TRANSFERENCE OF FOOD MATERIALS 123 



There is a second mechanism, of a more chemical nature, 

 which aids in causing the secretion of gastric juice. Edkins 

 has shown that by extracting the pyloric end of the stomach 

 with solutions of meat extract, dextrin, glucose, etc., a solution 

 is obtained which on injection into the blood stream causes a 

 secretion of acid and pepsin.* 



As the active substance is extracted by the products of 

 digestion of starch and of protein it is not formed until 

 digestion has commenced. The time at which it is formed is 

 after the external stimuli of taste, smell, etc., have disappeared, 

 hence it is well adapted to promote the later stages of gastric 

 digestion. 



Chemical substances which are formed in one part and 

 stimulate another part to activity -have been termed Hor- 

 mones, f Other examples of hormones will be discussed later 

 on. Edkins suggested the name Gastrin for the hormone found 

 by him in the stomach. 



TABLE XXIV 



Composition of Gastric Juice. J 



Parts per 1,000. 



Protein (Ferment, etc.) I 5'742 



Hydrochloric acid 2-022 



Sodium chloride 1*381 



Potassium chloride _ 0-818 



Calcium chloride 0-053 



Ammonium chloride 4 "5 17 



Calcium phosphate 2-971 



Magnesium phosphate '357 



Ferric phosphate 0-257 



of which the first two are the only important items. 



The discussion on the secretion of saliva applies to the 

 secretion of gastric juice. The histological changes, dis- 

 appearance of granules, etc., are the same. The secretion of 

 acid is confined to one portion (fundus) in the glands of which 

 are found certain large oval cells which stain readily with 

 acid dyes (e.g. eosin). They are called oxyntic cells and are 

 believed to be associated with the secretion of acid. The 

 other portions of the stomach secrete the enzymes but no acid. 



The food is retained in the stomach for some time, after 

 which the pylorus opens and allows some of the contents to 

 escape into the first portion of the small intestine (duodenum). 

 The mechanism that regulates the escape of the stomach 



* J. S. Edkins, Journ. Physiol., 1906, vol. 34, p. 133. 

 f W. M. Bayliss and E. H. Starling, Journ. Physiol., 1902, vol. 

 28, p. 325. 



I F. Bidder and C. Schmidt, Die Verdauungsdfte, 1852, p. 61. 



