be a still more obscure one. Its habitual
ingestion seems to facilitate the process of
fattening, as well as to increase the amount
of excretion. The large constituent which it
forms in the ash of the blood and of most of
the tissues, probably has some reference to
all these details.
The other seasonings chiefly made use of
in civilized life may be divided into two
classes ; acids, and acrid substances. The
former consist of various organic acids ; espe-
cially acetic acid or vinegar, and lemon
juice. These seem to act mainly by stimu-
lating the stomach ; perhaps increasing the
acidity, and with this the solvent energy, of
the gastric juice. The various acrid sub-
stances mustard, pepper, capsicum, garlic,
&c. are also supposed to stimulate the
secretion of this fluid, by exciting a violent
determination of blood to the mucous mem-
brane of the stomach. Many of them are
irritant poisons, when taken in undue quantity.
Stimulants. Tea, coffee, and alcohol, are
substances which, though taken with the
food, are scarcely alimentary in any truer
sense than some of the acrid seasonings just
alluded to. Indeed, were the practice of
chewing tobacco as prevalent as the use of
these substances -f, the leaf of this highly
poisonous narcotic would be equally entitled
to rank in the category of food. Still their
* Compare pp. 332. and 349.
t An instance of the partial starvation of a large
ship's crew on a long voyage was lately brought
under the authors notice, in which the chewers of
tobacco were alleged to have endured hunger far
better than the other sufferers: whilst the smokers
of this narcotic did not enjoy the same advantage.
896
STOMACH AND INTESTINE.
habitual ingestion in company with other
articles of diet, and the manner in which they
modify nutrition, forbid them to be passed
over unnoticed.
Tea and Coffee. Tea and coffee present
a marked similarity, not only in their com-
position, but also in that action on the ner-
vous system which is their chief physio-
logical effect on the organism. Both consist of
an oil, with a certain quantity of tannin, united
to an azotized vegetable alkaloid ; which
is called thein, or caffein, respectively, but
possesses the same composition in both (C 46
H 10 N 4 O 4 ). As regards their effects on the
system, both produce sleeplessness and cere-
bral excitement. But coffee stimulates the
circulation much more strongly, and in some
persons excites diarrhoea. While tea is more
apt to produce muscular tremors and irre-
gular cardiac action ; and generally causes
a constipation rather than a relaxation of the
bowels. The dietetic use of the two is very
similar. How far they promote digestion is
doubtful. They seem, however, to lessen
the drowsiness and cerebral inaction which
often follow the ingestion of a large meal.
Like alcohol, they probably* diminish the rate
of waste of the tissues generally.
Alcohol in all its various forms whether of
beer, wine, liqueur, or spirits is equally un-
deserving of the name of food. It is not a
nutritious article of diet ; but rather a drug,
which has a specific stimulating action on
the nervous system. As regards its ultimate
destiny in the organism, it seems certain that a
part of it leaves the body, unchanged, in the
exhalations of the skin and lungs.
The fermented liquors enumerated above
are generally taken with the food. And in
many of them, the alcohol is associated
with small quantities of sugar and other
alimentary substances. Their several tastes
and odours are due partly to these, partly
to other admixtures : such as the bitter
of the hop in beer, oenanthic aether in wine,
and the various products of distillation in
ardent spirits. The per centage of alcohol
in these different liquids may be estimated as
being, on an average, 3 to 7 in beers ; 7 to 20
in wines ; and 20 to 50 in spirits.
Dietaries. In ending this cursory view of
the different alimentary substances, we may
briefly inquire into the quantity and quality of
the food which would be the result of their
admixture with each other, in the proportions
best suited to the maintenance of health.
From what has already been stated, it is
obvious that, in constructing such an ideal
diet, or in estimating the proper daily ration
which ought to form the food of any indivi-
dual or class of persons, it should be our first
care to ascertain the presence of all the ali-
mentary principles in suitable proportions.
* Since the above was written, the experiments
of Boecker, Lehmann, and others, on which this
statement may now be regarded as based, have
been well discussed in an article in the Medico-
Chirurgical Review for January, 1855.
