INFLUENCE OF NERVES ON THE SECRETION. 329 



such as stones. The mucous membrane becomes red, and the circulation 

 more active, so that the venous blood becomes brighter. [That the 

 vagi are concerned in this vascular dilatation, is proved by the fact, 

 that if both nerves be divided during digestion, the gastric mucous 

 membrane becomes pale (Rutherford).] The secretion is probably 

 caused reflexly, and the centre is perhaps in the wall of the 

 stomach itself, (Meissner's plexus in the sub-mucous coat). It is 

 asserted that the idea of food, especially during hunger, excites 

 secretion. As yet we do not know the effect produced upon the 

 secretion by stimulation or destruction of other nerves e.g., vagus, 

 sympathetic. [There is no nerve passing to the stomach, whose 

 stimulation causes a secretion of gastric juice, as the chorda tympani 

 does in the submaxillary gland. If the vagi be divided sufficiently 

 low down not to interfere Avith respiration, the introduction of food 

 still causes a secretion of gastric juice; even if the sympathetic branches 

 be divided at the same time, secretion still goes on (Heidenhain). This 

 experiment points to the existence of local secretory centres in the 

 stomach. But there is evidence to show that there is some connection, 

 perhaps indirect, between the central nervous system and the gastric 

 glands. Richet observed a case of complete occlusion of the oesophagus 

 in man, produced by sAvallowing a caustic alkali. A gastric fistula was 

 made, through which the person could be nourished. On placing sugar 

 or lemon-juice in the person's mouth, Richet observed secretion of 

 gastric juice. In this case, no saliA'a could be swalloAved to excite 

 secretion, so that it must have taken place through some nervous 

 channels. Even the sight or smell of food caused secretion. Emo- 

 tional states also are known to interfere Avith gastric digestion.] 



Heidenhain isolated a part of the mucous membrane of the fundus 

 so as to form a blind-sac of it, and he found that mechanical stimula- 

 tion caused merely local secretion. If, hoAvever, at the same time, 

 absorption of digested matter also occurred, secretion took place over 

 larger surfaces. 



The statement of Schiff, that active gastric juice is secreted only after absorption 

 of the so-called peptogenic substances (especially dextrin), is denied. 



Action Of Alcohol. Small doses of alcohol, introduced into the stomach, 

 increase the secretion of gastric juice; large doses arrest it. Artificial digestion 

 is not affected by 10 p.c. of alcohol, is retarded by 20 p. c., and is arrested 

 by stronger doses. Beer and wine hinder digestion, and in an undiluted form 

 they interfere with artificial digestion (Buchner). 



The gastric juice, which passes into the duodenum after gastric 

 digestion is completed, is neutralised by the alkali of the intestinal 

 mucous membrane and the pancreatic juice. Part of the pepsin is 

 re-absorbed as such, and is found in traces in the urine and muscle- 

 juice (Briicke). 



