DIGESTION 



373 



rpsa 

 Musculans 



gastric glands are favourably situated for direct stimulation, while 

 the large salivary glands are not ; and that the great function of 

 saliva being to aid deglutition, an almost momentary, and at 

 the same time a perilous act, it is necessary to provide by a 

 nervous mechanism for an immediate rush of secretion at any 

 instant, while it is not important whether the gastric juice is 

 poured out a little sooner or a little later, and therefore it is left 

 to be called forth by the more tardy and haphazard method of 

 local action. Nevertheless, on looking a little closer, we find 

 that this does not exhaust the subject, and that the gastric 

 secretion can 



be influenced 2 



by events 

 taking place 

 in distant 

 parts of the 

 body, just as 

 the salivary 

 secretion 

 can. In a boy 

 whose oeso- 

 phagus was 

 c o m p 1 e t ely 

 closed by a 

 cicatrix, the 

 result of 

 swallowing a 

 strong alkali, 

 and who had 

 to be fed by 

 a gastric fis- 

 tula, it was 

 found that 

 the presence 

 of food in the 

 mouth, and 

 even the sight or smell of food, caused secretion of gastric 



juice (Richet). 



Here there must have been some nervous mechanism at work. 

 The secretion cannot have been excited by the direct action of 

 absorbed food-products circulating in the blood an explanation 

 which might be given, though an insufficient one, of the secretion 

 seen in an isolated portion of the cardiac end of the stomach 

 during the digestion of food in the rest. The efferent nervous 

 channels through which these effects are produced have been 

 defined by Pawlow's experiments on dogs. He first made 



FIG. 145. PAWLOW'S STOMACH POUCH. 

 S, the completed pouch ; V, cavity of stomach. 