At first sight, it might seem easy to cal-
culate an efficient scale of diet, from no
other data but those which the above law
affords us. With these data, it might even
appear that such a knowledge or' arith-
metic as is implied in knowing the rules of
simple addition and subtraction would enable
us to calculate an infinite number of dietaries.
For, it would evidently be easy for us to take
any forms of protein, hydrocarbon, or hy-
drate of carbon, and compare the known
per-centage of their elementary substances
with the similar elements of the carbonic acid
and urea which represent the most important
products of the waste of the body. Adapting
the quantities of the former to those of the
latter, we might thus arrange thousands of for-
mulae, in which food would always cover waste,
and income exceed expenditure : formulae
which, provided the human organism were
really made up of similar figures, would, no
doubt, give us equally definite and satisfactory
results when carried out into practice.
A variety of circumstances, however, concur
to invalidate such calculations, and reduce
them to their true value: viz. the results of
a mere process of addition and subtraction,
that only distort and obscure the facts on
which they are founded. Such circumstances
prove, that the end of these sums in simple
arithmetic is no better than the beginning:
that they do but repeat, in a less specific, and
therefore less truthful form, the various state-
ments of the skilful chemist, on which they
are all based ; and that, if carried any further,
they can only mislead the physiologist.
For instance, not all our existing know-
ledge of the composition of most of the sub-
stances commonly used as food, would enable
us to construct a diet which would be certain
to contain an exact proportion of all the
necessary salts. For, in the first place, we
must recollect the probable importance of
some which are only present in very small
quantity ; as well as the value that similarly
appears to attach to minnte proportions of
certain organic acids, and their compounds
with bases. In the next place, we must re-
member that, both in animals and vegetables,
these saline constituents seem liable to vary,
in nature as well as amount, according to the
peculiarities of the soil from which they are
ultimately derived. It is not by any means
easy to insure their presence. And a good
scale of diet ought to provide against any
danger of their deficiency, by adding so
much of various fresh vegetables as would
cover all possibilities of such an occurrence.
Indeed, nothing short of such variety would
make the saline quality of any food perfect.
A similar argument will apply to the quan-
tities of all the other ingredients. The mecha-
nical state of the protein and hydrate of carbon
will have at least as much influence in deter-
mining their requisite amount as the quantity
rendered necessary by the waste of the tissues.
Hence, to this latter estimate we have always
to add a large excess ; such as will be sufficient
to cover the surplus protein which passes,
STOMACH AND INTESTINE
397
undigested or indigestible from the alimentary
canal. And the same caution may be applied,
with still more force, to that substitution of
hydro-carbon, or fat, for hydrate of carbon, or
starch and sugar, which some authors have
regarded as so easy and natural an exchange.
In all probability these substances are not
by any means convertible or inter-changeable
in any scale of diet. The cell- wall of the
adipose tissue is dissolved with great diffi-
culty; its liberated contents are next ab-
sorbed in but small quantities ; and they then
pass through glands which apparently have a
slow but definite office to execute upon them,
before they are admitted into the general
circulating current of the blood. And, lastly,
the rudest numerical contrast of their final
combustive metamorphosis with that of the
hydrates of carbon, shows that they require
the combination of a much larger quantity of
oxygen * before they can leave the body in
the form of carbonic acid and water.
The total amount of food required by the
body is also exposed to circumstances which
are just as certain to baffle all such calcu-
lations. For this important quantity will evi-
dently vary with the rate of waste sustained
by each individual : and hence with the
activity of his life ; the nature of his habitual
exertion; and the state of his mind ; as well
as with the climate, race, temperament, and
education, which help to form the microcosm
of every man's personality. The degree of
variation which may be brought into play
by each of these circumstances it is impossible
to specify ; though it would often receive no
inapt illustration from a comparison of the
habits of the various members of a family or
other smallest social aggregate.
Hence the true value of physiological che-
mistry, in respect to the principles of dietetics,
is that of being an admirable guide to the
general composition of a proper food. In this
capacity, it is not too much to say that its
veto ought to be absolute. But with this
negative function terminates its practical use-
fulness. Our choice of the exact quantities
and qualities of alimentary substances neces-
sary to construct a perfect scale of diet, may
indeed be sometimes explained by chemistry.
