DIGESTION. 
*ew changes. ’The stomach is a strong soft 
bag. of Efferent forms in different animals : 
in man it has some resemblance to the bag oi 
n bagpipe. In this organ the food is con- 
verted into a soft pap, which has no resem- 
blance to the food when first introduced. 
This pap has been called chyme. 
Since chyme possesses new properties, it 
is evident that: the food has undergone some 
changes in the stomach, and that the ingre- 
dients of which it was composed have entered 
into new combinations. 
The formation of chyme, in fact, is owing 
to the stomach ; and it has been concluded, 
from the experiments of Stevens, '•■•Reaumur, 
Spallanzani, Scopoli, Brugnatelli, Carimini, 
&c. that its formation is brought about by 
the action of a particular liquid secreted by 
the stomach, and for that reason called gastric 
juice. 
That it is owing to the action of a liquid is 
evident ; because, if pieces of food are in- 
closed in close tubes, they pass through the 
stomach without any fartlu'r alteration than 
would have taken place at tire same tempera- 
ture out of the body; but if the tubes are 
perforated with small holes, the food is con- 
verted into chyme. 
This liquid does not act indiscriminately 
upon all substances : for if grains of corn are 
put into a perforated tube, and a granivorous 
bird is made to swallow it, the com will re- 
main the usual time in the stomach without 
alteration ; whereas, if the husk ol the grain 
is previously taken oil, the whole of it will be 
converted into chyme. It is well known, too, 
that many substances pass unaltered through 
the intestines of animals, and consequently 
are not acted upon by the gastric juice. This 
is the case frequently with grains of oats when 
they have been swallowed by horses entire 
with their husks on. This is the case also 
with the seeds of apples, &c. when swallowed 
entire by man ; yet these very substances, if 
they have been previously ground sufficiently 
by the teeth, are digested. It appears, there- 
fore, that it is chiefly the husk or outside of 
these substances which resists the action of 
the gastric juice. Wc see also, that tritura- 
tion greatly facilitates the conversion of food 
•into chyme. 
The ’ gastric juice is not the same in all 
animals ; for many animals cannot digest the 
food bn which others live. The conium nra- 
culatum (hemlock), for instance, is a poison 
to man instead of food, yet the goat often 
feeds upon it. Many animals, as sheep, live 
wholly upon vegetables ; and if they are made 
to feed on animals, their stomachs will not 
cjigest them: others again, as the eagle, feed 
wholly on animal substances, and cannot 
• digest vegetables. 
The gastric juice does not continue always 
•of the same nature, even in the same animal: 
it, changes gradually according to circum- 
stances. Graminivorous animals may be 
•brought to live on animal food ; and after 
they have been accustomed to this for some 
time, their stomachs become incapable of 
digesting vegetables. On the other hand, 
t hose animals which naturally digest nothing 
but animal food may -be brought to digest 
vegetables. 
What is the nature of the gastric juice, 
which possesses these singular properties? 
It is evidently different in different animals ; 
, in it it is a very difficult .task, if not an ini- 
VOL. I. 
possible one, to obtain it in a state of purity. 
Various attempts have indeed been made by 
very ingenious philosophers to procure it ; 
but their analysis of it is sufficient to shew 
us, that they have never obtained it in a state 
of purity. 
The ’methods which have been used to 
procure gastric juice are, first, to kill the 
animal whose gastric juice is to he examined, 
after it iias fasted for some time. By this 
method Spallanzani collected 37 spoonfuls 
from the two first stomachs of a sheep. It 
was of a green colour, undoubtedly owing 
to the grass which the animal had eaten. He 
found also half a spoonful in the stomach of 
some young crows which he killed before they 
had left their nest. 
Small tubes of metal pierced with holes, 
and containing a dry sponge, have been 
swallowed by animals ; and when vomited up, 
the liquid imbibed by the sponge is squeezed 
out. By this method, Spallanzani collected 
481 grains of gastric juice from the stomachs 
of live crows. 
A third method consists in exciting vomit- 
ing in the morning, when the stomach is 
without food. Spallanzani tried this method 
twice upon himself, and collected. one of the 
times, 1 oz. 32gr. of liquid; but the pain 
was so great, that he did not think proper to 
try the experiment a third time. Mr. Gosse, 
however, who could excite vomiting when- 
ever he thought proper, by swallowing air, 
has employed that method to collect gastric 
juice. 
Spallanzani has observed that eagles throw 
up every morning a quantity of liquid, which 
he considers as gastric juice ; and he has 
availed himself of this to collect it in con- 
siderable quantities. 
