80 NUTRITIONAL PHYSIOLOGY 



and in an earthen container, we can appreciate their 

 feeling. For here is what we call a strong mineral acid 

 proceeding from delicate living cells and from fluids of 

 neutral reaction. The formation of hydrochloric acid by 

 the cells of the gastric glands has become much more 

 intelligible in the light of modern chemical teachings. 

 The current theories cannot be presented here. It is 

 evident that when the elements of an acid are withdrawn 

 from a neutral fluid it must, theoretically at least, be 

 rendered alkaline. We have a capital illustration of the 

 refinement of the mechanism by which the body preserves 

 uniform internal conditions in the fact that when gastric 

 juice is being secreted, the urine, usually acid to common 

 indicators, becomes alkaline. Thus the normal chemical 

 equilibrium of the blood is maintained sacred from disturb- 

 ance. The juice secreted into the antrum is said not to be 

 acid. 



Mention has been made of some ways in which the acid 

 of the stomach modifies local conditions. We have seen 

 that it gradually checks salivary digestion. It is the most 

 important controlling factor for the two sphincters. 

 Other features of its action must now be presented. 

 Among these is its distinct antiseptic infleunce. Spallan- 

 zani noticed that pieces of meat undergoing digestion in 

 gastric juice passed into solution without putrefying. 

 Similar pieces kept for an equal time in water had radically 

 spoiled. This was a significant observation "at the time, 

 because digestion and putrefaction had been regarded by 

 many as identical. We know now that putrefactive de- 

 composition of protein is due to the influence of swarming 

 micro-organisms, and that hydrochloric acid in the con- 

 centration usual in the gastric juice restrains the develop- 

 ment of such forms. 



The average strength of the acid in man is given as 

 0.2 to 0.3 per cent. Such a concentration by no means 

 suffices to sterilize the stomach-contents, but in all prob- 

 ability it destroys many kinds of bacteria, including some 

 which might become the cause of disease. Others it un- 



