336 HUMAN PHYSIOLOGY 



This may be separated from pepsin in various ways, and 

 unlike pepsin it acts in a neutral medium. 



The change set up by it seems to be due to a splitting 

 of the soluble lime salt of casein which exists in milk 

 into calcic paracasein, which is insoluble and is thrown 

 down, while a small quantity of whey albumin remains 

 in solution. The nuclein part of the paracasein remains 

 undigested. 



On Fats the gastric juice has no action, but, when these 

 are contained in the protoplasm of cells, it sets them free by 

 digesting the proteid covering. 



On Carbohydrates the free mineral acid of the gastric 

 juice has a slight action at the body temperature, splitting 

 the polysaccharids and disaccharids into monosaccharids. 



(c) Digestion of the Stomach Wall. When the wall of 

 the stomach dies either in whole, as after the death of the 

 animal, or in part, as when an artery is occluded or ligatured, 

 the dead part is digested by the gastric juice and the wall of 

 the stomach may be perforated. 



(d) Antiseptic Action of the Gastric Juice. In virtue of 

 the presence of free HC1 the gastric juice has a marked action 

 in inhibiting the growth of or in killing bacteria. The bacillus 

 of cholera is peculiarly susceptible, and a healthy condition of 

 the stomach is thus a great safeguard against the disease. 

 Other organisms, while they do not multiply in the stomach, 

 pass on alive to the intestine where they may again become 

 active. When HC1 is not formed in sufficient quantities to 

 exist free in the stomach, the activity of these bacteria 

 may lead to various decompositions and to many of the 

 symptoms of dyspepsia. 



(e) Source of the Constituents of the Gastric Juice. 



The hydrochloric acid is formed at the cardiac end of the 

 stomach. This may be shown by isolating a part of the 

 stomach so that it opens on the surface. Since the parietal 

 or oxyntic cells are confined to this portion of the stomach, it 

 may be concluded that they are the producers of the acid. 

 They manufacture it from the NaCl of the blood plasma. 



