196 STOMACH DIGESTION. 



mation is still undecided, and various theories have been pro- 

 pounded to explain it. Among these, Maly's is, perhaps, the one 

 most generally accepted. This theory is that there occurs a 

 reaction between the phosphates and chlorids of the blood which 

 results in the formation of hydrochloric acid. This reaction is 

 expressed by the following equation : 



NaH 2 P0 4 + NaCl Na 2 HPO 4 + HC1 



Sodium dihydrogen Sodium Disodium hydrogen Hydrochloric 



phosphate. chlorid. phosphate. acid. 



Or the hydrochloric acid may be produced by the reaction be- 

 tween calcium chlorid and disodium hydrogen phosphate, as 

 follows : 



3CaCl 2 + 2Na 2 HPO 4 Ca3 (PO 4 ) 2 + 4NaCl -f 2HC1 



Calcium Disodium hydrogen ' Calcium Sodium Hydrochloric 



chlorid. phosphate. phosphate. chiorid. acid. 



This theory regards the formation of the hydrochloric acid as 

 taking place in the blood ; and being highly diffusible, it diffuses 

 through the gastric glands into the stomach. In this explanation 

 the cells have no part in the formation of the acid. Gamgee re- 

 gards the cells of the glands, those known as parietal or oxyntic, 

 as the acid producers, and supposes that they have a peculiar 

 power of selecting the alkaline phosphates and the chlorids from 

 the other constituents of the blood, and that the reaction already 

 referred to takes place in them, hydrochloric acid resulting. But, 

 as we have already said, this is pure theory, and has never been 

 demonstrated. About all that can be said is that the hydrochloric 

 acid is probably produced by the parietal cells from the chlorids 

 of the blood, and that is their special function, as is that of the 

 chief cells to produce pepsinogen or the cells of the salivary 

 glands to produce ptyalin. 



Besides the action of hydrochloric acid in connection with 

 digestion, it has still another which is under some circumstances 

 one of great importance that is, its action on pathogenic bacteria ; 

 we shall discuss the subject of Bacterial Digestion later (p. 253), 

 but here we desire to call attention to the protective influence 

 which the hydrochloric acid of the gastric juice exerts against 

 certain well-known diseases. 



The preservative power of gastric juice on meat, due to the 

 action of the hydrochloric acid on putrefactive bacteria, has long 

 been known. The cholera spirillum, the germ which produces 

 Asiatic cholera, will not survive in fluid of the acidity of the 

 gastric juice of the guinea-pig and the rabbit. Nor has cholera 

 been produced when, after first neutralizing the gastric juice 

 by administering soda, cholera cultures have been ingested. But 

 if opium is given with the soda, and intestinal peristalsis slowed 



