in the production of
a certain psychic effect, which indirectly excites a physiological
secretory activity. The same probably applies to other substances, such
as condiments. In any case, whether our explanation corresponds to the
actuality or not, the question of the therapeutic effect of bitters
is settled in the affirmative the moment we acknowledge that these
substances awaken appetite. The problem, therefore, of an experimental
investigation of bitters consists in establishing the fact that they
have an effect upon the appetite. The question is a difficult one,
and has not hitherto been attempted in the laboratory. It is not
sufficient to hand over clinical observations to the laboratory as
experimental proofs. One must have, in addition, the assurance that the
investigation has been correctly carried out; that is to say, that it
dealt exactly with the point under consideration. It is interesting to
observe that the connection between appetite and gastric juice is by
many physicians, and in many text-books of medicine, exactly reversed.
Thus it is represented that some medicinal remedy calls forth a
secretion of gastric juice, and this, by its presence in the stomach,
awakens an appetite. Here we have to deal with a false explanation of
a true fact, and that because it was not recognised that a psychic
effect could by any possibility be a powerful excitant of secretory
nerves. The customs of the chief meal of the day also correspond with
our physiological results. After this or that _hors d’œuvre_, perhaps
also with a liqueur of brandy (especially customary in Russia), both of
which are designed to awaken the appetite, the repast proper begins,
and, in the majority of cases, with something hot, consisting mostly of
meat broth (_bouillon_, different soups, and so on). After this comes
the really nourishing food--meat of different kinds served in various
ways, or, in the case of poorer people, stews made with vegetables,
and therefore rich in carbohydrate material. This sequence of foods,
from the standpoint of physiology, is quite rational. Meat broth, as
we have already seen, is an important chemical excitant of gastric
secretion. An attempt is therefore made in two ways to secure a free
secretion of gastric juice to act on the chief food; first, in the
excitement of the appetite juice by the _hors d’œuvre_, and secondly,
in the promotion of the flow by the action of the meat broth. It is in
this way that human instinct has made provisions for the digestion of
the chief meal. A good meat broth can only be afforded by well-to-do
people, and consequently with the poorer classes a less expensive,
and, indeed, also a less effective, chemical excitant is used for
awakening the early secretion. For example, _kwas_[31] serves in this
way with the Russian population, while in Germany, where the price
of meat is high, different kinds of soups are used, consisting of
water mixed with flour, bread, etc. It is further to be borne in mind
that the quantity of the digestive juices in general stands in close
connection with the content of water in the organism. This has been
shown by the experiments of Dr. Walther for the pancreatic juice, and
by my own for the gastric juice. If this sequence of foods, therefore,
holds good for healthy people, it must be even more strictly adhered
to in pathological conditions. Thus, when a person has no appetite,
or only a weak one, he has no psychic juice or only very little;
consequently, the meal must in every case be begun with a strong
chemical excitant--for example, with a solution of the extractives of
flesh. Otherwise solid foods, particularly if they do not consist of
meat, would remain long in the stomach without any digestion whatever.
It is, therefore, in every way desirable to prescribe meat juice,
strong broth, or meat extract to people who have no appetite. The same
applies also to forced feeding, for instance, of the insane. It is true
that the method of introduction in this case necessarily secures the
presence of a chemical excitant, since the food can only be introduced
in a fluid form. In any case the addition of meat extract would be very
useful. If one arranged the ordinary fluid foods in descending order,
according to the influence of the chemical excitants, the following
would be the series: first, the preparations of the flesh, such as meat
juice and the like; secondly, milk; thirdly, water.
The usual termination of the repast is also, from the physiological
standpoint, easy to be understood. The chief meal is generally ended
with something sweet, and everybody knows that sweets are pleasant.
The meaning of this is easy to guess. The repast, begun with pleasure,
consequent on the pressing need for food, must also, notwithstanding
the stilling of hunger, be terminated with an agreeable sensation. At
the same time the digestive canal must not be burdened with work at
this stage; it is only the gustatory nerves which should be agreeably
excited. After thus dealing in general with the usual arrangement of
our meals, we may now speak of some special points.
Above all comes the acid reaction of the food. It is apparent that
acidity enjoys a special preference in the human taste. We use quite
a number of acid substances. Thus, for example, one of the commonest
seasoning substances is vinegar, which figures in a number of sauces
and such like. Further, many kinds of wine have a somewhat acid
taste. In Russia, _kwas_, especially in the acid form, is consumed in
great quantities. Moreover, acid fruits and green vegetables are used
as food, and they are either of themselves acid, or made so in the
preparation. In medicine this instinct is likewise often made use of,
and acid solutions, especially of hydrochloric and phosphoric acids,
are prescribed in digestive disturbances. Finally, Nature itself
constantly endeavours to prepare lactic acid in the stomach in addition
to the hydrochloric acid. The former arises from the food introduced,
and is consequently always present. These facts are all physiologically
comprehensible when we know that an acid reaction is not only necessary
for an efficient action of the peptic ferment, but is at the same time
the strongest excitant of the pancreatic gland. It is even conceivable
that in certain cases the whole digestion may depend upon the
stimulating properties of acids, since the pancreatic juice exerts a
ferment action upon all the constituents of the food. In this way acids
may either assist digestion in the stomach where too little gastric
juice is present, or bring about vicarious digestion by the pancreas
where it is wholly absent. It is easy, therefore, to understand why the
Russian peasant enjoys his _kwas_ with bread. The enormous quantity
of starch which he consumes, either as bread or porridge, demands a
greater activity upon the part of the pancreatic gland, and this is
directly brought about by the acid. Further, in certain affections of
the stomach, associated with loss of appetite, we make use of acids,
both from instinct as well as medical direction, the explanation being
that they excite an increased activity of the pancreatic gland, and
thus supplement the weak action of the stomach. It appears to me that a
knowledge of the special relations of acids to the pancreas ought to be
very useful in medicine, since it brings the gland--a digestive organ
at once so powerful and so difficult of access--under the control of
the physician. We could, for instance, intentionally discard digestion
in the stomach, and thus transfer it to the bowel, by prescribing
substances which do not excite the gastric glands. On the other hand,
by lessening the acidity of the gastric juice we could reduce the
activity of the pancreas, and these are matters which might be made use
of in various special diseases, or even in some general disturbances of
the digestive apparatus.
