364 CHEMISTRY 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 1 points out, the establishment of an acid reaction is not necessary 
for proteid digestion. In the pancreatic juice another proteolytic 
ferment, trypsin, 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 to 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."' Falk found that the bacillus 
of splenic fever (B. anfhracis) 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 ; hut, 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 (/r/s/rie 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 "Lebrbuch der physiol. Chemie," 1894. Aufl. 3, S. 141-14.'. 
2 Sieber, Journ. f. prakt. Ohem., Leipzig, 1880, Bd. xix. S. 433; Miquel, CentraXbl.f. 
(dig. Gsndktspflg., Bonn, 1884, Bd. ii. S. 403. See also Ziemke, Inaug. Diss., Halle, 1893 : 
Mester, Ztschr.f. Hin. Med., Berlin. 1894, Bd. xxiv. S. 441 ; Schmitz, Ztschr. f. physiol. 
.. Strassburg, 1S94, Bd. xix. S. 401. 
3 " Experiences sur la digestion," Traduit par Senebier. Geneva, 17S4. 
4 Virchow's Archiv, 1SS3, Bd. xciii. S. 177. 
5 Deutsche med. Wchiischr., Leipzig, 1884, No. 20, S. 309. 
,: Nicati and Lietsch, Rev. scient., Paris, 1884, p. 658 : ( 'ompt. rend. Acad. d. sc. Paris, 
1884, fcomexcix. S. 928; Koch, Deutsche med. Wchnschr., Leipzig 1884, No. 45, S. 7-J^. 
7 Ztschr.f. physiol. Chem., Strassburg, 1890. Bd. xiv. S. 75. 
