330 ANIMAL PHYSIOLOGY. 
The first view (the alkalinity of the blood) would not suffice 
to explain why the pancreas, the secretion of which acts best 
in an alkaline medium, should not be digested. 
It seems to us there is a good deal of misconception about 
the facts of the case. Observation on St. Martin shows that 
the secretion of gastric juice runs parallel with the need of it, 
as dependent on the introduction of food, its quantity, quality, 
etc. Now, there can be little doubt that, if the stomach were 
abundantly bathed when empty with a large quantity of its 
own acid secretion, it would suffer to some extent at least. 
But this is never the case; the juice is carried off and mixed 
with the food. This food is in constant motion and doubtless 
the inner portions of the cells, which may be regarded as the 
discharging region, while the outer (next the blood capillaries, 
the chief manufacturing region of the digestive ferment) are 
frequently renewed. 
Such considerations, though they seem to have been some- 
what left out of the case, do not go to the bottom of the 
matter. Amoeba and kindred organisms do not digest them- 
selves. Some believe that the little pulsatile vacuoles of the 
Infusorians are a sort of temporary digestive cavities. 
But, to one who sees in the light of evolution, it must be 
clear that a structure could not have been evolved that would 
be self-destructive. 
The difficulty here is that which lies at the very basis of all 
life. We might ask, Why do living things live, since they are 
constantly threatened with destruction from within as from 
without ? Why do not the liver, kidney, and other glands that 
secrete noxious substances, poison themselves? We can not 
in detail explain these things; but we wish to make it clear 
that the difficulty as regards the stomach is not peculiar to 
that gland, and that even from the ordinary point of view it 
has been exaggerated. 
Comparative-—More careful examination of the stomachs of 
some mammals has revealed the fact that in several animals, 
in which the stomach appears to be simple, it is in reality 
compound, There are different grades, however, which may 
be regarded as transition forms between the true simple 
stomach and that highly compound form of the organ met 
with in the ruminants. 
It has been shown recently that the stomach of the hog has 
an cesophageal dilatation; and that the entire organ may be 
divided into several zones with different kinds of glandular 
