364 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



Function of the hydrochloric acid. One obvious purpose of the 

 hydrochloric acid of the gastric juice is to confer activity on the pepsin 

 accompanying it, which is only active in an acid medium. But, as 

 Bunge l points out, the establishment of an acid reaction is not necessary 

 for proteid digestion. In the pancreatic juice another proteolytic 

 ferment, trypsiii, is found, which acts most powerfully on proteids in an 

 alkaline medium. A much more important function of the hydrochloric 

 acid lies, according to Bunge, in its powerful action as a disinfectant 

 and germicide, in destroying bacteria introduced with the food. In this 

 manner the formation of decomposition products, and the disturbance 

 thereby produced in the normal course of digestion, is prevented, and 

 also in many cases the animal is preserved from the attacks of patho- 

 genic bacteria by the destruction of these or their spores. 



Modern research has, in fact, led tf> the remarkable result, that the 

 average amount of hydrochloric acid found in the gastric juice just about 

 coincides with that which is found experimentally to be required to stop 

 the growth of most fermentative organisms and many pathogenic 

 bacteria. 2 



Spallanzani 3 first called attention to the powerful preservative action 

 of gastric juice, and not only showed that gastric juice prevented 

 putrefaction, but that it stopped putrefaction which had already com- 

 menced. This he showed by feeding dogs on pieces of flesh which had 

 commenced to putrefy. After a short interval of gastric digestion the 

 flesh lost all putrefactive odour. 



The action of the gastric juice on the bacilli of tubercle and splenic fever 

 has been investigated by Falk, 4 and by Frank. 5 Falk found that the bacillus 

 of splenic fever (B. anthracis) is easily destroyed by gastric juice, but that 

 its spores escape destruction, and that the tubercle bacillus is unaffected by 

 gastric juice. Frank completely confirms these results, and both observers 

 are agreed that the gastric juice is incapable of making any very effectual 

 resistance to infection of the organism by these pathogenic bacteria. The 

 comma bacillus of cholera, however, is readily destroyed by gastric juice or 

 dilute hydrochloric acid. 6 Cholera cannot be communicated by the mouth in 

 healthy animals ; but, after washing out the stomach with alkaline solutions, 

 symptoms resembling those of cholera follow introduction of a pure culture of 

 the cholera bacillus, as is also the case when this is introduced into the 

 intestine. 



The acetic and lactic fermentations are stopped by mere traces of free 

 hydrochloric acid, while acid combined with proteid is ineffectual. According 

 to Cohn, this action is due to the free acid decomposing the alkaline phosphates, 

 which are necessary for the growth of the bacteria. 7 



Qualitative tests for free hydrochloric acid in gastric juice. The 

 many colour tests for detecting the presence of free hydrochloric acid 

 in gastric juice, in contradistinction to organic acids, are all more or 



1 "Lehrbuch der physiol. Chemie," 1894, Aufl. 3, S. 141-145. 



a Sieber, Journ. f. prakt. Chem., Leipzig, 1880, Bd. xix. S. 433 ; Miquel, CenlralU. f. 

 (dig. Gsndlitspjlg., Bonn, 1884, Bd. ii. S. 403. See also Ziemke, Inaug. Diss., Halle, 1893 ; 

 Hester, Ztschr.f. klin. Med., Berlin, 1894, Bd. xxiv. S. 441 ; Schmitz, Ztscltr. f. physiol. 

 Chem., Strassburg, 1894, Bd. xix. S. 401. 



3 " Experiences sur la digestion," Traduit par Senebier, Geneva, 1784. 



4 Virchoufs Archiv, 1883, Bd. xciii. S. 177. 



5 Deutsche mcd. Wchnschr., Leipzig, 1884, No. 20, S. 309. 



6 Nicati and Lietsch, Rev. sclent., Paris, 1884, p. 658 ; Compt. rend. Acad. d. sc., Paris, 

 1884, tomexcix. S. 928; Koch, Deutsche med. Wchnschr., Leipzig, 1884, No. 45, S. 725. 



7 Ztschr. f. physiol. Chem., Strassburg, 1890, Bd. xiv. S. 75. 



