DIGESTION 375 



the large, is markedly delayed and scanty when it does appear. 

 Bread and coagulated egg-white did not yield a single drop 

 during the first hour or more. Raw flesh excited a secretion, 

 but after an interval of fifteen to forty-five minutes, instead of 

 five or six to ten, as in sham feeding. It was very scanty during 

 the first hour (only one-third the normal amount), and possessed 

 a very low digestive power. The importance of the psychical 

 element is shown by the fact that in one dog, which, after a 

 weighed amount of meat had been introduced into its stomach 

 (without its knowledge) received a sham meal of meat, the 

 amount of protein digested after one and a half hours was five 

 times greater than in another animal treated exactly in the same 

 way, except that the sham meal was omitted. But even after 

 division of the vagi, gastric secretion is still caused by the intro- 

 duction of various substances into the stomach, especially water 

 and meat extract. The active substances in the meat extract 

 are, for the most part, insoluble in alcohol. Kreatin is inactive. 

 It is in virtue of these substances that raw meat placed directly in 

 the stomach causes some secretion after a time. Milk and gelatin 

 solution are also direct excitants of gastric secretion apart from 

 the water in them. Starch, fat, and egg-white are totally 

 inert. After section of both vagi in dogs, no marked quali- 

 tative or quantitative changes have been observed in the gastric 

 juice. The secretion caused by the presence of food in the 

 stomach is still obtained when, in addition to the vagi, all other 

 nerves which can possibly connect the central nervous system 

 with the organ have been severed and the sympathetic abdo- 

 minal plexuses have been destroyed (Popielski). We must 

 therefore suppose that the gastric glands, while normally under 

 the control of a nervous mechanism in the upper portion of the 

 cerebro-spinal axis whose efferent fibres run in the vagi, are also 

 capable of being locally stimulated through the peripheral 

 ganglia in the stomach walls or the chemical action of the products 

 of digestion absorbed into the blood. Edkins showed that the 

 injection of food substances or the products of their digestion 

 (broth, dextrin, peptone) or of acid into the blood caused no 

 secretion of gastric juice, while the injection of an extract of 

 the pyloric mucous membrane, made by boiling it with water, 

 acid, or peptone, excited a certain amount of secretion. He 

 therefore concluded that the secondary secretion of gastric 

 juice is determined, not by local stimulation of a reflex mechanism 

 in the gastric wall, but by the production in the mucous membrane 

 of the pyloric end of a chemical substance, the gastric secretin or 

 gastric hormone,* which is absorbed by the blood, and acts as 



* ' Hormone ' (from op^ow, I arouse or excite) is the name given to a 

 substance which, carried by the blood from the place where it is formed 



