OF THE FUNCTION OF EXCRETION.
In what excretion differs from secretion—Excretion in the
plant—Quantity excreted by the plant compared with that excreted
by the animal—Organs of excretion in the human body—Organization
of the skin—Excretory processes performed by it—Excretory
processes of the lungs—Analogous processes of the liver—Use of the
deposition of fat—Function of the kidneys—Function of the large
intestines—Compensating and vicarious actions—Reasons why excretory
processes are necessary—Adjustments.
844. The various matters contained in organized bodies, and even
those which enter as constituent elements into their composition, are
constantly removed from the system, and thrown off into the external
world. The matters thus rejected are called excretions; and the various
processes by which their elimination is effected constitute a common
function termed excretion.
845. Excretion is the necessary consequence of the deterioration which
all organized matter undergoes by the actions of life. The matters
removed by the process consist of the waste particles of the body, or
the particles expended in the vital actions, as the aliment contains
the particles which replenish the waste, and compensate the expenditure.
846. The excretions are separated from the common organized mass by
processes perfectly analogous to those comprehended in the great
function of secretion. Excretion is only a particular form of
secretion: the difference between the two functions is, that, in the
former, the matter eliminated being either noxious or useless, is
separated for the sole purpose of being rejected; while, in the latter,
the matter eliminated is destined to perform some useful purpose
in the economy. Accordingly, the products of excretion are termed
excrementitious; and those of secretion, recrementitious.
847. The chief matters excreted by the plant are oxygen, carbonic acid,
air; water, in some few cases, under peculiar circumstances, ammonia
and chlorine; and in still rarer cases, during the night, poisonous
substances, as carburetted hydrogen, together with acrid, and even
narcotic principles.
848. The forms under which these excretions are eliminated are
exceedingly various. Sometimes the matter excreted is in the shape of
gas, at other times it is in that of vapour, and at others in that of
liquid. The chief gaseous exhalations are oxygen and carbonic acid;
the vaporous exhalations consist principally of water, in the state
of vapour; and the liquid exhalations are either pure water, or water
holding in combination sugar, mucilage, and other proximate vegetable
principles. Even the peculiar products formed by the vital actions
of the plant, as the volatile oils, the fixed oils, the balsams, the
resins, and perhaps, with the exception of gum, sugar, starch, and
lignine, all the substances formed out of the proper juices of the
plant, are true excretions; for these substances are fixed immovably
in the cells, sacs, or tubes which secrete and contain them: they are
not consumed in the growth of the plant; they do not appear to be
applied to any useful purpose in the economy; they are injurious, and
even poisonous to the very plant in which they are formed when taken up
by the roots and combined with the sap: as long as they remain in the
plant they are isolated in the individual parts in which they are first
deposited, until with the advancing age of the plant they lose their
aqueous particles, and are finally dried up; they, therefore, possess
all the essential characters of excrementitious substances.
849. The organs by which these matters are excreted are the leaves, the
flowers, the fruits, the roots, and certain bodies called glands.
850. The gaseous and vaporous exhalations are effected chiefly by the
leaves, which it has been shown (320 and 465), under the influence of
the solar ray, are always pouring out a large quantity of oxygen, and
still larger quantities of fluid in the state of vapour.
851. Similar matters are exhaled by the flowers either in the form
of vapour or of liquid; and this exhalation commonly bears with it
a peculiar odour, which proceeds from an essential oil, sometimes
evaporated with the pollen, and at other times secreted by glandular
bodies which have their seat in the petals.
852. Fruits, and especially green fruits, as raspberries, pears,
apples, plums, apricots, figs, cherries, gooseberries, and grapes, pour
out oxygen during the day, and carbonic acid gas during the night, and
thus co-operate with leaves in carrying on the function of excretion.
853. The more elaborate excretions contained in special receptacles,
and formed by diverse organs from the proper juices of the plant,
descend chiefly by the bark, and are poured by the roots into the soil.
These excretions, if re-absorbed by the roots, and re-introduced into
the system of the plant that has rejected them, poison that plant.
Consequently, two processes of deterioration are always going on in the
soil; first, the absorption of the nutrient matter contained in it;
and, secondly, the accumulation of excrementitious matter constantly
poured into it by the growing plant. By the addition of manure, the
soil is replenished with fresh nutritive materials; by a rotation of
crops, it is purified from noxious excretions. It is a remarkable
and beautiful adjustment, that excrementitious substances which are
destructive to plants of one natural family, actually promote the
growth of plants of a different species. Thus, if wheat be sown upon
a tract of land proper for that grain, it may produce a good crop the
first, the second, and perhaps even the third year, as long as the
ground is what the farmers call in good heart. But, after a time, it
will yield no more of that particular kind of corn. Barley it may still
bear, and, after this, oats, and perhaps after these, pease, or some
other species belonging to a different family. The excrementitious
matter deposited in the soil by a preceding is absorbed by a succeeding
crop; the matter excreted by the former serving as nutriment or
stimulus to the latter. But though in this mode all noxious matter is
removed from the soil, yet the ground at last becomes quite barren, in
consequence of having parted with all its nutrient particles, and then
it will yield no more produce until it is supplied with a new fund of
matter. This new matter is afforded by vegetable or animal substances,
in which, the principle of life having become extinct, the peculiar
bond that held their particles together is dissolved. Leaves, flowers,
fruits, bark, roots; hair, skin, horns, hoofs, fat, muscle, bone, the
blood itself, whatever has formed a part of the organized body, now
dead, and repassing through the process of decomposition, back to the
simple physical elements, all its forms of beauty gone, and exhaling
only matters highly deleterious to animal life, mixed with the soil,
are recombined into new products, spring up into new plants, and thus
re-appear under new forms of beauty, and afford fresh nutriment to
myriads of animals. The very refuse of the matters which have served as
food and clothing to the inhabitants of the crowded city, and which,
allowed to accumulate there, taint the air, and render it pestilential,
promptly removed, and spread out on the surface of the surrounding
country, give it healthfulness, clothe it with verdure, and endow it
with inexhaustible fertility.
854. The quantity of matter excreted by the plant is proportionate to
the energy of its vital actions. Hence it is always greatest in spring,
when the tender leaves are beginning to shoot; gradually diminishes as
autumn approaches; and, at last, as the leaves turn yellow, and the
vessels which connect the leaves with the stalk dry up and are closed,
it almost wholly ceases.
855. It is copious in proportion to the number of the leaves, and to
the extent of the surface they present. From experiments performed as
long ago as the year 1699, by Woodward, it appears that, of the whole
quantity of water absorbed by the plant, the least proportion exhaled
to that retained is as 46 or 50 to 1; in many cases it is as 100 or 200
to 1, and in some above 700 to 1. In one experiment, a plant which
imbibed 2501 grains of water, increased in weight only three grains
and a half: hence the dampness and humidity of the air in all places
in which trees and the larger vegetables abound; more especially when
the leaves are young, and most numerous and active; and hence also the
magnitude of the rivers in all extensive countries which are covered
with forests.
856. Exhalation, scarcely appreciable in the night, is most abundant
during the day under the influence of the solar light. If two plants
of the same size are covered with two glass bells, and one be exposed
to the sun’s light, while the other is left in the shade, the inner
surface of the former bell becomes covered with drops of water, while
that of the second remains perfectly dry.
