212 PHYSIOLOGY OF ALIMENTATION. 



which occurs at first is found even when the food never 

 really enters the stomach, as in sham feeding. Since this 

 secretion is associated with the passionate desire for food, 

 or with the mental impressions produced by the sight, 

 smell, taste, etc., of the food, it is termed the " psychic" 

 element in gastric secretion. The channel over which the 

 mental stimulation reaches the stomach and excites the lat- 

 ter to secretory activity is represented by the vagus nerves. 

 When these are cut the initial rise in gastric secretion does not 

 occur. The second great rise in the curve of gastric secretion 

 following an ordinary meal nevertheless occurs. In what 

 way is this second rise brought about? 



The observations of EDKINS l give us an answer to this 

 question. Familiar with the experiments of BAYLISS and 

 STARLING on pancreatic secretin, 2 EDKINS cast about to find 

 a gastric secretin. His experiments show that under the in- 

 fluence of certain digestion products t the mucosa of the pyloric 

 end of the stomach produces, during the period of digestion, a sub- 

 stance gastric secretin which is absorbed into the blood and 

 which excites the gastric glands to increased secretion. To 

 prove this EDKINS prepared extracts of the mucous membrane 

 of the pyloric end of < the stomach by rubbing this up in a 

 mortar with 5 percent dextrin solutions, or solutions of 

 various sugars and peptones. If repeated small doses of 

 this extract are injected into the circulation of a dog which 

 has had its stomach filled with a physiological salt solution, 

 it is found at the end of an hour that the salt solution con- 

 tains both hydrochloric acid and acid proteinase. A secretion 

 of gastric juice is therefore excited by these extracts. It 

 can be shown in control experiments in which dextrin, pep- 

 tone^ ^etc., are injected in pure solution into the circulation 

 that no hydrochloric acid or acid-proteinase can be found 

 in the physiological salt solution recovered from the stomach. 



1 EDKINS: Journal of Physiology, 1906, XXXIV, p. 133; STARLING: 

 Lancet, 1905, CLXIX, p. 501. 



2 See p. 227. 



