586 
EXPERIMENTS ON DIGESTION. 
which we have examined that have a gall-bladder, we have found 
this vessel almost empty during the process of digestion, and tho- 
roughly filled when the animal was fasting. It is also probable 
that the pancreatic juice flows in a much greater quantity into 
the intestinal canal during digestion, than when the animal is 
fasting. 
The chyle and the bile, which pour themselves into the duode- 
num, act on its mucous membrane as a stimulus to increase the 
secretion of the intestinal fluids, of the proper mucous fluid, and 
of the aqueous fluid of less consistence. The mucus presents itself 
under the form of large white or greyish white flocculi, which are 
incontestably the product of the secretion of the glands of Brunner 
and Peyer. 
During digestion the peristaltic motion of the intestinal canal is 
quickened and strengthened. We have seen one part of the intes- 
tine shorten and close itself, while another part was distended and 
elongated. These movements are effected by the contractions and 
dilatations of the small intestines, in consequence of the irritation 
which the chyme and the bile poured into the canal produce upon it. 
The contents of the duodenum and of the first portion of the 
small intestines are always acid. The acidity gradually diminishes 
in the second portion, and ordinarily disappears altogether at the 
extremity of this viscus. In general the acidity prevails in propor- 
tion as the food is difficult to digest. The free acid that is met 
with in the small intestines is chiefly the acetic acid. It is possi- 
ble that a little free butyric acid may sometimes mingle with this. 
Hydrochloric acid is seldom met with in the small intestine, for or- 
dinarily the filtered fluids of this organ yield by incineration an 
alkaline carbonate, a salt that could not have been formed if the 
hydrochloric acid had existed in any appreciable quantity. 
The acid chyme which passes into the small intestine mingles 
with the bile, the pancreatic juice, and the fluids secreted as well 
by the mucous membrane as by the glands of the intestine. The 
bile, in virtue of the irritation which it exercises on the small in- 
testines, at the same time increases the intestinal fluids, and accele- 
rates the peristaltic motion. Mingling with the dissolved aliments, 
it imparts to them a yellow colour, which changes to various shades 
of brown before it reaches the rectum. Beside this, it produces 
the following changes in the chyme : — 
1. The hydrochloric acid of the chyme, which is derived from 
the gastric juice, unites itself with the soda contained in the bile, 
or that alkali was hitherto combined with the carbonic and acetic 
acids. The disengaged carbonic acid, of which, in truth, the 
quantity ought to be very small, is probably one of the causes 
which produce the minute bubbles of gas that are almost 