857. The absolute quantity of matter excreted by the plant is widely
different in different species. According to Hales, in a sun-flower
three feet and a half high, the leaves of which presented a surface
of 5616 square inches, or 39 square feet, the greatest quantity
exhaled in twelve hours, during the day, was one pound fourteen
ounces avoirdupois; the medium quantity one pound four ounces. In a
middle-sized cabbage, the greatest quantity exhaled was one pound
nine ounces; the medium quantity one pound three ounces. In a vine,
the greatest quantity exhaled was six ounces; the medium quantity
five ounces. In a young apple tree having 163 leaves, the surface
of which was equal to 1589 square inches, or 11 square feet, the
greatest quantity exhaled was eleven ounces; the medium quantity nine
ounces. Martino calculated the quantity exhaled by a cabbage, in the
twenty-four hours, at twenty-three ounces; by a young mulberry-tree,
eighteen ounces; and, by a maize plant, seven drachms.
858. Supposing the weight of the human body to be 160 pounds, and
the weight of a sun-flower 3 pounds, the relative weights of the two
bodies will be as 160 to 3, or as 53 to 1. The surface of such a human
body is equal to 15 square feet, or 2160 square inches; the surface
of the sun-flower is 5616 square inches, or as 26 to 10. The quantity
perspired in the twenty-four hours by an ordinary-sized man, according
to the estimate of Keill, is about thirty-one ounces. Allowing two
ounces for the exhalation during the beginning and the ending of
the night, the quantity exhaled by the plant, in the same time, is
twenty-two ounces; so that the perspiration of a man to that of a
sun-flower is nearly as 141 to 100, though the weight of the man to
that of the sun-flower is as 53 to 1. Taking bulk for bulk, the plant
imbibes seventeen times more fresh fluid than the man, partly, no
doubt, for the reason assigned by Hales—because, “the fluid which is
filtered through the roots of the plant is not near so full freighted
with nutrient particles as the chyle which enters the lacteals of the
animal; the plant, therefore, requires a much larger supply of fluid.”
859. As soon in the animal series as organs are formed distinct from
the homogeneous mass of which the minute and simple beings placed
at the bottom of the scale appear to consist, these organs are
appropriated, at least in part, to the function of excretion. In the
human being, six organs take a part, and are chiefly appropriated to
this function—namely, the skin, the lungs, the liver, the adipose
tissue, the kidneys, and the intestinal canal. All these organs serve
other purposes in the economy; but still the removal, in some specific
form, of excrementitious matter from the system, is a most important
part of the office of each.
860. The skin (34), to which are assigned numerous and highly important
offices, seems to be specially constructed for performing the function
of excretion. It is composed of three layers, of which the internal
is called the cutis, or true skin; the external the cuticle, or scarf
skin; and the middle, by which the other two are united, the rete
mucosum. The latter is indistinct, excepting in the negro, in whom it
is the seat of colour.
861. The cutis, or true skin, is a dense membrane, composed of firm
and strong fibres, interwoven like a felt. Its internal surface is
marked by numerous depressions, which receive processes of the adipose
tissue beneath. Over its external surface is spread a delicate and
complex net-work of vessels, termed the vascular plexus, of such
extent and capacity that, in the natural state of the circulation, a
very large proportion of the whole blood of the body is constantly
flowing in these blood-vessels of the cutis. A prodigious number of
nerves accompany the cutaneous blood-vessels, some derived from the
organic, and others from the sentient portion of the nervous system.
The organic nerves endow the arteries with the power of performing
the organic processes proper to the cutis, which are principally of
an excrementitious nature. The sentient nerves communicate to every
point of the external surface of the cutis the exquisite degree of
sensibility possessed by the skin. Innumerable absorbent vessels
terminate at the same points, with the capillary arteries and the
sentient nerves.
862. The extreme smoothness and softness natural to the skin is
communicated to it by a number of follicles which are placed in the
cutis, and are termed sebaceous, from the oily substance they secrete.
It is the matter secreted by these organs which communicates to the
animal body the odour peculiar to it, on which the scent depends.
863. In many parts the cutis is perforated obliquely by hairs, which
spring from little bulbs beneath it, to which the growth of the hairs
is confined. The human hair, which is hollow, consists of fine tubes
filled with an oily matter. This matter is either of a black, red,
yellow, or pale colour, as the hair is black, red, yellow, or white.
864. The nails are products formed by the cutis, and are essentially
the same as the cuticle.
865. By long-continued boiling the cutis is resolvable into gelatin,
which by evaporation becomes glue, and by combining with tannin and the
extractive of oak bark is converted into leather.
866. The third portion of the skin, the cuticle, is a thin, elastic
membrane spread over the external surface of the cutis, from which it
is easily detached, by the action of a blister in the living, and by
the process of putrefaction in the dead body. It is without vessels and
nerves, and consequently it is insensible and inorganic. It is formed
as a secretion by the cutis, and is composed almost entirely of solid
albumen. When any portion of it is removed, it is renewed with great
rapidity. Since it is subject to constant waste from friction, and is
much increased by pressure, as is manifest in the palms of the hands
and the soles of the feet, its formation must be continual; yet even in
the fœtus it is thicker in the parts where pressure is ultimately to be
made than in the other parts of the body.
867. The cuticle is a sheath in which the body is enclosed for the
purpose of restraining the organic actions which take place at its
surface, and for tempering the sentient impressions received there. For
restraining the organic actions it is fitted by the cohesion of its
parts, which is such as to receive and transmit any fluid very slowly,
as is manifest from the dryness of its surface when it is raised in
a blister, and from the extreme rapidity with which the cutis dries,
until it becomes as hard as parchment, when the cuticle is removed from
it in the dead body.
868. Diffused over every part and particle of the cutis is the seat
of common sensation, that cognizance may be taken of the presence of
external objects. Restricted to particular points, the tips of the
fingers, is the seat of one of the special senses, that of touch.
Had the nerves which communicate to this extended surface its acute
sensibility been placed in direct contact with external bodies,
intolerable pain would have been the result; but by covering this
surface with an inorganic and insensible substance, yet so thin that it
is a pellicle rather than a membrane, the organ of sense is shielded,
while the delicacy of the sensation is not impaired. But the control
of the organic process and the protection of the sentient nerve are
not the only offices performed by the cuticle; it serves further to
hide what it is undesirable to have constantly in view. All that is
beautiful in the blood as an object of sense is rendered visible
through the cuticle, in the bright and rosy hue of health, at the same
time that every process, the sight of which would excite anxiety or
terror, is effectually concealed.
869. The skin, an organ of secretion, an organ of absorption, an organ
of excretion, and an organ of sense, is thus the immediate seat of
three organic processes and of one animal process.
870. The chief excretion performed by the skin, in the human body, is
commonly known under the name of perspiration. The perspiration is
either sensible or insensible. Sensible perspiration is the liquid
commonly called the sweat. Insensible perspiration consists of a vapour
which, under the ordinary circumstances in which the body is placed,
is invisible. The invisible vapour is constantly exhaling; the visible
liquid is only occasionally formed. The quantity of matter carried out
of the system under the form of invisible vapour is much greater than
that lost by the visible liquid.
871. That a quantity of matter is incessantly passing off from the
surface of the skin, under the form of an invisible vapour, is proved
by the following facts:—
1. If the hand and arm are enclosed in a glass jar, the inner surface
of the glass soon becomes covered with moisture.
2. If the tip of the finger be held at about the twelfth of an inch
from a mirror, or any other highly polished surface, the surface
rapidly becomes dimmed by the vapour which condenses upon it in small
drops, and which disappear on the removal of the finger.
3. If the body be weighed at different periods, an accurate account
being taken of the ingesta and the egesta, it is found to undergo a
loss of weight sensibly greater than can be attributed to any of the
visible discharges: this loss must be owing to the transmission of a
quantity of matter out of the body, under the form of invisible vapour.