But it must always be dictated by experience.
And the dietaries of gaols, workhouses, and
hospitals, corrected, as they have too often
been, by the ghastly hand of Death himself,
have fixed the limits of the food necessary for
health, with an accuracy which, considering
the price of human life that has been paid
for it, ought surely to satisfy the most rigid
economist.
From such sources of information we may
deduce, that a healthy aclnlt male, of active
habits, requires daily about two pounds of
solid food. Of this food, six or eight ounces
arc, preferably, meat. While, if the quality of
such a diet be lowered (as, for example, by the
* It would not be difficult to point out, how these
views concur to explain the preference of fat as a
calorific food, by the inhabitants of cold climates.
introduction of much potatoes or rice), its
quantity ought to be proportionally raised,
so as to compensate this diminution of its
nutritious characters.
Relations of digestion to nutrition generally.
We have thus specified the various ali-
mentary substances which are normally sub-
mitted to the action of the digestive canal.
And the functions of the different segments
and structures of this tube have already, so
far as possible, been assigned to each.
All these functions, however, together
make up but a small part of the complex act
of digestion. Nay, more, digestion itself is
only a part of a still wider and more complex
process of nutrition. And, further, the rela-
tion borne by digestion to nutrition is by no
means limited to an absorption of new matter
into the body ; but also involves a revolution
or cycle of much of the existing substance of
the organism, between those acts of ingestion
and egestion, which mark the respective ex-
tremes of its nutritional life. Hence it seems
necessary to end this description of the ali-
mentary canal by a succinct enumeration of
(1st) the series of phenomena which consti-
tute the digestive act, and (2nd) the share
which digestion itself takes in nutrition
generally.
We may best review the various stages of
digestion generally, by supposing that we could
track a mass of mixed food through the whole
extent of the alimentary canal, and could
observe the changes which it gradually under-
went in this course. Such a food must of
course be assumed to consist of proper pro-
portions of all the alimentary principles, in
the states in which they are ordinarily found
in any diet suitable for the maintenance of
health in the human subject.
The entry of such a food into the mouth
would mark the end of what is generally de-
scribed by systematic writers as the first stage
of digestion: namely, the act of prehension.
The food having arrived in the cavity of
the mouth, is next subjected to the operations
of mastication and insalivation.
Of these two processes, the first effects the
mechanical division of the food : reducing
it to small particles ; increasing, therefore,
its relative surface; and hence preparing
it for the action of all those secretions to
which it is exposed in its further course
through the alimentary canal. The mechanism
of this act is greatly aided by the simultaneous
admixture of the saliva. This liquid is added
to the food in quantities that vary, according
to its dryness and the consequent need of such
an addition, from 4 (apples) to 80 (bread)
per cent, of the alimentary substance that is
undergoing mastication.
But insalivation also adds an important
chemical influence to the preceding mecha-
nical advantage. The united secretions of
the parotid, sublingual, and submaxillary
glands, and the mucous membrane of the
mouth, together furnish a liquid mixture,
which converts starch into grape sugar with
the greatest rapidity and energy. The perfect
398
STOMACH AND INTESTINE.
and instantaneous character of this change,
which is only paralleled by the similar efficacy of
the pancreatic juice, quite distinguishes it from
that slower and less perfect metamorphosis
which other animal secretions and substances
are able to produce. The absence of the high
temperature, and the evident putrefaction,
which are generally associated with the action
of these latter, still further distinguish the
specific metamorphosis due to these secretions.
But the substance and secretion of any one
of the salivary structures, seems insufficient
for the production of this agent. The sub-
maxillary glands, and the mucous membrane
of the mouth can, however, together furnish it
without any aid from the parotid.*
The mastication and insalivation of the
food is immediately followed by its deglutition,
which propels the pulpy or semifluid mass it
now forms into the stomach.
On entering this organ, it is subjected to a
special act of gastric digestion.
