THE MAMMALIA— MAN AND BEASTS. 
69 
only from thrco to five times their length among the Carnivora. In omnivorous 
animals, such as Man, its length is intermediate to these, being six or seven times that 
of the body. 
Several experiments have been made by Sir Astley Cooper to ascertain the diges- 
tive power of the Dog. He found that this animal digested pork more easily than 
mutton, the latter moro rapidly than veal, and beef with greater difficulty than any 
of the othcr.s. lie found that fish and cheese were easily digested by the Dog, and 
boiled veal more readily than roast. The fat of meat seemed more digestible than 
cheese, codfish dissolved more readily than beef, and boef than potato. The order 
of digestion for the different parts of the same kind of animal food, was fat, muscle, 
skin, cartilago, tendon, and bone, the last being the least digestible. 
Young Dogs, when they have acquired strength, and are in good health, can 
digest bones; and what is remarkable, Spallanzani has observed that the gastric juice 
of their stomachs made an impression even upon the enamel of teeth. Hoerhaavo 
asserts the contrary, but the observations of Spallanzani have been confirmed. This 
power of dissolving bono is not peculiar to the Mammalia, but is also possessed by 
some animals of the other classes. Thus the Falcons, Eagles, and Crows, usually 
refuse bones; but when introduced into their stomachs, with proper precautions, 
these refractory substances are digested. Serpents and Adders also digest them, as 
has been remarked by Spallanzani. Only the smaller bones, however, possessing the 
least solidity, arc di.ssolvod entirely and rapidly ; the harder bones require to be 
minutely divided in order to be softened and dissolved, otherwise they merely undergo 
a small loss of substance. It must be observed, that before digesting they pass into 
a cartilaginous state, and resemble indurated gelatine, as if they hatl been submitted 
to the action of nitric acid. 
The Ruminantia, like the granivorous Birds, can digest herbs and grains, only 
when these substances have been previously divided, mashed, or ground. When 
entire herbs and solid grains are introduced into their stomachs, whether uncovered, 
or inclosed in linen, or perforated tubes, these substances undergo no digestion; they 
are merely moistened or softened, and this is the extent of their modification. The 
tame result is obtained oven when they are moistened with saliva. On the contrary, 
*f bags or tubes of mashed herbs or grains be introduced into the stomachs of the 
Ruminants, the digestion is then performed in a few hours. These experiments have 
been made upon Oxen, Sheep, and many other Ruminantia, and they present similar 
results for all this order of Mammalia, They have also been made upon the Horse, 
and with the same result, although ho does not ruminate. 
Many physiologists have attempted, with various success, to effect artificial diges- 
tions out of the body, by extracting the gastric juices from the stomachs of different 
animals, and afterwards mixing them with the food. Spallanzani, by these experi- 
ments with the gastric juices of different animals, obtained several important results, 
^hen cold, the gastric juice produced scarcely any effect ; it merely opposed putrefac- 
tion, but did not exercise its dissolving and digestive power until it was raised to its 
proper temperature. It did not act upon grains and herbs until they were ground, 
niashed, and impregnated with saliva. The gastric juice of Man softened and seemed 
to digest beef in about thirty-six hours, when raised to a temperature equal to that 
of the stomach. He also observed, that the gastric juice of one species often acted 
opon a great variety of substances, and yet it did not always act upon substances 
^hieh could be dissolved by the gastric juice of another species. 
From these instances of artificial digestion, wc may readily expect that the stomach, 
being lubricated by the gastric juice, will continue to digest after the death of the 
and even it lias been said to digest itself. Hunter first noticed the fact, that 
the gastric juice will act upon the sides of the stomach after death, and to this cause 
attributed the erosions and perforations which are somcliraes found in the stomachs 
human subjects. Spallanzani made several experiments upon Dogs and Cats with 
a similar result. Ho caused the animals intended for trial to fast for a long time, 
and then to be fed immediately before being killed. Their bodies wore placed in 
stoves which preserved their natural temperature, and in the course of a few hours 
found that the food in their stomachs was sensibly digested. 