872. The matters excreted under the form of perspiration are separated
from the blood by a true and proper secretion, like the other
secretions of the body. The process by which this is effected is called
transudation. The matter of transudation deposited on the surface of
the skin by a vital function is removed from the body by evaporation,
a physical process which consists of the conversion of a liquid
into a vapour by the addition of heat. Consequently the process of
perspiration is a cooling process, and it is chiefly by the increase of
the perspiration that the body is enabled to bear the intense degrees
of heat which it has been shown (491, _et seq._) to be capable of
sustaining. Sitting one day in repose in the shade during the intense
heat of an American summer’s day, the skin freely perspiring at every
pore, Dr. Franklin happened to examine the temperature of his body with
a thermometer. He found that the temperature of his body was several
degrees lower than that of the surrounding air. The physiologists who
exposed themselves in heated chambers, for the sake of ascertaining the
greatest degree of heat which the human body is capable of enduring,
perspired profusely during the experiment (495). The artisans who
carry on their daily occupations in elevated temperatures perspire
most profusely (884, _et seq._). Under such circumstances, caloric is
communicated to the human body just as freely as to inorganic matter
yet it does not injure the body, because it does not accumulate in the
system, but is immediately expended in supplying the heat necessary
to convert the water, which is poured out upon the skin, into vapour.
In this manner that surface of the body at which, under ordinary
circumstances, a large portion of its animal heat is generated, is
the very surface at which, under extraordinary circumstances, cold is
generated, and the heat of the system positively reduced.
873. The physical process of evaporation would go on to a certain
extent, though the vital function of transudation did not exist, and
does go on in the dead body when the vital function is at an end. An
organic tissue enclosing a liquid may not be porous enough to give
passage to a single drop of liquid, and yet sufficiently porous to
admit air. In this case the air in contact with the tissue dissolves
the liquid in its interior, and carries it off in the form of invisible
vapour; hence liquids contained in organic bodies in contact with the
air diminish in quantity by evaporation. But if an animal be placed
in air saturated with moisture, and of the same temperature as its
own, the air can no longer deprive that animal of a single particle of
its moisture: evaporation from the body, in such a condition of the
air, is suppressed. On the other hand, when an animal is placed in
air saturated with moisture, and of the same temperature as its own,
so far is transudation from being suppressed, that the sweat streams
from every part of the external surface of the body. By modifying
the condition of the air, in regard to its hygrometrical state and
its temperature, the result of the physical process and of the vital
function may thus be separated from each other, and the amount of each
may be ascertained with perfect exactness. Now, by numerous experiments
on the cold-blooded vertebrata, placed under such conditions of the
air, it is found that, in these animals, perspiration by evaporation is
to that by transudation as 6 to 1. But since the human body presents to
the air an immense extent of surface over which is constantly flowing
a large proportion of the whole quantity of blood contained in the
system, the loss by the physical process compared with that by the
vital function must be still greater in man than in the cold-blooded
animal.
874. Taking together the average quantity of matter removed from
the human body by both processes, or the whole loss of weight
sustained from perspiration, on the comparison of the results of
many observations, it is estimated to vary from twenty ounces in the
twenty-four hours of the colder, to forty ounces in the warmer climates
of Europe. Keill estimated it at thirty-one ounces. In the climate of
Paris it is stated to be thirty ounces.
875. By the delicate tests of modern chemistry, various substances are
found to be contained in the aqueous fluid which constitutes the great
proportion of the matter of perspiration, namely, an acid, probably the
lactic, a small proportion of animal matter, some alkaline and earthy
salts, an oily or fatty substance, probably derived from the sebaceous
follicles. All these matters are so analogous to the constituents of
the serum of the blood as to leave little ground for doubt that they
are merely separated from this part of the blood as it is flowing
through the complex net-work of vessels spread over the surface of the
cutis (861).
876. The skin, when in contact with the air, also separates a portion
of carbon from the blood, and to the extent in which it does this it
is auxiliary to the lungs; but the quantity of carbonic acid excreted
by the skin is small and variable in amount. The primary office of
the skin as an organ of excretion is to relieve the blood of its
superabundant watery particles, that is, to remove from the system its
superfluous hydrogen.
877. A full account has been given (359, _et seq._) of the primary
office of the lungs, which, it has been shown, is to decarbonize the
blood. The details of the calculations have been stated (457), from
which it is estimated that 10 ounces and 116 grains of carbon are daily
exhaled by the lungs under the form of carbonic acid; and the reasons
have been assigned which favour the conclusion that the carbonic acid
expired is not formed immediately in the lungs by the combination of
the oxygen of the atmospheric air with the carbon of the blood; but in
the system, where the oxygen taken into the blood at the lungs unites
with carbon, the carbonic acid resulting from the combination passing
as soon as formed into the capillary veins. The blood contained in
these vessels, thus become venous, returns to the lungs, where it gives
off the carbonic acid accumulated in it, and by that depuration again
assumes its arterial character.
878. Some interesting experiments performed by Dr. Stevens appear
to show that there exists a powerful attraction between oxygen and
carbonic acid, and that the venous blood, as it is flowing through the
lungs, is freed from its carbonic acid by virtue of that attraction.
Chemists were so universally agreed that the carbon in carbonic acid is
united with its maximum dose of oxygen, that the idea of an attraction
between carbonic acid and oxygen appeared highly improbable. The
evidence of the fact, however, is decisive. If a receiver, filled with
carbonic acid, and closed by a piece of bladder, firmly tied over it,
be exposed to the atmospheric air, the carbonic acid, notwithstanding
its superior specific gravity, rapidly escapes, and does so without
the exchange of an equivalent portion of atmospheric air; the bladder
is consequently forcibly depressed into the receiver. If the converse
of this experiment be tried, and the receiver, containing atmospheric
air, be tied over with a piece of bladder or thin leather, and then be
immersed in carbonic acid, this gas will so abundantly penetrate the
membrane and enter the receiver as to endanger its bursting.
879. Dr. Stevens had repeated opportunities of verifying these facts,
during a stay which he made at Saratoga, in the United States, the
springs at which place liberate a large quantity of carbonic acid.
In the high rocks it often collects in considerable quantity and
purity, and experiments on dogs and rabbits are often made for the
entertainment of strangers, as at the Grotto del Cano, near Naples.
This rock stands by itself in a low valley, through which there run two
currents of water, the one fresh and superficial, the other beneath
and charged with salts and carbonic acid. A current of this water rises
to some height in a cavity of the high rock, which appears to have been
formed by a deposition of earthy salts from the water. It has a conical
figure, the base of which is below the surface of the ground, and is
about nine feet in diameter. It rises about five feet from the ground,
where it is truncated, and presents an aperture a foot in diameter. The
water rises in general only about two feet above the ground, and in the
three feet above the surface of the water the liberated carbonic acid
collects. By luting a large funnel over the aperture, carbonic acid may
be collected at the mouth of the funnel in indefinite quantities, of
which Dr. Stevens availed himself to multiply and vary his experiments,
the result of which appears to be the complete establishment of the
fact that there exists a powerful attraction between carbonic acid and
oxygen.