The energetic action of the mixed saliva
is not affected by the gastric juice secreted by
the stomach. Much of the starch of the food
is probably converted into sugar during the
short sojourn of the aliment in this cavity.
The sugar thus produced would seem to be
absorbed by the vessels of the gastric mucous
membrane with extraordinary rapidity. The
water, salts, and soluble organic compounds
of the food are similarly taken up. And the
gastric juice attacks and dissolves the pro-
tinous element of the food. The perfect-
ness of this process of solution depends on
the mechanical state of the substances con-
cerned, and the quantity and efficiency of the
active liquid. Of the resulting solution or
peptone, part is immediately absorbed by the
gastric vessels, while part passes on into the
duodenum, in company with portions of pro-
tein, which have not yet yielded to the solvent
process. Many of these portions ultimately
become dissolved, and with the peptone that
accompanies them, are taken up by the veins
of the intestine.
The intestinal digestion of the food is a still
more complex act. The chyme that enters
the duodenum probably contains all the
alimentary principles originally present in the
food. But it includes them in very different
proportions compared with their original
quantities. And these proportions have very
diverse destinies in connection with the di-
gestive process.
The watery ingredient of the food, and the
salts it introduces, probably have but to
complete their absorption. The soluble cal-
careous compounds appear, however, to de-
compose the bile ; and to combine with and
precipitate some of its acids in the shape of
insoluble salts of lime.
* The experiment on which Bidder and Schmidt
(0/J. cit. p. 281) claim a similar efficacy for that of
the mucous membrane of the small intestine, appears
scarcely to warrant such a conclusion. Should its
accuracy be hereafter established, it would be inte-
resting to determine how far the glands of Brunn
were concerned in the process.
The protein-compounds probably continue
their course through the intestine, still un-
dergoing (or rather completing) a gradual
process of solution under the action of the
gastric juice which accompanies them.
Whether any special intestinal juice* aids
this process, may at present be looked on as
doubtful. And whether the quantity of bile
usually added in the duodenum can really
hinder it, in the way in which Bidder and
Schmidt f have found that it suspends the
power of the gastric juice out of the body,
remains equally uncertain.
The starch of the chyme would seem to
be converted into sugar, by the addition of a
further quantity of an agent, similar to that
which is furnished by the mixed secretions of
the salivary glands and mouth. At any rate, the
secretion of the pancreas, which is poured
out into the duodenum with the bile, is gifted
with the capacity of inducing this change just
as rapidly as the mixed saliva itself.
The fatty constituents of the food are
probably absorbed by two channels, if not by
two processes. But the quantitative share
taken by each of these, remains at present
unknown. That a certain portion of the fat
contained in the food is taken up by the
vessels of the alimentary canal, seems evident
from the remarkable difference in the amount
of this substance, which is found in the organic
residuum of the portal blood, and that of the
ordinary systemic veins. | But the quantity
thus absorbed can scarcely be large. It ap-
pears to consist chiefly of the more fluid
elain. And hence there seem no valid grounds
for the supposition of much assistance being
given to its transudation from the digestive
canal into the veins, by means of a saponi-
fication with their alkaline blood. A much
greater quantity of the fatty matter of the
food is taken up by the lacteals of the villi,
and is conveyed from these vessels into the
thoracic duct. The microscopic details of
this process have already been mentioned.
Hence, it only remains for us to notice its
chemical relations to the various secretions
poured into the small intestine, in the lacteals
of which segment of the canal the white or
fatty chyle is chiefly found.
The experiments and observations of
Claude Bernard would ascribe the formation
of chyle chiefly to the pancreatic juice. This
secretion appears to have the power of se-
parating fats into their acid and base. But
the fact, that such a saponification is pre-
vented by an admixture of gastric juice, or
any other acid, would justify us in doubting
whether the change really occurs in the
acid chyme of the living body. And all the
appearances of the chyle in the lacteals of the
villi concur in representing their fatty contents
as being not saponified, but merely in a state of
minute division. The production of this con-
dition, which closely corresponds to that of
* Compare p. 349.
t Loc.cit.
j See Heller's Archiv. vol. iii. p. 487. ; vol. iv.
pp. 1537. 97132.
