DIGESTION OF FOOD. 85% 
these are probably kept under control to some extent by the 
bile, the functions of which as an antiseptic we have already 
considered. 
The removal of fats by the villi will be shortly considered. 
The other products of digestion probably find their way into 
the general circulation by the portal blood, passing through 
the liver, which organ modifies some of them in ways to be 
examined later. 
The valvule conniventes greatly increase the surface of the 
intestine, and retard the movements of the partially digested 
mass, both of which are favorable. The peristaltic movements 
of the small gut serve the obvious purpose of moving on the 
digesting mass, thus making way for fresh additions of chyme 
from the stomach, and carrying on the more elaborated con- 
tents to points where they can receive fresh attention, both 
digestive and absorptive. 
Comparative—In man, the carnivora, and some other groups, 
it is likely that digestion in the large intestine is slight, the 
work being mostly completed—at all events, so far as the action 
of the secretions is concerned—before this division of the tract 
is reached, though doubtless absorption goes on there also. 
The muscular strength of this gut is important in the act of 
defecation. 
But the great size of the large intestine in ruminants—in 
the horse, etc.—together with the bulky character of the food 
of such animals, points to the existence of possibly extensive 
processes of which we are ignorant. It is generally believed 
that food remains but a short time in the stomach of the horse, 
and that the cecum is a sort of reservoir in which digestive 
“processes are in progress, and also for water. 
Fermentations go on in the intestine, and probably among 
ruminants they are numerous and essential, though our actual 
knowledge of the subject is very limited. 
The gases found in the human stomach are atmospheric air 
(swallowed) and carbon dioxide, derived from the blood. Those 
of the intestine are nitrogen, hydrogen, carbonic anhydride, 
sulphureted hydrogen, and marsh-gas, the quantity varying 
considerably with the diet. 
Pathological.—In subjects of a highly neurotic temperament 
and unstable nervous system it sometimes happens that im- 
mense quantities of gas are belched from an empty stomach or 
distend the intestines. 
It is known that the oxygen swallowed is absorbed into the 