880. The application of this fact to the explanation of the phenomena
of respiration is highly interesting. By virtue of this mutual
attraction, two currents are established, which flow in opposite
directions, through the membranous matter of the air-vesicles of the
lungs and the pulmonary blood-vessels spread out upon their surface;
the oxygen of the air flows to the blood attracted by its carbonic
acid, and the carbonic acid of the blood flows to the air attracted by
its oxygen. According to Dr. Stevens, the moment the blood parts with
its carbonic acid it loses its dark colour, and becomes of a bright
vermilion colour, for the following reason: all acids impart a dark
colour to the blood. With respect to most acids, this colour remains,
although the added acid be afterwards saturated. Carbonic acid forms an
exception, for on the removal of this aërial acid the blood resumes its
bright and arterial colour. Alkalies, like acids, darken the colour of
the blood, but salts produce a bright and vermilion colour when added
to the colouring matter of the blood. When the blood loses its carbonic
acid, the salts contained in the blood produce upon its colouring
matter the vermilion tint natural to the combination when the influence
of the salts is not counteracted by the presence of a redundant acid.
At the moment the venous blood gives up its carbonic acid it receives
in exchange a portion of the inspired air, which is chiefly at the
expense of the oxygen. It retains somewhat more oxygen than it yields
back in the shape of carbonic acid. The reddened and oxygenated blood,
having returned to the heart, is diffused over the system, where
it parts with its oxygen and combines with carbon, forming by the
union carbonic acid; the necessary result of this combination is the
generation of animal heat in the exact proportion to the quantity of
the carbonic acid which is produced. The venous blood, which receives
the carbonic acid as it is formed in the system, is darkened by its
presence, which counteracts the effects of the salts of the blood upon
its colouring matter.
881. An account has been given (439) of the experiments, which prove
that the lungs also constantly exhale a quantity of azote.
882. It has been further shown (469) that, together with the carbonic
acid, which passes off in the inspired air, there is always present a
quantity of aqueous vapour. This aqueous vapour is not visible at the
ordinary temperature of the air in its ordinary hygrometric state,
because the water is then dissolved in the air, and is carried off
in the form of invisible vapour; but it becomes abundantly manifest
at a low temperature, or when the air is loaded with moisture. By
the removal of this aqueous vapour, the lungs assist the skin in the
depuration of the blood. The water transpired by the lungs, like that
perspired through the skin, is separated from the blood by a true
and proper secretion constituting the pulmonary transudation. It is
commonly estimated that the lungs exhale about one-third as much as
the skin, or fifteen ounces daily. Dalton estimates it at twenty-four
ounces.
883. These estimates of the quantity of fluid lost by cutaneous
and pulmonary transpiration relate to the quantities lost at the
ordinary external temperatures in which the human body is placed. The
quantity lost when the body is exposed to an elevated temperature is
prodigiously increased. It did not occur to the physiologists, whose
experiments have been detailed (492, _et seq._), to ascertain this
by causing themselves to be accurately weighed immediately before
they entered their heated chamber and immediately after they left it.
Having heard that the loss daily sustained by the workmen employed in
gas-works is very extraordinary, I endeavoured to ascertain the amount
of it with exactness. This I have been enabled to accomplish by the
assistance of Mr. Monro, the manager of the Phœnix Gas Works, and of
Mr. Cooper. The following are the experiments by which this has been
ascertained.
EXPERIMENT I.—November 18, 1836, at the Phœnix Gas Works, Bankside,
London.
884. Eight of the workmen regularly employed at this establishment in
drawing and charging the retorts and in making up the fires, which
labour they perform twice every day, commonly for the space of one
hour, were accurately weighed in their clothes immediately before they
began and after they had finished their work. On this occasion they
continued at their work exactly three-quarters of an hour. In the
interval between the first and second weighing, the men were allowed
to partake of no solid or liquid, nor to part with either. The day was
bright and clear, with much wind. The men worked in the open air, the
temperature of which was 60° Farh. The barometer 29° 25´ to 29° 4´.
Weight of the Men Weight of the Men Loss.
before they began after they had
their work. finished their work.
cwt. qr. lbs. oz. cwt. qr. lbs. oz. lbs. oz.
Michael Griffiths 1 1 14 10 1 1 12 2 2 8
John Kenny 1 0 26 10 1 0 24 1 2 9
John Ives 1 0 14 2 1 0 11 8 2 10
James Finnigan 1 1 10 6 1 1 7 0 3 6
William Hummerson 1 0 24 4 1 0 20 8 3 12
Timothy Frawley 1 1 8 10 1 1 4 12 3 14
Patrick Nearey 1 1 14 10 1 1 10 8 4 2
Bryan Glynon 1 1 0 4 1 0 24 1 4 3
EXPERIMENT II.—Nov. 25, 1836.
885. Day foggy, with scarcely any wind. Temperature of the air 39°
Farh., barometer 29° 8´. On this occasion the men continued at their
labour one hour and a quarter.
Before. After. Loss.
cwt. qr. lbs. oz. cwt. qr. lbs. oz. lbs. oz.
Patrick Murphy 1 1 0 0 1 0 27 2 0 14
John Broderick 1 0 9 4 1 0 8 0 1 4
Michael Macarthy 1 0 11 9 1 0 10 3 1 6
Michael Griffiths 1 1 15 8 1 1 13 2 2 6
James Finnigan 1 1 12 4 1 1 9 12 2 8
Bryan Duffy 1 1 11 12 1 1 9 0 2 12
John Didderick 1 1 11 5 1 1 8 8 2 13
Charles Cahell 1 1 4 5 1 1 1 6 2 15
886. Charles Cahell, the man who on this occasion lost the most, was
weighed previously to the commencement of his work, with all his
clothes off, excepting his shirt, which was kept dry and put on him
again when weighed a second time at the end of his work. He was then
immediately put into a warm bath at 95° Farh., and kept there half an
hour: he complained of being weak and faint, and when reweighed had
gained half a pound.
EXPERIMENT III.—June 4, 1837.
887. Day clear, with some wind. Temperature 60° 5´.
Before. After. Loss.
cwt. qr. lbs. oz. cwt. qr. lbs. oz. lbs. oz.
Robert Bowers 1 1 19 0 1 1 17 0 2 0
William Mullins 1 1 3 0 1 1 1 0 2 0
Charles Cahell 1 1 2 0 1 1 0 0 2 0
John Kenny 1 0 22 2 1 0 19 8 2 10
Bryan Glynon 1 0 27 0 1 0 24 4 2 12
John Haley 1 1 4 0 1 1 1 4 2 12
Benjamin Faulkner 1 1 15 14 1 1 13 0 2 14
Michael Griffiths 1 1 8 8 1 1 5 8 3 0
John Broderick 1 0 4 6 0 3 27 8 4 14
John Didderick 1 1 6 12 1 1 1 10 5 2
888. The two last men worked in a very hot place for one hour and ten
minutes; all the rest worked about one hour. Michael Griffiths, as
soon as he had finished his work, was put into a bath at 98°, where he
remained half an hour. He was reweighed on coming out of the bath, and
had lost 8 oz.
889. From these observations it appears that, towards the end of
November, when the temperature of the external air was 39°, and the day
was foggy and without wind, the greatest loss did not amount to 3 lbs.
(2 lbs. 15 oz.), the least loss was 14 oz., and the average loss was 2
lbs. 3 oz.
890. In the middle of the same month, when the temperature of the air
was 60°, and the day was clear with much wind, the greatest loss was 4
lbs. 3 oz., the least loss was 2 lbs. 8 oz., and the average loss was 3
lbs. 6 oz.
891. In June, when the temperature of the external air was 60°, and the
day exceedingly bright and clear, without much wind, the greatest loss
was 5 lbs. 2 oz., the next greatest loss was 4 lbs. 14 oz., the least
loss was 2 lbs., and the average loss was 2 lbs. 8 oz.