STOMACH AND INTESTINE.
399
oily substances when reduced to an artificial
emulsion, would seem to be one of the chief
offices of the pancreatic juice.
The evidence adduced by Bernard* in sup-
port of his views appears very conclusive.
His experiments gave him the means of ob-
taining large quantities of pancreatic juice
from Dogs. A mixture of this secretion and
oil, when shaken together, immediately pro-
duced an emulsion of the most intimate kind,
such as no other animal fluid which he exa-
mined could imitate. A similar emulsion
within the body could be seen in the Rabbit,
when fed on butter. In this animal, the pan-
creatic duct opens into the intestine com-
paratively low down. And hence there is,
under such circumstances, a long extent of
bowel above the orifice of this duct, quite
devoid of white chyle ; while below, the lac-
teals are distended with this fluid. And,
finally, experiments on the healthy animal f,
and observations on human disease, tend to
establish the same conclusion. Complete
artificial obstruction of the pancreatic duct,
diversion of its contents from the intestine,
and extensive disease of the secretory struc-
ture of the gland, alike prevent the forma-
tion of white chyle.
The small quantity of the pancreatic se-
cretion would, perhaps, indicate that much
of the metamorphosis of starch is effected by
the saliva. And, taken in conjunction with
the neutral or feebly alkaline reaction of the
bile, and the apparently small amount of alka-
line intestinal juice, it may at any rate be re-
garded as throwing great doubt upon the old
theory of a direct neutralization of the acid
chyme in the intestinal cavity.
The precise share taken by the bile in the
process of intestinal digestion, is even more
obscure than that of the pancreatic fluid.
It may probably be stated as follows :
The bile is not essential to the solution or
absorption of any one of the alimentary prin-
ciples. Nor, on the other hand, does its pre-
sence check the conversion of protein into
peptone J, or of starch into sugar. But from
the appearance of the faeces in jaundice and
biliary fistulae, it would seem that its admix-
ture with the food limits and modifies the
* In a mere enumeration of the chief digestive
changes, all controversial discussion would be out
of place. I shall therefore content myself with
saying, that having seen this eminent physiologist
perform ihe more essential of his admirable ex-
periments abroad, and repeated some of them at
home, I entertain little doubt of their substantial
accuracy. And to the ordinary disparity between
the value of the negative and positive results of
experiment, one may add, that none of Bernard's
German antagonists appear to have succeeded in
procuring large quantities of the pure secretion.
Indeed I think that a detailed criticism of these
negative results themselves, would amply justify
the retention (for the present) of Bernard's view.
t The inflammation which sometimes follows
these experiments on animals, may hinder the ab-
sorption of fat in two ways : either by attacking
the substance of the pancreas, or by engaging the
tissues of the villi themselves.
J Compare p. 349., on the action of the intestinal
juice.
putrefaction of its animal constituent, and
the acid fermentation of its vegetable por-
tions; and thus far aids in its proper assimi-
lation. While the constipation generally ob-
served in such cases, indicates that the bile
is also a stimulus to the muscular action of
the bowels.
The absorption of fatty matter is, however,
materially influenced by the bile. So that,
when this secretion is altogether diverted
from its accustomed channel, its absence from
the intestinal canal reduces the quantity of
fat taken up here to about one-fourth of that
normally absorbed.
The quantity of biliary solids discharged
with the faeces is but a very small fraction of
that poured into the bowel ; probably not
more than T ^th or T V n - And much of this
may be regarded as a precipitate ; which is
produced, partly by an oxidation of a small
part of the biliary fats into resinous matter,
and partly by the combination of the fatty
acids of the bile with the lime taken in the
food.
The details of the assistance given by the
bile to digestion, are very obscure. But as-
suming the accuracy of M. Bernard's views
with respect to the pancreatic function, we
may conjecture, that it is the venous, rather
than the lacteal absorption of fat, which is
furthered by the hepatic secretion. This view-
agrees with the known capacity of the soda
in the bile to unite with fatty acids in the
form of a soap. And that separation of the
neutral fats of the food into acid and base,
which would probably precede such a sapo-