CHEMICAL MECHANISMS OP SECRETION 189 



to call forth a psychical flow, as by the use of a sound, or better, 

 through a gastric fistula without attracting the animal's attention, 

 produce their effect not by exciting peripheral nerve-endings in 

 the gastric mucosa, but by means of a chemical action upon the 

 secreting cells. This action may either be a direct one of the 

 substances themselves or more probably, according to Edkins's 

 observations, an indirect action in which these substances, similarly 

 to hydrochloric acid in the case of the duodenal mucosa, set free 

 an active substance chiefly from the pyloric portion of the gastric 

 mucosa. This substance, after being absorbed by the blood stream, 

 is carried to the secreting cells lying deeper in the mucosa, and also 

 to the secreting cells of the fundus, where it acts as a chemical 

 stimulant, and calls forth secretion. 



Edkins has studied- the effects of intravenous injection of 

 extracts made from different parts of the gastric mucosa. He 

 placed a certain amount of saline in the stomach, and then 

 determined the amount of acid formed in the stomach after the 

 injection of each extract to be tested into a vein by titrating 

 this saline for total acidity. 



The results obtained were as follows : 



"If an extract in 5 per cent, dextrin of the fundus mucous 

 membrane be injected into the jugular vein, there is no evidence 

 of secretion of gastric juice. If the extract be made with the 

 pyloric mucous membrane, there is evidence of a small quantity 

 of secretion. With dextrin by itself there is no secretion. 



" Extracts of fundus mucous membrane in dextrose or maltose 

 give no secretion ; extracts of pyloric mucous membrane give 

 marked secretion ; dextrose or maltose alone bring about no 

 secretion. 



" If extracts be made with commercial peptone, it is found 

 that no secretion occurs with the fundus mucous membrane, a 

 marked secretion with the pyloric mucous membrane ; the peptone 

 alone gives a slight secretion. 



" If the extracts be made by boiling the mucous membrane 

 in the different media, the effect is just the same, that is to say, 

 the active principle, which may be called ' gastrin,' is not destroyed 

 by boiling. 



" Finally, it may be pointed out that such absorption as occurs 

 in the stomach apparently takes place at the pyloric end. In 

 the pig's stomach, in which the cardiac region differs from the 



