CHAPTER VIII. 



THE GASTRIC JUICE AND CHANGES IN THE STOMACH. 



The gastric juice free from saliva and particles of food is 

 a thin liquid with specific gravity ranging from i.ooi to i.oio. 

 It contains besides certain enzymes some small amounts of 

 protein matters, a little sodium chloride and traces of other 

 salts and free hydrochloric acid. Lactic acid is also frequently 

 present in traces. The older analyses of human gastric juice 

 which have been frequently quoted are misleading, as they 

 were made with material containing saliva and food products. 

 By aid of a fistula it has been possible to obtain a fairly nor- 

 mal secretion from certain animals, especially from the dog, 

 and much of our knowledge of the conditions of secretion and 

 variations in composition has been secured in this way. The 

 physiologically important substances in the gastric juice are 

 free hydrochloric acid, pepsin and rennin. 



The secretion is furnished by two kinds of glands known as 

 the pyloric glands and the fundus glands. Both groups of 

 cells yield the two enzymes, but the pyloric cells do not seem 

 to furnish an acid secretion. It is probable that certain of 

 the fundus cells only are concerned with the acid secretion. 

 The gastric secretion is promoted by two kinds of stimuli. 

 Certain chemical substances when taken into the stomach have 

 the power of exciting a flow of the juice from the mucous 

 membrane, and are themselves not subject to gastric digestion. 

 Small amounts of alcohol, ether, spices and meat extracts act 

 in this way. But more important than this is the so-called 

 " psychic " stimulus, depending on the desire for food and the 

 satisfaction derived from partaking of it. The amount of the 

 secretion varies with the nature and kind of food. 



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