It is almost unnecessary to remark how im- 
perfect these different methods are, and how 
far every conclusion drawn from the exami- 
nation of such juices must deviate from the 
truth. It is impossible that the gastric juice, 
obtained by any one of these processes, can 
be pure ; because in the stomach it must he 
constantly mixed with large quantities of 
saliva, mucus, bile, food, &c. It may be 
questioned, indeed, whether any gastric juice 
at all can be obtained by these methods ; for 
as the intention of the gastric juice is to con- 
vert the food into chyme, in all probability it 
is only secreted, or at least thrown into, the 
stomach, when food is present. 
We need not be surprised, then, at the 
contradictory accounts concerning its nature, 
given us by those philosophers who have at- 
tempted to examine it; as these relate not so 
much to the gastric juice, as to the different 
substances found in the stomach. The idea 
that the gastric juice can be obtained by 
vomiting, or that it is thrown up sponta- 
neously by some animals, is, to say the least 
•of it, very far from being probable. 
According to Brugnatelli, the gastric juice 
of carnivorous animals, as hawks, kites, &c. 
has an acid and resinous odour, is very bitter, 
and not at all watery ; and is composed of an 
uncombined acid, a resin, an animal sub- 
stance, and a small quantity of muriat of soda. 
The gastric juice of herbivorous animals, on 
the contrary, as goats, sheep, & c. is very 
watery, a little muddy, has a bitter saltish 
taste, and contains ammonia, an animal ex- 
tract, and a pretty large quantity of muriat of 
soda. Mr. Canninati found the same in- 
3 vU 
gredients ; but he supposes that Hie ammonia 
had been formed by the putrefaction of a part 
of their food, and that in reality the gastric 
juice of these animals is of an acid nature, 
The accounts which have been given of the 
gastric juice of man are so various, that it is 
not worth while to transcribe them. Some- 
times it has been found of an acid nature, at 
other times not. The experiments of Spa!-, 
lanzani are sufficient to shew, that this acidity 
is not owing to the gastric juice, but to the 
food, lie never found any acidity in the 
gastric juice of birds of prey, nor of serpents, 
frogs, and fishes. Crows gave an acidulous 
gastric juice only when fed on grain ; and he 
found that the same observation holds with 
respect to dogs, herbivorous animals, and 
domestic fowls. Carnivorous birds threw up 
pieces of shells and coral without alteration ; 
but these substances were sensibly diminished 
in the stomachs of hens, even when inclosed 
in perforated tubes. Spallanzani himself 
swallowed calcareous substances inclosed in 
tubes-; and when he fed on vegetables and 
fruits, they were sometimes altered and a 
little diminished in weight, just as if they had 
been put into weak vinegar ; but when he 
used only animal food, they came out un- 
touched. According to this philosopher, 
whose experiments have been by far the most 
numerous, the gastric juice is naturally neither 
acid nor alkaline. When poured on the 
carbonat of potass, it causes no effervescence. 
Such are the results of the experiments on 
the juices taken from the stomach of animals. 
No conclusion can be drawn from them 
respecting the nature of the gastric juice. 
But from the experiments which have been 
made on the digestion of the stomach, espe- 
cially by Spallanzani, the following facts are 
established. 
The gastric juice attacks the surface of 
bodies, unites to the particles of them, which 
it carries off, and cannot be separated from 
them by filtration. It operates with more 
energy and rapidity the more the food is 
divided, and its action is increased by a warm 
temperature. The food is not merely reduced 
to very minute parts ; its taste and smell are 
quite changed; its sensible properties are 
destroyed, and it acquires new and very dif- 
ferent ones. This juice does not act as a 
ferment ; so far from it that it is a powerful 
antiseptic, and even restores flesh already 
putrefied. There is not the ^smallest appear- 
ance of such a process ; indeed, when the 
juice is renewed frequency, as in the stomac h, 
substances, dissolve in it with a rapidity which 
excludes all idea of fermentation. Only a 
few air-bubbles make their escape, which ad- 
here to the alimentary matter, and buoy it up 
to the top, and which are probably extricated 
by the heat of the solution. 
With respect to the substances contained 
in the stomach, only two facts have been per- 
fectly ascertained. The first is, that the 
juice contained in the stomachs of oxen, 
calves, and sheep, invariably contains -nn com- 
bined phosphoric acid, as Macquart and Vau- 
quelin have demonstrated : the second, that 
the juice contained in the stomach, and even 
tire inner coat of the stomach itself, has the 
property of -coagulating miikand tire serum of 
Wood. Dr. Young found, that seven grain’s 
of the inner coat of a calf’s stomach, infused 
in water, gave a liquid which coagulated more 
than 100 ounces of milk.; that is, more than 
