356 ANIMAL PHYSIOLOGY. 
become peptone, and in some animals fat is split up into free 
fatty acid and glycerine; but the digestion of fat in the stom- 
ach is very limited at best, and probably does not go on to 
emulsification or saponification. The digestion of starch con- 
tinues in the stomach until the reaction of the food-mass be- 
comes acid. This in the hog may not be far from one to two 
hours, and the amylolytic ferment acts with great rapidity even 
without the body. The food is moved about to a certain ex- 
tent, so as to expose every part freely to the mucous mem- 
brane and its secretions. It is likely that the sugar resulting 
from the digestion of starch, the peptones, and, to some ex- 
tent, the fat formed (if any), is received into the blood from 
the stomach. 
As the partially digested mass (chyme) is passed on into the 
intestine as a result of the action of the alkaline bile, the para- 
peptone, pepsin, and bile-salts are deposited. Certain of the 
constituents of digestion are thus delayed, a portion of the pep- 
sin is probably absorbed, either altered or unaltered, and pep- 
sin is thus got rid of, making the way clear, so to speak, for 
the action of trypsin. At all events, digestion in one part of 
the tract is antagonized by digestion in another, but we must 
also add supplemented. 
The fat, which had been but little altered, is emulsified by 
the joint action of the bile and pancreatic secretion; a portion 
is saponified, which again helps in emulsification, while an 
additional part, in form but little changed, is probably dealt 
with by the absorbents. 
Proteid digestion is continued, and, besides peptones, ni- 
trogenous crystalline bodies are formed (leucin and tyrosin), 
but under what conditions or to what extent is not known; 
though the quantity is likely very variable, both with the spe- 
cies of animal and the circumstances, such as quantity and 
quality of food; and it is likely also dependent not a little on 
the rate of absorption. It seems altogether probable that in 
those that use an excess of nitrogenous food more of these 
bodies are formed, and thus give an additional work to the ex- 
creting organs, including the liver. But the absence of albu- 
min from healthy feces points to the complete digestion of 
proteids in the alimentary canal. Plainly the chief work of 
intestinal digestion is begun and carried on in the upper part 
of the tract, where the ducts of the main glands are to be 
found. 
The contents of the intestine swarm with bacteria, though 
