THE JUICES POURED OUT UPON THE FOOD. 67 



value was obtained long ago by HEIDENHAIN. In spite of the 

 majority of observations to the contrary, this high acidity 

 probably represents the true value under physiological con- 

 ditions. Because of this acidity, bacteria do not develop 

 well in gastric juice, and it may in consequence be kept for 

 a long time without undergoing decomposition. The acidity 

 of the normal gastric juice is due to hydrochloric acid. This 

 was first proved by PROUT and independently of him, but 

 later, by TIEDEMANN and GMELIN. The objections which 

 were raised against this idea by CLAUDE BERNARD and BER- 

 RESWIL have been set aside by the researches of ScHMiDT. 1 

 Traces of organic acids are at times found in the normal 

 gastric secretion. 



Human gastric juice does not differ in its physical or 

 chemical properties from canine juice. The concentration 

 of the acid and the pepsin is perhaps somewhat lower in 

 man. 



No complete analysis of gastric juice seems to be at hand. 

 Besides hydrochloric acid, gastric juice contains the fer- 

 ment acid-proteinase (pepsin), which has the power of acting 

 on proteins and splitting them into a number of simpler 

 bodies. Caseinase (rennin) is also found in the gastric 

 juice of the human being as well as that of other animals. 

 This ferment has the power of curdling milk. The hydro- 

 chloric acid present in the stomach is of itself able to 

 bring about this change, but the presence of the ferment 

 can be demonstrated by neutralizing the gastric juice 

 with an alkali, when it is found that the milk-curdling 

 power still persists. It is lost, however, when the neutral 

 gastric juice is heated to 70 C. for a short time. The 

 secretion of the stomach also contains a fat-splitting fer- 

 ment, lipase (steapsin), but its physiological importance 

 is probably small, as the ferment acts little or not at all 



1 For an interesting account of the subject, see MOORE: Text-book of 

 Physiology, edited by SCHAEFER, Edinburgh, 1898, I, p. 351. 



