246 INFLUENCE OF NERVES ON THE SECRETION. 



juice ; this takes place only after appropriate (mechanical, thermal, or chemical) 

 stimulation. In the normal condition, it takes place immediately on the introduc- 

 tion of food, but also of indigestible substances, such as pebbles. 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 perhaps lies 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 with 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 a woman, produced by swallowing 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 a secretion of gastric juice. 

 In this case no saliva could be swallowed to excite secretion, so that it must have 

 taken place through some nervous channels. Even the sight or smell of food caused 

 secretion. Emotional states also are known to interfere with gastric digestion.] 



Effect of Absorption. Heidenhain isolated a part of the mucous membrane of 

 the fundus so as to forma blind sac of it, and he found that mechanical stimulation 

 caused merely a scanty local secretion at the spots irritated. If, however, at the 

 same time, absorption of digested matter also occurred, secretion took place over 

 larger surfaces. [He distinguishes a primary and merely local secretion excited by 

 the mechanical stimulus of the ingesta, and a secondary depending on absorption, 

 and extending to the whole of the mucous membrane.] 



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

 called peptogenic substances (especially dextrin), is denied. 



The acid contents of the stomach called chyme, which pass into the duodenum 

 after gastric digestion is completed, are neutralised by the alkali of the intestinal 

 mucous membrane and the pancreatic juice, [at the same time, a precipitate is 

 formed and deposited on the walls of the duodenum, and it carries the pepsin down 

 with it]. Part of the pepsin is reabsorbed as such, and is found in traces in the 

 urine and muscle juice (Brilcke). If the gastric juice be completely discharged ex- 

 ternally through a gastric fistula, the alkalinity of the intestine is so strong that 

 the urine becomes alkaline (Maly). 



The acid gastric juice of the new-born child is already fairly active ; casein is most easily 

 digested by it, then fibrin and the other proteids {Zweifel). When the amount of acid is too 

 great in the stomach of sucklings, large firm indigestible masses of casein are apt to be formed, 

 especially after the use of cow's milk ( 230). 



[Action of Drugs on Gastric Secretion. Dilute alkalies, if given before food ; saliva ; some 

 substances called peptogens by Schiff, such as dextrin and peptones, alcohol and ether, all 

 excite secretion, the last being very powerful. When the secretion is excessively acid, antacids 

 are given, some diminishing the acidity in the stomach, as the carbonates and bicarbonates of 

 the alkalies, liquor potassae, and the carbonate of magnesia ; while the citrates and tartrates of 

 the alkalies, becoming converted into carbonates in their passage through the organism, diminish 

 the acidity of the urine.] Small doses of alcohol, introduced into the stomach, increase the 

 secretion of gastric juice ; large doses arrest it. Artificial digestion is affected by 10 per cent, 

 of alcohol, is retarded by 20 per cent., and is arrested by stronger doses. Beer and wine hinder 

 digestion, and in an undiluted form interfere with artificial digestion. 



