HYDROGEN ION CONCENTRATION AND PROTEOLYSIS. 141 



REVIEW OF PREVIOUS INVESTIGATIONS. 



The influence of acidity and alkalinity upon biologic processes has been 

 investigated by many who are engaged in the study of general physiology, 

 as has been intimated in the introduction. In physiologic investigation 

 of bacterial life, Kisch's method ^ was generally employed previous to the 

 introduction of the physico-chemical method. Sieber- investigated the 

 antiseptic value (minimum dose) of different acids upon various bacteria. 

 Schluter^ found that M. prodigiosus grows very well in lactic acid 0.1 per 

 cent., but not higher. Carbett^ showed that Bactermm diphtherioe is able 

 to grow in higher acidity than M. prodigiosus. Proskauer and Beck* 

 pointed out that Bacterium tuberculosis lives in higher aciditj'' than the 

 other organisms mentioned above. 



Similar experiments were carried out to determine the influence of 

 alkalinity. Kitasato^ demonstrated that B. typhosus is killed by 0.1 to 

 0.14 per cent. KOH and Vibrio cholera by 0.18 per cent. KOH solution. 

 Liborius^ experimented with potassium carbonate and discovered that 

 most bacteria withstood 0.5 per cent., B. typhosus 0.8 per cent, and Vibrio 

 cholerce asiaticce 1.0 per cent. K2CO3 solution. . Deeleman^ ascertained 

 that the optimum alkalinity for most bacteria is approximately between 

 0.34 and 1.7 per cent, normal NaOH. 



Again literature cites many instances to show the influence of acidity 

 and alkalinity upon the bacterial proteolytic enzyme. Wood,' studying 

 proteolytic enz^mies from different bacteria, found that these enzjAmes 

 varied greatly in their power of resisting acid media, and noticed also that 

 the bacteria themselves showed a varying susceptibility to acid, corre- 

 sponding exactly to their enzymes. Fermi ^0 recognized that the enzymes 

 of several bacteria, M. prodigiosus, B. pyocyaneus, Bad. anthracis and 

 others, work most advantageously in faintlj'' alkaline solution, although 

 the}'' attack a solution of gelatin containing 0.5 per cent. HCl. 



Besides these purely physiologic experiments, numerous references may 

 be found in literature which deal with the reaction of culture media upon 

 the morphology and general physiology of bacteria. Fuller ^^ reviewed 

 quite completely the literature of this subject which is treated in his pub- 

 lication. There is indicated a marked influence of media-reaction upon 

 pigment formation, and even upon the morphology, etc., of different 

 bacteria. According to Fuller's publication, moreover, all these investi- 



> Kisch, B. Biochem. Zeitschr., 40, 152, 1912. 



2 Jour. Prakt. Chem., 19, 433, 1879. 



3 Zeitschr. Bakt., 11, 589, 1892. 



* Ann. Inst. Pasteur, 11, 251, 1897. 

 6 Zeitschr. Hyg., 18, 128, 1894. 



• Zeitschr. Hyg., 3, 418, 1888. 

 » Ebenda, 2, 1895. 



8 Arb. kais. Gesundh. Amt., 13, III, 1897. 



» Laboratory Reports, Roy. College Phys., Edinburgh, V, II. 

 '0 Centralbl. f. Bakt., Bd. 16, 176. 1906. 

 1' Jour. Amer. Pub. Health Assn., 1895, 20, 381. 



