336 ANIMAL PHYSIOLOGY. 
the least perfect, viewed as an investing coat. The pyloric end 
of the stomach is best supplied with muscles; where also there 
is a thick muscular ring or sphincter, as compared with which 
the cardiac sphincter is weak and ill-developed. 
The movements of the stomach begin shortly after a meal 
has been taken, and, as shown by observations on St. Martin, 
continue for hours, not constantly, but periodically. The effect 
of the conjoint action of the different sets of muscular fibers is 
to move the food from the cardiac toward the pyloric end of 
the stomach, along the greater curvature and back by the lesser 
curvature, while there is also, probably, a series of in-and-out 
currents to and from the center of the food-mass. The quantity 
of food is constantly being lessened by the removal of digested 
portions, either by the blood-vessels of the organ or by its 
passing through the pyloric sphincter. The empty stomach is 
quiescent and contracted, its mucous membrane being thrown 
into folds. 
The movements of the stomach may be regarded as reflex, 
the presence of food being an exciting cause, though probably 
not the only one; and so largely automatic is the central mech- 
anism concerned, that but a feeble stimulus suffices to arouse 
them, especially at the accustomed time. 
Of the paths of the impulses, either afferent or efferent, 
little is known. Certain effects follow section or stimulation of 
the vagi or splanchnics, but these can not be predicted with 
certainty, or the exact relation of events indicated. : 
It is said that the movements of the stomach cease, even 
when it is full, during sleep, from which it is argued that gas- 
tric movements do normally depend on the influence of the 
nervous system. However, the subject is too obscure at pres- 
ent for further discussion. 
Comparative.—Recent investigations on the stomach of the 
pig indicate that in this animal the contents of the two ends of 
the stomach may long remain but little mingled; and such is 
certainly the case in-this organ among ruminants. 
Pathological.— Distention of the stomach, either from excess 
of food or gas arising from fermentative changes, or by secre- 
tion from the blood, may cause, by upward pressure on the 
diaphragm, etc., uneasiness from hampered respiration, and ir- 
regularity of the heart, possibly, also, in part traceable to the 
physical interference with its movements. After great and 
prolonged distention there may be weakened digestion for a 
considerable interval. It seems not improbable that this is to 
