PHYSIOLOGY OF THE DIGESTIVE GLANDS 439 



the difference in weights the extent to which they had become digested. 

 It was found that when the appetite juice was excited by sham feeding 

 at the same time that food was placed directly in the stomach, its diges- 

 tion was much more rapid than in cases in which it was placed in the 

 stomach without the animal's knowing, as when he was asleep. 



Other foods having a direct stimulating effect on the gastric secre- 

 tion are meat extracts and, to a certain extent, milk. This effect of meat 

 extract is interesting in connection with the practice of taking soup as 

 a first or early stage in dining. It not only excites the appetite juice, 

 but also serves as a direct stimulus to the gastric secretion. 



As to the nature of the -mechanism by which this direct secretion takes- 

 place, it was shown by Popielski 10a that the secretion still occurs after all 

 the nerves proceeding to the stomach are cut. Evidently, therefore, it 

 is independent of the extrinsic nerve supply of the viscus. As a result 

 of his experiments Popielski concluded that the secretion must depend 

 on a local reflex mediated through the nerve structures present in the 

 walls of the stomach itself. Another explanation of the result has, 

 however, in recent years been given more credence by the experiments of 

 Bayliss and Starling on the influence of hormones on the secretion of 

 pancreatic juice (cf. page 425). Edkins 10 suggested that a similar 

 process in the stomach might account for the continued secretion of 

 gastric juice. To test the possibility this investigator, after ligating the 

 cardiac sphincter in anesthetized animals, inserted a tube into the 

 pyloric end of the stomach, through which he placed in the stomach 

 about 50 c.c. of physiologic saline. After this had, been in the stomach 

 for an hour, he found that no water was absorbed, and that if the fluid 

 was removed after this time, it contained neither hydrochloric acid nor 

 pepsin. On the other hand, if during the time the saline was in the 

 stomach a decoction of the mucous membrane of the pyloric end, made 

 either with peptone solution or with a solution of dextrine, was injected 

 intravenously in small quantities every few minutes, it was found that 

 the saline contained distinct quantities of hydrochloric acid and pepsin. 

 Furthermore, it was found that, if the peptone solution or the dextrine 

 solution alone was injected intravenously, there was no such evidence 

 of gastric secretion. The conclusion which Edkins drew from his experi- 

 ments is to the effect that the half-digested products of the earlier stages 

 of gastric digestion act on the mucous membrane of the stomach so as to 

 produce a hormone, which is then carried by the blood to the cells of 

 the gastric glands, upon which, like secretin, it directly develops an 

 exciting effect. This hormone has been called gastrin. These observa- 

 tions of Edkins have been confirmed, and they explain very simply how 

 gastric secretion is maintained after the cessation of the secretion of the 