892. The same individuals lose very different quantities at different
times. Thus, James Finnigan in the first experiment lost 3 lbs. 6 oz.,
in the second 2 lbs. 8oz. Michael Griffiths in the first experiment
lost 2 lbs. 8oz., in the second 2 lbs. 6 oz., and in the third 3 lbs.;
while John Kenny in the first experiment lost 2 lbs. 9 oz., and in the
third experiment, which was the second to which he was subjected, he
lost very nearly the same, namely, 2 lbs. 10 oz. On the other hand,
Bryan Glynon in the first experiment lost 4 lbs. 3 oz., and in the
third experiment, which was the second to which he was subjected, he
lost no more than 2 lbs. 12 oz.
893. In one case, when a man who had lost 2 lbs. 15 oz., the greatest
quantity lost by any of the men examined during that day, was put into
a hot bath at 95°, and reweighed on coming out of the bath, where he
had remained exactly half an hour, it was found that he had gained half
a pound. On the other hand, when a man who had lost 3 lbs. was put
into a hot bath at 98°, and kept there for half an hour and reweighed,
it was found that he had lost exactly half a pound.
894. It was our intention to have pursued these experiments, with the
view of ascertaining the influence of the hygrometrical state of the
air on transpiration, as well as the absorbing power of the skin, under
circumstances so favourable to the activity of that power, but the
investigation has been unavoidably postponed.
895. The results of these observations are as interesting in relation
to absorption as to transpiration. Thus, James Finnigan, on the 18th of
November, weighed,
cwt. qr. lbs. oz.
before the experiment 1 1 10 6
after the experiment 1 1 7 0
having lost 0 0 3 6
On the 25th of November he weighed 1 cwt. 1 qr. 12 lbs. 4 oz., having
gained in the interval 1 lb. 14 oz.
Michael Griffiths, on the 18th of November,
cwt. qr. lbs. oz.
before the experiment, weighed 1 1 14 10
after the experiment 1 1 12 2
having lost 0 0 2 8
On the 25th of November, before the experiment, he weighed 1 cwt. 1 qr.
15 lbs. 8oz., having gained 14 oz.; but on the 3rd of June he weighed
1 cwt. 1 qr. 8 lbs. 8 oz., having lost between the 18th of November and
the 3rd of June, 6 lbs. 2 oz.
896. John Kenny, on the 18th of November,
cwt. lbs. oz.
before the experiment, weighed 1 26 10
after the experiment 1 24 1
having lost 0 2 9
On June the 3rd he weighed 1 cwt. 22 lbs. 2oz., having gained in the
interval 4 lbs. 8 oz.
897. Bryan Glynon, November 18th,
cwt. qr. lbs. oz.
before the experiment, weighed 1 1 0 4
after the experiment 1 0 24 1
having lost 0 0 4 3
On the 3rd of June he weighed 1 cwt. 27 lbs., having lost 1 lb. 4 oz.
898. Thus, in the course of their ordinary occupation, these men are in
the habit of losing from 2 lbs. to 5 lbs. and upwards twice a-day; yet,
when weighed at distant intervals, it is found that some have actually
gained in weight and others have lost only a few pounds; it follows
that the activity of the daily absorption must be proportionate to that
of the daily transpiration.
899. According to the prevalent opinion, the liver is the cause of
a large proportion of the maladies which afflict and destroy human
life. It certainly exercises an important influence over health and
disease, the true reason of which is but little understood by those who
attribute most to its agency.
900. The liver is an organ of digestion and an organ of excretion.
It is an organ of digestion in a two-fold mode:
1. By the secretion of a peculiar fluid, through the direct action of
which chyme is converted into chyle. The several phenomena attending
this operation have been fully described (668 _et seq._).
2. By subjecting alimentary matters which have been partly acted on by
the stomach and intestines to a second digestion.
901. It has been shown (666) that the veins which return the blood from
the digestive organs, the stomach, the intestines, and the mesentery,
together with the veins of the spleen, the omentum and the pancreas,
instead of pursuing a direct course to the right side of the heart in
order to transmit their contents by the shortest route to the lungs, as
is the case with all the other veins of the body, unite together and
form a large trunk termed the vena portæ, which enters the liver and
ramifies through it in the manner of an artery. It has been further
shown (666) that the bile is secreted from the venous blood contained
in this vessel by its capillary branches spread out on the walls of
the biliary ducts, the only known instance in the human body in which
a secretion is formed from venous blood by venous capillaries; that
the trunk of this vein, unlike that of any other, is encompassed with
organic nerves, which accompany its subdivisions, and are spread out
upon its capillary branches just as an organic nerve is spent upon
an artery, and that thus, as this vessel performs the function of an
artery, it has the structure and distribution of an artery.
902. The veins which unite to form the vena portæ take up, by their
capillary branches, certain portions of the contents of their
respective organs, and bear those contents directly into the venous
current. The capillary veins of the stomach take up certain parts of
the contents of the stomach, it would appear the fluid substances
received with the aliment more especially; the capillary veins of the
duodenum take up certain portions of the contents of the duodenum, and
so on of the capillary veins of the spleen, intestines, and all the
organs whose veins combine to form the vena portæ. Further, branches
of the absorbent vessels of these organs have been distinctly traced
opening directly into the veins in their immediate neighbourhood.
Certain products of digestion must, then, be constantly poured, both
by the capillary veins and by the absorbent vessels of the digestive
organs, into the blood of the vena portæ.
903. Accordingly, on the examination of animals soon after a meal,
streaks of a substance like chyle are often observed in the blood of
the vena portæ. It is further established by numerous experiments,
that if alcohol, gamboge, indigo, and other odoriferous and colouring
matters, are mixed with the food, their presence is manifest in the
blood of the digestive organs, and more especially in the blood of the
mesenteric veins and in that of the vena portæ, while no trace of these
substances is ever found in the lacteals.
904. The lacteals, it has been shown (835. 1.), are special organs
appropriated to the performance of a specific function, that of
absorbing chyle. To fit them for this office, they are endowed with an
elective power, by virtue of which they select, from the alimentary
mass, that portion of it only which is converted into chyle; in
a natural and healthy state they would appear to be incapable of
absorbing any other substance excepting pure chyle. But in the
digestive organs there is always present much nutritive matter not
yet converted into proper chyle, and with this matter there are mixed
foreign substances not strictly alimentary. These unassimilated matters
and foreign substances, absorbed by the capillary veins or by the
absorbent vessels, or by both, are conveyed directly into the vena
portæ, by which vessel they are transmitted to the liver, where they
undergo a true and proper digestion. After undergoing this digestion
in the liver, they are sent by a short course to the heart, and thence
to the lungs, where they are assimilated into, or at least commingled
with, arterial blood, and, with arterial blood, are transmitted to the
system. The substances subjected to this hepatic digestion, which is
as real as that effected in the stomach and duodenum, do not appear
to enter the lacteals at all; they have therefore a shorter course
to traverse, and probably a proportionately less elaborate process
to undergo, before their transmission to the lungs and their final
entrance into the arterial system.
905. What the particular substances are for which this slighter
digestive process suffices is not known with certainty. There is,
however, reason to suppose that they consist chiefly of liquids, while
there is direct evidence that vinous and spirituous liquids enter
the system through this shorter course; since these fluids are often
abundantly manifest in the blood of the vena portæ, when not the
slightest trace of them can be detected in the lacteal vessels.