The chyme, after being slowly formed on the surface of that alimentary mass which 
stomach contains, accumulates as it forma near the pylorus or intestinal opening 
the stomach. It is raised from this situation into tlie narrow pyloric entrance, by 
increased action of those gentle and almost insensible contractions which it had 
already experienced. Tho more violent contractions which are necessary to expel the 
phyme from the cavity of the stomach, usually originate in the duodenum or small 
•^testine, from which they are transmitted to the pylorus, and thence gradually to the 
®>^tiro stomach. But this ascending movement of the chyme, during which some 
P<J*’sons experience much uneasiness, is immediately converted into another movement 
^ the opposite direction; and it is by means of this reaction that the chyme finally 
Tk'^****^* pylorus, which is opened for that pui*posc, and by the same cause, 
ho movement is repeated, and continues as often as the quantity of chyme newly 
oi'med in the stomach requires to >0 removed. In this way, the duodenum is gra- 
ualiy each operation by the food chymified in the stomach. 
^ terwards the course of the chyme is very slo^y in the intestines, and the same ob- 
ervation ajiplies to the intestinal movemcuis generally, c.xcept when excited by 
or mental emotion. 
*^l>o fithm.s of the tluodemtm favors the ! 
! secretion of the hilo and pancreatic juices 
the T *"■ juices. All these now fluids being mixed with 
0 cliyrao immediately cliange its nature. It almost wholly loses its acidity : its 
eoioaj. e' — - ■■ ... ^ ’ 
ness 
>• changes from gray to yellow, and it becomes bitter to the taste. This hitter- 
^ U> some animals extends oven to the stoinachio product itself, especially in 
If tl punotrates through the pyloric entrance into the stomach, 
witl ^ contain fat or oily matters, those substances pass into the intestine 
fhem"**^ undergone any alteration in the stomach, but the bile uniting with 
»ndtl "I'inl' is easily dissolved. With the exception of herbs, 
iuis n't*° sultstances, the duodenum permits all bodies, which the stomach 
similar digested, to pass without altertition. The same aliments produce a 
'ho h ° ‘“uu'nls of the same species when in health, and the changes which 
yme afterwards undergoes are equally the same. But the chyme produced 
18 
from animal food is thicker and more viscous than that produced from vegetables ; 
it is reddish, aud docs not curdle milk. Vegetable chyme, on the contrary, is al- 
most fluid ; it has a yellowish tinge, and curdles milk. Further, the chyme fur- 
nished by vegetables is less rich in nutritious matter, and it wants that albuminous 
substance, which is found in chyme resulting from animal food. Different kinds of 
gas are disengaged during the process, hut their nature varies according to the species 
of animal, its ago and state of health, the kind of food which is used, and especially 
according to the part of the intestinal canal from which they proceed. 
In a short time after the chyme has descended into the duodenum, and undergone 
the action of the bile, it divides into two parts. The one is a fluid termed c/iyle, 
which is the part destined to nourish tlie animal ; the other is more solid and coarse, 
and less homogeneous, and, being the useless residue of the aliment, is finally re- 
jected. 
This separation of the chyle, and even its formation, appear to he more especially 
due to the influence of the bile ; at least it is certain that digestion is always im- 
perfect, and that the chyle is either deficient or in small quantity, when the bile can- 
not mix with the chyme prepared by the stomach. 
-Vmong the greater part of the Mammalia, the time which the chyle takes to form, 
after the chyme has passed from the stomach into the duodenum, varies from two to 
four hours. This function is much slower among the Fishes, and still more so with 
the Reptiles. Well formed chyle has sometimes boon found in the white vessels which 
adjoin the stomach, and it Ijas been said in consequence, that the stomach can form 
chyle. But this has only been scon in certain animals, whoso bile frequently mingles 
with the gastric juice. The Dog appears to be an instance ; but it does not seem to 
be of frequent occurrence among the Mammalia generally. 
