DIGESTION OF POOD. 337 



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- 

 anisms concerned that but a feeble stimulus sufHces 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 present 

 for further discussion; 



Comparative. — Eecent 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 

 irregularity 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 

 be explained, not alone by the impaired elasticity (vitality) of 

 the muscular tissue, but also by defective secreting power. It 

 is not necessary to impress the lesson such facts convey. 



The Intestinal Movements.— The circular fibers play a much 

 more important part than the longitudinal, being, in fact, much 

 more developed. It is also to be remembered that nerves in 

 22 



