^fn. 
PHYSIOLOGY. 
jiience, according to Lieberkuhn and other 
microscopical observers, by patulous orifices 
on the surface of the villi. The latter pro- 
jections, so named from a comparison with 
the pill of velvet, are very numerous on the 
circular projecting folds of the internal coat, 
called valvulae conniventes. These latter 
not only render the progress of the chyle 
slower, but increase very greatly the ab- 
sorbing surface, and penetrate, in conse- 
quence of the intestinal contractions, into the 
midst of the chyle in quest of its nutritive 
particles. A fluid is secreted from the in- 
testine, analogous to that furnished by the 
stomach, although an accurate examination 
of its nature and properties is one of the 
physiological desiderata, (succus intestina- 
lis). At the same time that the absorption 
of the chyle from the villous surface of the 
intestine is going on, it is moved gradually 
downwards towards the large intestine by 
the peristaltic motion. This is an undula- 
tory and gentle constriction, taking place 
in several parts of the tube at once, and 
producing therefore a singular appearance, 
compared to the crawling of worms, and 
hence termed vermicular. It moves the 
chyle repeatedly over the surface of the in- 
testine j and though it must urge that fluid 
partially upwards, yet its chief effect in the 
healthy state is exerted in the opposite di- 
rection. It is chiefly in disease that an 
antiperistaltic movement occurs, which con- 
veys bile into the stomach, and even the 
whole contents of the small and large intes- 
tine. 
By the powers now explained, which 
propel the alimentary mass by their con- 
tractions, and by the admixture of tlie vari- 
ous fluid menstrua which dilute and alter 
its properties, those memorable changes are 
effected by which our food is said to be 
. animalized or assimilated. In the duode- 
num and upper part of the jejunum it forms 
an equably mixed fluid, of the consistence 
of thick cream, greyish, and rather acid. 
Lower down it separates into two parts ; 
the excrementitious of a pale brown or yel- 
low colour, and nauseating smell ; and the 
true chyle, separated from the former by 
the bile, and swimming on its surface. 
Action of the large Intestine, The excre- 
mentitious portion of the chyme, deprived 
almost entirely of every nutritive portion, 
enters the caecnm; its passage through the 
last part of the ileum being favoured by a 
copious secretion of mucous from the glands 
which abound in that part. The valvula 
eoli, which is the boundary between the 
large and small intestines, is designed to 
prevent the contents of the former from re. 
gurgitating into the latter : and it performs 
this office in general ; for nutritive clysters 
would otherwise enter the small intestines, 
and thus enable us to administer food 
enough for the support of life per anum : 
yet it occasionally fails in its office : hence 
vomiting of feces, and of tobacco clysters. 
The large intestine may be regarded as 
the organ in which the residue of the chyme 
' undergoes its last change ; viz. the conver- 
sion into feces; as a reservoir, protecting 
us from the disgusting necessity of having 
that residue constantly flowing off ; and as 
the instrument of its final expulsion from 
the body. 
Some absorbents exist in this last part of 
the alimentary tube, and convey what nu- 
tritive parts still remain in the intestinal 
cdntents ; but they are comparatively few, 
and hence the impossibility of nourishing 
the body by way of clyster. 
The conversion of the alimentary residue 
into feces is owing to some active opera- 
tion of the intestine ; as these are very dif- 
ferent from the mere putrid remains of 
animal or vegetable matter. And when 
this operation is deficient, portions of the 
food are seen in the evacuations per anum 
but slightly changed. The fecal matter is 
conveyed onwards by the peristaltic motion 
of the large intestine ; it becomes thicker 
and more consistent in its progress, and is 
usually formed more or less decidedly by 
the cells of the colon. Its natural consis- 
tence is just sufficient to retain these fnarks; 
and its appearance throughout should be 
homogeneous. The colour depends on the 
admixture of bile, and in the most natural 
state is of a yellow brown. Although the 
change which reduces the residue of our food 
to feces is so far from being mere putrefac- 
. tion, that the excrement is in fact less 
prone to putrefy than other animal matter ; 
yet there is, as in putrefaction, a disengage, 
ment of gaseous products, particularly of 
sulphurated hydrogen. The colouring mat- 
ter of vegetables is often seen in the feces, 
as the green of spinach, and red of beet 
root; and the fibrous indigestible parts 
of vegetables, as the skin of fruits, husk of 
grain, &c. The latter, indeed, is so little 
affected by the powers of digestion, that 
when the covering is entire, a grain may 
pass through the body, and still retain the 
power to germinate. 
The expulsion of the feces takes place 
when they arrive in the rectum, which is 