No less instructive is a comparison of the results of our experiments
upon fat, with the demands of instinct and also with the precepts of
dietetics and therapeutics. Everybody knows that fatty foods are heavy,
that is, difficult of digestion, and in the case of weak stomachs
they are usually avoided. We are now in a position to understand this
physiologically. The existence of fat in large quantities in the chyme
restrains in its own interest the further secretion of gastric juice,
and thus impedes the digestion of proteid substances; consequently, a
combination of fat and proteid-holding foods is particularly difficult
to digest, and can only be borne by those who have good stomachs
and keen appetites. The combination of bread and butter is less
difficult, as might _a priori_ be inferred from its wide employment.
Bread requires for itself, especially when calculated per unit, but
little gastric juice and but little acid, while the fat which excites
the pancreatic gland insures a rich production of ferment both for
itself and also for the starch and proteid of bread. Fat alone does
not count by any means as a heavy food, as may be seen from the fact
that large quantities of lard are consumed in certain districts of
Russia with impunity. This also is comprehensible, since the inhibitory
influence of the fat in this case does not prevent the digestion of
any other food-stuff, and is conducive to the assimilation of the
fat itself. There is no struggle in this case between the several
food constituents, and therefore no one of them suffers. In harmony
also with daily experience the physician, in cases of weakness of the
stomach, totally excludes fatty food and recommends meat of a fat-free
kind; for example, game, etc. In pathological cases, however, where an
excessive activity of the gastric glands is manifested, fatty food,
or fat as emulsion, is prescribed. And here medicine has empirically
brought to its aid the restraining action of fat, which we have so
strikingly seen in our experiments.
Amongst all the articles of human food, milk takes a special position,
and this is unanimously recognised, both in daily experience and in the
practice of medicine. By everybody milk is considered a light food,
and is given in cases of weak digestion as well as in a whole series
of severe illnesses; for example, in heart and kidney affections. The
extreme importance of this substance, a food prepared by Nature itself,
we can now well understand. There are three properties of milk which
secure it an exceptional position. As we already know, in comparison
with nitrogenous equivalents of other foods, the weakest gastric juice
and the smallest quantity of pancreatic fluid are poured out on milk;
consequently, the secretory activity requisite for its assimilation is
much less than with any other food-stuff. In addition, milk possesses
a further important property. Thus, when it is introduced unobserved
into the stomach of an animal it causes a secretion both in the stomach
and also one from the pancreas; consequently, it appears to be an
independent chemical excitant of the digestive canal; and in this
action it is remarkable that we perceive no essential difference in
the effect when the milk is brought unnoticed into the stomach from
that which occurs when it is given to the animal to lap. Although
flesh is a better chemical excitant, it is by no means a matter of
indifference how it gets into the stomach. It must, therefore, be
accepted that milk excites not only a really effective, but at the same
time a very economic, secretion, and also that the appetite is unable
to stimulate this secretion into a more active or abundant flow. The
secret of the relation of milk to the secretion of the digestive juices
can, unfortunately, at present be submitted to no further analysis or
investigation. We are at liberty, however, to suppose that the fat on
the one hand is of importance for the inhibition of the gastric glands,
and the alkalinity on the other for the restraint of the pancreas. Thus
the gastric glands and the pancreas, notwithstanding the presence of
excitants, are maintained by milk at a certain but not too high degree
of activity, a matter which is in every way desirable in consideration
of the easy digestibility of its constituents. Finally, the third
characteristic which is observed to belong to milk, and which is
probably only an expression of the first, consists in the following.
When one administers to an animal equivalent quantities of nitrogen, in
the one case as milk, in the other as bread, and afterwards estimates
the hourly output of nitrogen in the urine, it results that the
increase during the first seven to ten hours after the milk (compared
with the excretion beforehand) amounts only to from 12 per cent to 15
per cent of the nitrogen taken in, while after bread it amounts to 50
per cent. If the hourly rate of absorption and the extent to which
milk and bread are respectively used up be taken into consideration,
it has to be admitted that these augmentations of urinary nitrogen
which appear soon after feeding must be expressions of the functional
activity of the digestive canal itself, and that this activity in the
case of bread is three or four times greater than in the case of milk
(_Experiments of Prof. Rjasanzew_); consequently, in the case of milk
a much larger fraction of its nitrogen is free to be used up by the
organism at large (irrespective of the organs of digestion) than in
that of any other kind of food. In other words, the price which the
organism pays for the nitrogen of milk, in the form of work on the part
of its digestive apparatus, is much less than that for other foods. How
admirably, therefore, the food prepared by Nature distinguishes itself
when compared with all others!