906. According to this view, the liver is a second digestive
apparatus, completing what the first commences, or effecting what
that is incapable of accomplishing; and this view assigns the reason
why certain fluids taken into the stomach sometimes appear in the
secretions and excretions with such astonishing rapidity; why the liver
so constantly becomes diseased when highly stimulating substances, not
properly alimentary, are mixed with the food, and more especially when
ardent spirits or the stronger wines are largely and habitually taken;
why the sympathy is so intimate and intense between the stomach and
the liver and the liver and the stomach, both in health and disease;
why in the ascending animal series the liver so soon appears after
the stomach, and why the magnitude of the organ and the elaborateness
of its structure progressively increase with the extension of the
digestive apparatus and the corresponding complexity of the general
organization.
907. The second function performed by the liver is that of excretion.
The excrementitious matter eliminated from the blood by the liver is
contained in its peculiar secretion, the bile. The bile consists of
two portions, an assimilative part which combines chemically with the
chyle, purifying and exalting its nature; and an excrementitious part
which combines with the residue of the aliment.
908. The excrementitious part of the bile contains a large proportion
of carbon and hydrogen. Carbon and hydrogen abound in venous blood;
venous blood in large quantity is sent to the liver to afford the
materials for the secretion of bile; consequently, the more copious
the secretion of bile the greater the quantity of carbon and hydrogen
abstracted from venous blood. It follows that, by this elimination of
carbon and hydrogen from the blood, the liver is auxiliary, as an
organ of excretion, to the skin and the lungs.
909. But it is well worthy of remark, that although the liver at all
times assists the skin and the lungs in carrying on the process of
excretion, it does this most especially under circumstances which
necessarily enfeeble the action of the cutaneous and pulmonary organs.
910. Less carbon is expelled from the lungs in summer than in winter;
at a high than at a low temperature; consequently by a long-continued
exposure to intense heat, as in the hot months of summer, and still
more by a continual residence in a warm climate, an accumulation of
carbon in the blood is favoured. A part of this excess is removed by
the increased exhalation from the skin. The skin, however, is the
chief outlet, not for carbon, but for hydrogen; and accordingly by the
increased perspiration hydrogen is largely removed. Hydrogen and carbon
compose fat. The deposition of fat, could it go on to the requisite
extent, would afford an adequate consumption for the superabundant
carbon; but the formation of fat is prevented by the dissipation of the
hydrogen. Under such circumstances, when the lungs cannot carry off the
requisite quantity of carbon, nor the adipose tissue compensate for its
diminished activity by the deposition of fat, the liver, taking on an
increased action, secretes an extraordinary quantity of bile. In this
manner the superfluous carbon, instead of being removed in the ordinary
mode, by the pulmonary artery through the lungs, under the form of
carbonic acid gas, is excreted by the vena portæ, through the liver,
under the form of bile, while the superabundant hydrogen is removed by
the increased quantity of perspiration; and thus the accumulation of
these inflammable matters in the system is effectually prevented.
911. By the deposition of fat in the adipose tissue material assistance
is afforded to the excretory action of the skin, the lungs, and
the liver. Fat is composed essentially of carbon and hydrogen; it
contains no nitrogen and very little oxygen. It is deposited whenever
an excessive quantity of nutritive matter is poured into the blood,
and especially when at the same time the different secretions and
excretions ordinarily formed from the blood are diminished. The primary
object of this deposition is to relieve the circulation of a load which
would embarrass and ultimately stop the actions of life. It serves,
however, a secondary purpose, that of forming a storehouse of nutritive
matter, duly prepared for supplying the wants of the system, in case
the body should be placed under circumstances in which the digestive
organs can no longer receive food or no longer convert it into chyle.
912. Thus hybernating animals, which pass many months without taking
food, accumulate a store of fat before they fall into the state of
torpor. Marmots and dormice subsist on this store during the winter,
and hence, when spring awakens them from their torpor, they are always
in a state of extreme emaciation. Birds and other animals which live on
food procured with difficulty in the winter, become unusually fat in
the autumn.
913. During fever and other acute diseases, when little food is
received, and still less converted into chyle, the extreme emaciation
which the body undergoes is owing partly to the disappearance of the
fat, which is taken up by the absorbents and carried into the blood, in
order to compensate for the deficiency of nutrient matter supplied by
the digestive organs.
914. The chief depositories of the fat are those intersticial spaces of
the body in which a certain quantity of soft but tenaceous substance is
required to obviate pressure or to preserve symmetry. A large quantity
is also placed immediately beneath the skin; in the interstices of
muscles; along the course of blood-vessels and nerves; in the omentum,
where it is spread like a covering over the viscera of the abdomen
(fig. CLXX. 7); in the mesentery and around the kidneys.
915. Fat is a bad conductor of heat; consequently the layer which is
spread over the external surface immediately beneath the skin, and
that which is collected in the interior of the omentum, must be useful
in preserving the heat of the body. Fat persons bear cold better than
lean persons. Animals which inhabit the northern climates, and the
fishes of the frozen seas, are enveloped in prodigious quantities of
fat. Where the accumulation of this substance would produce deformity
or interfere with function, as about the joints, in the eyelids, within
the skull, not a particle is ever deposited. About the joints it would
impede motion; in the eyelids it would render the face hideous and
obstruct vision; and within the skull, a cavity completely filled
with the brain, an organ impatient of the slightest pressure, had a
substance been placed, the quantity of which is liable to be suddenly
trebled or quadrupled, changes in the system which now produce no
inconvenience would have been fatal. Thus, while provision is made at
once to exonerate the system from too great a load of nourishment, and
to lay up the superfluous matter, as in a magazine, to be ready for
future use, the most extreme care is taken to deposit the store in safe
and convenient situations.
916. The excretory organs and processes, hitherto considered, have for
their object the removal from the blood of its superfluous carbon and
hydrogen; the element peculiar to the animal body, azote, is eliminated
by the kidneys, glandular organs which possess a highly complex
structure.
917. But besides the removal of the superfluous azote, the fluid
secreted by the kidneys would appear to be a general outlet for
whatever is not required in the system, and for the removal of which
no specific apparatus is provided. Chemical analysis shows that, in
different states of the system, the following substances are contained
in this fluid:—water, free phosphoric acid, phosphate of lime,
phosphate of magnesia, floric acid, uric acid, benzoic acid, lactic
acid, urea, gelatin, albumen, lactate of ammonia, sulphate of potash,
sulphate of soda, fluate of lime, muriate of soda, phosphate of soda,
phosphate of ammonia, sulphur, and silex.
918. This catalogue itself suggests the idea that when any matter
employed in carrying on the functions is in excess, or when it has
become decayed, or is decomposed and is not eliminated by any other
excretory process, it is taken up by the absorbents, poured into the
veins, and so conveyed in the course of the circulation to the kidneys,
by which organs it is separated from the blood, and thence by an
appropriate apparatus carried out of the system.
919. The specific matter secreted by the kidneys is that termed urea;
a substance of a resinous nature, highly animalized. One character by
which the animal is distinguished from the plant is its locomotion.
The organ by which the animal is rendered capable of performing the
function of locomotion is muscle or flesh. The basis of muscle is
fibrin, and the basis of fibrin azote. There must be in the animal
body an abundant supply of fibrin, and consequently a proportionate
abundance of azote. Azote is introduced into the system partly by the
food and partly by the lungs. That there may be a sufficiency for all
occasions, more is introduced than is necessary on ordinary occasions,
and a special outlet is established for the excess through the kidneys.
