EXPERIMENTS ON DIGESTION. 
365 
The vascular layer, covered by a dense ramification of bloodves- 
sels, thickens; and the muscular coat, composed of longitudinal, 
circular, and oblique fibres, is distended, in every sense of the term. 
In proportion as the stomach fills, it dilates, and its axis under- 
goes a kind of torsion. Its horizontal position in the dog and the 
horse not permitting it to dilate superiorly, on account of the re- 
sistance opposed to it by the vertebral column, it takes a direction 
downwards towards the abdominal muscles, and in such a manner 
that its larger curvature is directed downwards, while its smaller 
one takes an upward direction. 
The food, in general only grossly divided, which has been re- 
ceived into the stomach, cannot in this state escape through the 
pyloric orifice. The valve of that orifice, and the contraction of the 
strong muscular fasciae which surround it like a circle, will not per- 
mit it to pass into the duodenum. The horizontal position of the 
body of the dog and the horse which causes the stomach to be found 
nearly on a level with the termination of the oesophagus, would 
seem to suggest the idea that the return of the aliment through the 
oesophagus would be easy ; but this cannot ordinarily take place, on 
account of the contraction of the muscular membrane of the oesopha- 
gus, which is much thicker and stronger than that of the stomach. 
Besides, the oesophagean canal is contracted upon itself whenever 
it is empty, and it is only during the act of deglutition that it is 
forced into a state of distention. As soon as, by its contraction, it 
has forced the pellet of food into the stomach, it returns to its ordi- 
nary state of contraction and occlusion, so as to render the return 
of the food, by any natural process, impossible. 
The contraction and the occlusion of the cardiac and pyloric ori- 
fices, by the contraction of the muscular rings which surround them, 
are so considerable, that even, when we take out the stomach of an 
animal immediately after death, these orifices will scarcely permit 
a particle of food to pass, as we have many times seen. 
Sir Everard Home pretends to have observed that the stomach 
of dogs during the process of digestion experiences a contraction 
about the middle of it, so as to form it into two cavities, — a cardiac 
and a pyloric. He adds, that the first contains the aliment grossly 
comminuted by the act of mastication, and the portions of food which 
have been last swallowed, while the latter is destined for the more 
perfectly dissolved and half digested contents. We have never seen 
this division of the stomach in any of the numerous experiments 
which we have made on the dog, the cat, or the horse, therefore 
we do not hesitate to consider it as a groundless hypothesis, founded 
on careless or inexact observation. 
3 c 
VOL. XII. 
