HOW ANIMALS DIGEST. 93 
animals lias no other office, so far as we know, than to 
moisten the food for swallowing. 
Taking Man as an example, let us note the main facts 
in the process. During mastication, by which the relative 
surface is increased, the food is mixed with saliva, which 
moistens the food, 48 and turns a small part of the starch into 
grape-sugar. Passed into the stomach, the food meets the 
gastric juice. This is acid, and, first, stops the action of 
the saliva ; secondly, by means of th e pepsin which it con¬ 
tains, and the acid, it dissolves the albumen, fibrin, and such 
constituents of the food. This solution of albuminoids 
is called a peptone , and is especially distinguished from 
other such solutions by its diffusibility— i. e ., the ease with 
which it passes through a membrane. Some of these pep¬ 
tones, with the sugars of the food, whether original or the 
product of the action of the saliva, are absorbed from the 
stomach. The food, while in the stomach, is kept in con¬ 
tinual motion, and, after a time, is discharged in gushes 
into the intestine. The'name chyme is given to the pulpy 
mass of food in the stomach. 49 In the intestine the chyme 
meets three fluids—bile, pancreatio juice, and intestinal 
juice. All of these are alkaline, and at once give the acid 
ch} 7 me an alkaline reaction. This change permits the 
action of the saliva to recom¬ 
mence, which is aided by the 
pancreatic and intestinal juices. 
The pancreatic juice has much 
more important functions. It 
changes albuminoid food into 
peptones, and probably breaks 
up the fats into very small par¬ 
ticles, which are suspended in 
the fluid chyle. This forms an Fig. 59.—Chyle Corpuscles, X 500. 
emulsion , like milk, and causes the chyle to appear whit¬ 
ish. The bile has important functions, but little under- 