920. Organs appropriated to the removal of substances from the blood,
capable of becoming deleterious by their accumulation, generally in
a state of health perform their office so perfectly that the matters
which it is their part to excrete are eliminated almost as quickly
as they enter the blood, so that they are seldom present in the
circulating fluid in sufficient quantity to be detected by the most
delicate chemical tests. But by the removal of the excretory organ, or
by the suppression of its function, the excretory matter accumulates
in the blood, and is then readily detected. A decisive experiment
disclosed that this is the case with regard to urea. The kidneys were
removed from a living animal. The operation did not appear to be
productive of material injury for some time; but at length symptoms
denoting the presence of a poison in the blood arose, and the animal
died. The blood was carefully examined after death. It was found to
contain a much larger quantity than ordinary of the peculiar animal
substance which enters into the composition of the serosity of the
blood (225). On subjecting this substance to the action of various
re-agents, and also on reducing it to its ultimate elements, it was
found to resemble urea; to be, in fact, nearly identical with urea as
contained in the urine. From this experiment it became manifest that
the source of the urea is the serosity of the blood. It is probable
that the chief office of the kidney is to separate the urea from the
other ingredients of the blood, and to convey it to the organs which
are destined to carry it out of the body.
921. It is estimated that about a thousand ounces of blood pass through
the kidneys in the space of an hour; itself a sufficient indication
of the importance of the excretion performed by this organ, and an
adequate source of the matter actually excreted, although, under
ordinary circumstances, distributed through the circulating mass in
quantities so minute as to be almost inappreciable.
922. From the power of absorption possessed by the veins of the stomach
and intestines, from the connexion proved to be established between
the venous and absorbent systems, and from the discovery of Lippi, that
several absorbent branches in the abdomen terminate directly in the
pelvis of the kidney, that is now an established fact which was long
a conjecture, that there exists a short route from the stomach to the
kidneys, so that the extreme rapidity with which certain substances
mixed with the aliment appear in the fluid secreted by the kidneys is
no longer a matter of wonder.
923. Out of the body urea putrifies with great rapidity. When retained
in the system by the extirpation of the kidney, or by placing a
ligature around the ureter, such is the septic tendency communicated to
the blood that signs of putrescency become manifest even during life,
and after death all the soft parts of the body are reduced to a state
of putrefaction with extreme rapidity. The suppression of the secretion
in the human body, or the undue retention of the matter secreted,
induces fever of a malignant kind, in which the symptoms that denote a
highly putrid taint in the system are rapidly developed. But for the
labour of the kidney, then, a substance would accumulate in the blood,
which would quickly lead to the decomposition of the body.
924. It has been shown that the mucous membrane which lines the
alimentary canal is studded in its whole extent with glands, which
secrete from the blood a large quantity of fluid, These secretions go
on without interruption, whether food be taken or not, so that there
may be copious alvine evacuations though not a particle of food enter
the stomach; and the separation of the matter eliminated from the blood
by this extended membrane can no more be dispensed with than that by
the skin or the lungs. There is, too, a most intimate sympathy between
the secretion of the membrane that lines the internal surface of the
body and that carried on by its external covering; any disorder of
the one immediately and powerfully disturbs the natural course of the
other: hence the diarrhœa, so often produced by the application of
cold to the external skin, and the diseases of the skin, so constantly
connected with a disordered state of the mucous membrane of the
intestines.
925. It is the special office of the large intestines to prepare for
its removal, and to carry out of the system the residue of the aliment,
together with the excrementitious portion of the bile.
926. It was calculated by Haller, that the different excretory organs
remove from the system every twenty-four hours twenty pounds of matter.
Of this total loss sustained daily by the human body, it was estimated
that four pounds are removed by the skin, four pounds by the lungs,
four pounds by the kidneys, and eight pounds by the intestinal canal.
In this estimate, which is considered too large, especially that
by the intestinal canal, the quantity stated must be understood as
denoting the maximum of each secretion.
927. Supposing the ingesta in twenty-four hours to be of food 6 pounds,
or 96 ounces, and of oxygen retained in the system 4 ounces, in all 100
ounces, it is estimated that the egesta will be, in twenty-four hours,
by the skin, 34 ounces, by the lungs 17 ounces, by the intestines 6
ounces, by the kidneys 40 ounces, and by various other excretions
3 ounces, in all, 100 ounces. These calculations must of course be
taken only as approximations to the truth, and as ascribing rather the
relative than the positive quantities of matter excreted.
928. Whatever be the absolute quantity or the form of the excretions,
it is clear, from the preceding account, that there is constantly
removed from the system by the skin a large portion of hydrogen and
some carbon; by the lungs a large portion of carbon and some hydrogen;
by the liver a large portion of hydrogen and some carbon; by the
kidneys a large portion of azote; by the large intestines the residue
of the aliment; while, by the deposition of fat, the superabundant
nutriment withdrawn from the current of the circulation is laid up in
store in some safe part of the body.
929. Most of the processes which have been described are mutually
compensating and vicarious. Besides the office which each habitually
performs, it is capable of having its action occasionally increased,
for the purpose of supplying the deficiency of one or more of its
fellows. If perspiration by the skin languish, transudation by the
lungs increases; if neither the skin nor the lungs be able to remove
the superfluous hydrogen and carbon, these inflammable substances are
carried out of the system by the liver in an augmented secretion of
bile. If the action of the liver be diminished, that of the kidney is
increased; and if the secretion of urine be suppressed, the secretion
of bile is augmented. When the absorbents are oppressed by the quantity
of fluid poured into the stomach, or when the system is at the point
of saturation, and no absorption can go on, the veins take up the
superfluous liquids, pour them into the circulating current, and bear
them to the kidneys, by which organs they are rapidly separated from
the blood, and carried out of the body. The weakness of one organ is
compensated by the strength of another; the diminished activity of one
process is equalized by the increased energy of some other to which it
is allied in nature and linked by sympathy; and thus the evils which
would result from the partial and temporary failure of an important
function are obviated by some vicarious labour, until the enfeebled
organ has recovered its tone, and the natural balance of the functions
is restored.
930. The condition acquired by the elementary particles of organized
bodies, from their long continuance in the system, which induces the
necessity for their excretion, is not known. The chemical elements
of the excretions are the very same as those which constitute the
organized textures and the nourishment by which they are sustained.
Carbon is the basis of the organized body; yet all living bodies,
without exception, excrete carbon. Oxygen, hydrogen, and azote, also,
without which life cannot be maintained, if retained in the system
beyond a given time, are incompatible with the continuance of life.
During the chemical changes which these elementary particles undergo,
in the course of the vital processes, they appear to enter into some
combination, which is no longer compatible with the peculiar mode in
which they are disposed in organized and living structures. And one
such change, of a very remarkable nature, has been observed, which,
it is conceived, has a considerable share in rendering their constant
expulsion and renovation indispensable.
931. Out of the condition of life the component elements of organized
bodies readily combine so as to form crystals; the peculiar
combinations by which they form the constituent textures of organic
structures are never crystalline. No crystal is ever seen in the seat
of a living and growing vegetable cellule; no crystal is ever found
as a constituent part of animal membrane. Whenever a crystal occurs
in an organized body it is always the result either of disease or of
some artificial process, or else it is an excretion separated from the
nourishing fluid and the useful textures. Every one of these textures
contains, even in its minutest parts, saline and earthy, as well
as vegetable or animal, matter. Why do not these saline and earthy
particles as readily combine to form crystals in the organic as they do
in the inorganic body? They never do. In the organic body these saline
and earthy particles are always so arranged that they are diffused
through the membranous fibres or cells, never concentrated in crystals.
