474 DIGESTION 



process in the stomach might account for the continued secretion of 

 gastric juice. To test such a 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 physiological saline. After this had been in the stomach 

 for an hour, he found that no water was absorbed, and that 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 min- 

 utes, the saline contained distinct quantities of hydrochloric acid and pep- 

 sin. 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 

 appetite juice. By such a mechanism gastric juice would continue to be 

 secreted so long as any half-digested food remains in the stomach. 



The action of gastrin is the first instance of a hormone control of the 

 digestive glands. In the earlier stages of digestion, the secretion of saliva 

 and appetite juice is mediated through the nervous system, because these 

 juices must be produced promptly. In the later stages of gastric diges- 

 tion, such promptitude in response on the part of the gland is no longer 

 necessary, so that the slower, more continuous process of hormone con- 

 trol is sufficient. 



Quantity of Gastric Juice Secreted 



According to Carlson, the total amount of gastric juice secreted in 

 man on an average meal composed of meat, bread, vegetables, coffee or 

 milk, and dessert, amounts to about 700 c.c., being divided into 200 c.c. 

 in the first hour, 150 in the second, and 350 c.c. during the third, fourth 

 and fifth hours. These figures were estimated partly on the basis of 

 observations made on the man with the gastric fistula, and partly from 

 the data supplied by Pavlov's observations on dogs. Carlson believes 

 that Pavlov overestimated the relative/ importance of the appetite juice 

 in gastric digestion. He found, for example, that after division of both 

 vagus nerves in dogs normal gastric digestion might be regained a few 



