84 PHYSIOLOGY. 



teids are incapable of diffusion through animal membranes in the 

 act of absorption. 



Thus it can safely be stated that the prime and essential . func- 

 tion of the gastric secretion is to dissolve the proteids present and 

 convert them into peptones. 



Gastric juice exercises no amylolytic influences upon any starch 

 present; in fact, three-fourths of an hour after a meal, the action 

 going on due to the saliva swallowed with the food is stopped alto- 

 gether by reason of traces of free hydrochloric acid secreted by the 

 oxyntic cells. 



There is a fat-splitting ferment in the gastric juice of the fundus. 



Those mineral matters which can be dissolved in hydrochloric 

 acid of the strength of that found in the gastric juice are also dis- 

 solved in the stomach. The degree of solubility and efficiency at- 

 tained by the gastric secretion far surpasses that of simple, diluted 

 acid, probably because of the pepsin found in the former. 



Although the amylolytic action of the saliva on starch takes place 

 for a definite interval, the gelatinous envelopes of the fat-globules and 

 mineral substances are dissolved within the receptacle of the stomach, 

 yet the essential and characteristic feature of the work to be done 

 there is on the proteids: converting them into peptone through the 

 action of proteolysis. 



The proteids found in Nature are very complex and as yet not 

 thoroughly known. However much they, as individuals, may differ 

 in composition, reactions, etc., yet they all possess an inherent ten- 

 dency to undergo hydrolytic decomposition when conditions are favor- 

 able. Hydration and cleavage can be induced by simple heating in 

 water alone raised to the temperature of 100 C., for there results par- 

 tial solution of the proteids during the process. The proteolytic pro- 

 cess of the gastric secretion in its converting proteids into peptones 

 is also one of hydration and cleavage. The final products are not the 

 result of one simple step, not the formation of one simple body or 

 substance, as when the proteids are acted on by heated water alone. 

 The acid in gastric digestion induces a row of chemical changes and 

 products, each separate and distinct, and capable of being recognized 

 by certain reagents. 



By the action of pepsin-acid the proteid is first changed into (1) 

 synionin, or acid-albumin. By further action of the ferment, the 

 acid-albumins are changed into (2) proteases, with their divisions into 

 primary and secondary protease. The proteoses are the intermediate 

 products between acid-albumins and peptones. These are found un- 