932. On the other hand, the elements containing the peculiar matters of
excretion are generally in such a state of combination as readily to
assume the crystalline form, either alone or in the simplest further
combinations of which they are susceptible. It seems probable that this
circumstance may be, at least in part, the cause which necessitates
their expulsion, and it is certain that some such general principle
must determine the incompatibility of the matters of excretion with the
life of the structures
933. The ultimate object of the processes included in the function of
excretion is to maintain the nutritive fluid in a certain chemical
condition. Into the combination of the blood there must enter certain
constituents, and these must be in certain relative proportions, and
in no others. If the salts be diminished or in excess, if the fibrin,
or the red particles, or the serum be abundant or defective beyond a
certain degree, either the necessary chemical elements are not present,
or not present in the form necessary to their entering into the
requisite combinations; the result is, that a proper nutritive fluid
is not formed, and consequently due nourishment is not afforded to the
textures nor due stimulus to the moving powers; there is either too
much nutriment and stimulus or too little; in the one case the machine
is exhausted and worn out, and in the other it is clogged and stopped.
934. The capillary arteries of the skin, and of all the other tissues
into the composition of which gelatin enters as a constituent,
necessarily pour carbon into the capillary veins at the moment they
convert albumen into gelatin (539). The veins, receiving in their
course more and more carbon from the arteries, at length become loaded
with this element, and in order to get rid of the excess they bear
it to the lungs, where it is expelled by the act of expiration under
the form of carbonic acid gas. On the other hand the chyle, gradually
becoming firmer and more condensed by the series of changes which it
undergoes from its first formation in the duodenum to its admixture
with the lymph in the receptacle of the chyle, and with the blood
in the subclavian vein, is hurried to the heart and thence to the
lungs, where it gives off a large portion of its watery particles,
also by the act of expiration, under the form of aqueous vapour. This
excretion of its watery particles is a necessary part of the process of
completion by which the weak albumen of the chyle is converted into the
strong albumen of the blood (703. 3). How completely analogous then is
this excretory process in the plant and in the animal! How precisely
the same is the action of the leaf and of the lung! The leaf dissipates
the superfluous water of the crude sap, concentrates its organic
principles, and brings it into the chemical condition which constitutes
the proper juice of the plant; the lung removes the superfluous water
of the chyle, concentrates its organic principles, and completely
assimilates its chemical nature into that of the blood.
935. It is the same with every other process of excretion; its uniform
result is to alter the chemical composition of the nutritive fluid, to
restore it to a state of concentration and purity. Excretion then is
appropriately termed a depurating process.
936. The effect of the suppression of excretion, when the suppression
is complete, is appalling. Stop the respiration, that is, suspend
the depurating action of the lungs, carbon accumulates in the venous
blood; carbon mixes with the arterial blood; in half a minute the
blood flowing in the arteries is evidently darkened; in three-quarters
of a minute it is of a dusky hue; in a minute and a half it is quite
black; every particle of arterial blood has now disappeared, and the
whole mass is become venous. With the first appearance of the dusky hue
great disturbance is produced in the system; the instant it becomes
dark sensibility is abolished; in a few minutes after it is black the
power of the heart is so enfeebled that it can no longer carry on the
circulation, and in a few minutes more its action wholly ceases, and
can never again be excited. The brain feels the poison first, and is
first killed; but the heart cannot long resist the fatal influence.
937. Stop the excretion of the kidney by the extirpation of the organ,
or the suppression of its secretion, urea accumulates in the blood; the
poison, after a short time, begins to work; fever is excited, and then,
with fearful rapidity, fever is followed by coma, and coma by death.
938. Stop the secretion of bile, a poison accumulates in the blood as
potent, producing insensibility and death as rapidly, as that generated
by the suppression of the depurating action of the kidneys.
939. Only obstruct the secretion of bile, merely prevent its due
elimination from the blood, just in proportion to its suppression does
the system suffer from languor, lassitude, and inaptitude for every
muscular and mental exertion.
940. How do the internal organs suffer when the excretion of the skin
is deficient, and how numberless and hideous are the diseases of the
skin when the depurating process of the alimentary canal is suspended!
941. When, on the contrary, all these excretions are well and duly
performed, how regular and tranquil, yet how full and strong the flow
of the circulating current; how rich the stream poured by it into every
organ; how healthfully exciting its influence on them all; how gentle,
how efficient, every organic action; how complete the absence of all
note or sensible intimation that any such action is going on, yet how
delicious the consciousness produced by its soundness and vigour; how
acute the sense, how bounding the motion, how quick the percipience;
how the pure blood mantles in the cheek and diffuses its sparkling
colour over all the transparent complexion; how the jocund spirits
laugh from the eyes; how the intellectual and sympathizing mind beams
forth from them with a higher and holier happiness! How wonderfully
beautiful is such a human body, and how magnificently endowed in its
capacity to give and to receive enjoyment!
942. There are two adjustments, with regard to the excretions, carried
on by organized bodies, which can never be contemplated with sufficient
admiration. It has been fully shown (464 _et seq._) that the relation
established between the two great classes of organized beings is such
that the excrementitious matter of the plant is nutritious to the
animal, and the excrementitious matter of the animal is nutritious to
the plant; and, consequently, that the two orders of living beings
maintain the world, which is given them as their inheritance, in a
state of perpetual adaptation for the life and health of each other;
the animal receiving healthy stimulation from that which is poisonous
to the plant, and the plant being nourished by particles which the
animal throws off as exhausted and useless. And this relation naturally
suggests that so beautifully described by Milton:—
Flow’rs and their fruit,
Man’s nourishment, by gradual scale sublimed
To vital spirits aspire, to animal,
To intellectual; give both life and sense,
Fancy and understanding; whence the soul
Reason receives.
943. Secondly, the particles thrown off by organized bodies are
rendered, in the very act of their dissipation, subservient to purposes
of utility and pleasure. How these poisonous elements are converted
into the pabulum of life and health has been shown. To a being with the
senses and faculties of man, how loathsome might these particles have
been rendered during the period of their transition from one organized
kingdom to the other! And if disagreeable at all, how constantly forced
upon his sense, wherever he might be, during every moment of his
waking hours, must these objects of disgust have been! But how does
the matter actually stand? The excretions of the plant are the very
particles that, poured
“Into the blissful field through groves of myrrh,
And flow’ring odours, cassia, nard, and balm,”
create “a wilderness of sweets.” It is as these exhalations are passing
off from the economy to which, if retained, they would be noxious
(851), that they become
“Exhalations of all sweets
That float o’er vale and upland;”
and which refresh and delight even more than the forms and colours of
the “aery leaf” or “the bright consummate flower.”
944. And the human body, when the functions of its economy are sound
and vigorous, is fresh and fragrant as the flower (862); and by that
intellectual faculty by which man is capable of associating his
conception of beauty and delight with whatever object has been the
source of exquisite gratification, the fragrance of the flower is but
suggestive of what, to him, is inexpressibly sweeter and dearer.
“As new waked from soundest sleep,
Soft on the flow’ry herb I found me laid
In balmy sweat, which with his beams the sun
Soon dry’d——
By quick instinctive motion up I sprung,
——— And upright
Stood on my feet.——
——— All things smiled
With fragrance, and with joy my heart o’erflow’d.
Myself I then perused, and limb by limb
Survey’d, and sometimes went, and sometimes ran.
With supple joints, as lively vigour led.” MILTON.
——Fresh lily,
’Tis her breathing that
Perfumes her chamber thus. SHAKSPEARE.
—— The very air
With her sweet presence is impregnate richly,
As in a mead that’s fresh with youngest green
Some fragrant shrub exhales——
Ambrosial odours——
Charming present sense,
And sure of memory;—so her person bears
A natural balm—distilling incense.
“Death of Marlowe,” by R. H. HORNE.