“ Les cxcremciis,” observes M. Isidore Bourdon, “ scparcs dn chyle qui les sur- 
nago ct dont 1‘absorption s’op&re dans le haut de I’intestin, perdent peu-a-pcu, I'l me- 
sure qu'ils dcscondent vers les gros intestins', la fluidite qu’ils avjiiont dans le milieu do 
I’intestin grCle. Le mucus des gros intestins cn feivorise la marche vers I’aiius, mais 
les leges que prese.ntent ces conduits do distance cn distance, cn prolongcnt le sejonr 
ot en accroissent la consislance. O est par 1 action des fibres musculeuses des intes- 
tins que les excremens son peu-4-pcu pousscs vers I’anus, et e’est par les muscles ab- 
dominaux qu’ils sent finaletncnt rejeles hors du corps. Cette expulsion resulte d’un 
mecanisme assez complique on la glotte, an moins chez les Mamif^res, jouo un role 
important. Le rejet des maticres fccales est bcaucoup pins facile chez les animaux 
ovipares et dans rOrnithorrhynque ; ct ce'.te difference resulte de ce quo ces animaux 
ayant un cloaquc, leurs urines s’amassont dans ce lien aussi bicn quo les excremens ; 
qu’elles dolayent. Les cxeremeiis diffiiront pour chaqne espiice d’animal ; mais la 
plu.5 grande difference s’ohservo surtout ontro les carnivores ct les herbivores. Le 
meme animal, s’il est omnivore, a des excremens tris differens, siiirant qn’il use 
d alimens vegetanx on d'alimens tiros do I’autro r6gnc. Les excremens provenant 
d’uuo nourriturc animale ont la propriele do fairc caillor le lait, et il n’e.xiste rien de 
semblable pour les feebs des alimens vegotaux. Cost absolument le contraire de ce 
quo nous avons dit pour le chyme des caniivores et dcs herbivores.” 
Bordeu has made several intorcstiiig remarks on this subject; the curiosity of an 
ingenious mind having overcome the natural disgust towards a study so repulsive. 
The researches of Prout are more precise than those of Borden. 
Complicated fluids are digested as well as solids, but a large part of them are ab- 
sorbed directly by the stomach. Water, alcohol, and other simple fluids, contribute 
towards nutrition, chiefly by Imparting their fluidity to some of the animal bodies. 
Those movements of the intestines by means of which they are traversed by the 
stomachic product, are termed pcristullic. There are, however, other movements, 
which are directed from below, upwards, in the contrary direction, and are hence 
termed anti-peristaltic. These movements produce various phenomena, such as Re- 
gurgitation, Rumination, and Vomiting. Among the Mammalia no animal vomits 
more readily than the Cat; there arc, however, few Vertebrated animals which do 
not possess the power of vomiting. The Horse cannot vomit in ordinary eases, be- 
cause the situation of the eardia opposes an obstacle to the return of the food towards 
the msophagns. 
It is ascertained that the chyle separates itself from the alimentary mass, after it 
has remained for some time in the distended cavity of the duodenum, and that in 
a short time the hilo and panercatio juices act upon it, although we arc ignorjint of 
the precise nature of the operation. With respect to tho characters and quality of 
the chyle, this substance is very plentiful in the Mammalia alone. Tho chyle 15 
always of an opaque white, which has caused it to be compared to milk. When 
taken from the body, and left to itself, it separates into two portions ; the one is 
serous and saline, while tlie other is fibrous, in this respect nearly rcserablinn- the 
blood when similarly treated. If placed in an inert vessel, the chyle usually acquires 
a reddish tinge, which appears to bo owing to the action of tho oxygen in tho air ; 
and a thick kind of cream forms on the surface. This resemblance of tho chyme to 
milk 1ms led some physiologists to consider the one as the product of tho other. One 
thing is certain, that nothing tends more towards the abundant secretion of miik, in 
the female, than lliat plentiful production of chyle resulting from the abundant sup- 
ply of nutritious food. In other respects, the nature of the food with which the ani- 
mal is nourished greatly influences the chyle resulting from digestion. Different 
.substances do not produce the same kind of chyle; fat matters produce a chyle which 
is white, and more opaque than that yielded by substances which are not fat. Tiie 
chyme never acquires the hue of any colouring matter which may have been intro- 
duced into the intestine ; and it is even with difficulty that it can be made to acquire 
an odour. 
The chyle, wrheu once separated from the chyme, of which it may bo regarded as 
tho extract, flo.its on the surface of this matter, and accumulates by small rivulets in 
tho mucous valvules, with which tho interior of tho smaller intestines are supplied. It 
remains in this place for a few instants, when it is absorbed by the small vessels, 
which servo to bring it into the mass of tho blood. It is impossible to say in precisely 
what manner, or by what force or mechanism, this absorption of the chyle is effected, 
and to indulge in conjecture would but lead to certain error. On carefully examining, 
with tlie naked eye, the interior cf the intestine, at the moment when tho chyle is 
