A STUDY OF THE VARIATIONS IN HYDROGEN-ION 

 CONCENTRATION OF BROTH MEDIA 



LAURENCE F. FOSTER and SAMUEL B. RANDALL 

 From the Department of Pathology and Bacteriology, University of California 



Received for publication August 15, 1920 



At the present time it would seem scarcely necessary to lay 

 emphasis upon the importance to bacterial growth and metabo- 

 lism of the reaction of the environmental culture medium. That 

 different degrees of acidity and alkalinity in media may pro- 

 foundly influence the morphology, rate of fermentation, pigment 

 production, growth, or viability of bacteria has been so thoroughly 

 recognized that in the routine preparation of culture media as 

 carried on in every bacteriological laboratory, the proper adjust- 

 ment of reaction is carefully regulated. The use of scales of reac- 

 tion such as that of Fuller, based upon adjustment to a definite 

 "degree" of titratable acidity, has permitted a certain amount 

 of uniformity, and in general, it may be said that these old titri- 

 metric procedures have served a very useful purpose. But with 

 the development, diiring the last few years, of the newer physico- 

 chemical conception of hydrogen-ion concentration the theory 

 of titration has undergone a fundamental change. As a conse- 

 quence many of the data obtained in earlier investigations are 

 of little value, having been based upon unsound premises. 



An adequate conception of the far-reaching biological effects of 

 hydrogen-ion concentration may best be gained through a study 

 of the classic works of Michaehs (1914), ^ Sorensen (1912, 1909a, 

 1909b) and Clark and Lubs (1917a, 1917b, 1917c). The fol- 

 lowing statement from the works of the last-named investigators 

 will serve to emphasize the importance to the science of bacteri- 

 ology of this modern conception of acidity and alkahnity: 



1 Bibliography is found at the end of the third article, in this series, p. 231. 



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