DEPARTMENT OF MICROBIOLOGY. 



Part I . 



THE RELATION OF HYDROGEN ION CON- 

 CENTRATION OF MEDIA TO THE 

 PROTEOLYTIC ACTIVITY OF 

 BACILLUS SUBTILIS. 



BY ARAO ITANO. 



INTRODUCTION. 



Since the physico-chemical methods were introduced into the field of 

 biology, the influence of ions, such as Na, Ca, CI, H, upon the vital proc- 

 esses has been increasingly recognized by biologists. This influence is 

 manifested in many phases of biology. In this investigation the relation 

 of the hydrogen and hydroxyl ion concentration, or "true acidity" and 

 "true alkalinity"^ of media, to the proteolytic activity of B. subtilishas 

 been studied. 



The importance of the effect of hydrogen ion concentration of media 

 upon the bacterial growth has been well known to bacteriologists, but it 

 has been impossible to determine the so-called "true reaction." With 

 the introduction of physico-chemical methods, progress toward the 

 measurement of absolute reaction has been made. 



So far as the author knows, Briinn, ^ in 1913, was the first to undertake 

 the investigation of the disinfecting property of acids upon B. coli and 

 B. typhosus. He found that the hydrogen ion concentrations 2X10"^ 

 and IX 10"^ at 37° C. for twenty-four hours have a corresponding germi- 

 cidal effect. Since then, several other investigators have performed 

 similar experiments with the hydrogen ion concentration, emplojang 

 several species of bacteria for their test. The author fails, however, to 

 find that any investigation in the light of hydrogen ion concentration has 

 been conducted on the subject of proteolysis instigated by bacteria. 

 Briinn's experiment illustrates the influence of hydrogen ion concentration 

 upon bacterial life. In other biologic fields, however, considerable work 

 has been done to point out the importance of such an experiment on the 



' " True acidity " and "true alkalinity" are the common terms adopted by S. P. L. Sorensen to 

 express the H and OH ion concentration. 



' Uber das Desinfektionsvermogen der Sauren. Diss., Berlin, 1913. 



