GASTRIC DIGESTION. Up 



in reaction and has a specific gravity varying between i.ooi and 

 i.oio. It contains only 2-3 per cent of solid matter which is made 

 up principally of hydrochloric acid, sodium chloride, potassium 

 chloride, earthy phosphates, mucin and the enzymes pepsin, gastric 

 rennin and gastric lipase; the hydrochloric acid and the enzymes 

 are of the greatest importance. The acidity of the gastric juice is 

 due to free hydrochloric acid which is secreted by the parietal cells 

 of the fundus as well as by the chief cells of both the fundus and 

 pyloric glands, and, in man, is generally present to the extent of 

 0.2-0.3 per cent. When the amount of hydrochloric acid varies to 

 any considerable degree from these values a condition of hypoacidity 

 or hyperacidity is established. Hydrochloric acid has the power of 

 combining with protein substances taken in the food, thus forming 

 so-called combined hydrochloric acid. This combined acid is a less 

 potent germicide than free hydrochloric acid and has less power to 

 destroy the amylolytic enzyme salivary amylase (ptyalin) of the 

 saliva. This last fact explains to a degree the possibility of the 

 continuance of salivary digestion in the stomach. The hydrochloric 

 acid of the gastric juice forms a medium in which the pepsin can 

 most satisfactorily digest the protein food, and at the same time 

 it acts as an antiseptic or germicide which prevents putrefactive 

 processes in the stomach. It also possesses the power of inverting 

 cane sugar, this property being due to the hydrogen ion. When 

 the hydrochloric acid of the gastric juice is diminished in quan- 

 tity (hypoacidity) or absent, as it may be in many cases of func- 

 tional or organic disease, there is no check to the growth of micro- 

 organisms in the stomach. There are however certain of the 

 more resistant spores which even the normal acidity of the gastric 

 juice will not destroy. A condition of hypoacidity may also give 

 rise to fermentation with the formation of comparatively large 

 amounts of such substances as lactic acid and butyric acid. 



The question of the origin of the hydrochloric acid of the gastric 

 juice is a problem to w r hose solution many investigators have given 

 much attention. Many theories have been proposed, among them 

 being Bunge's mass action theory, Koppe's electrolytic dissociation 

 theory, and the more recent theory based upon the interaction of 

 sodium chloride and lactic acid. We cannot go into a discussion 

 of these various theories. Each of them has met with objection 

 and we have, as yet, no generally accepted theory as to the origin 

 of the hydrochloric acid of the gastric juice. That this hydrochloric 

 acid originates from the chlorides of the blood is apparently a well 



