THE RELATION OF HYDROGEN-ION CONCENTRATION 

 TO THE GROWTH, VIABILITY, AND FERMENTATIVE 

 ACTIVITY OF STREPTOCOCCUS HEMOLYTICUS 



LAURENCE F. FOSTER 



From the Department of Pathology and Bacteriology, University of California 



Received for publication August 15, 1920 



I. THE FINAL HYDROGEN-ION CONCENTRATION PRODUCED BY 

 STREPTOCOCCUS HEMOLYTICUS IN BROTH CONTAINING 

 VARIOUS FERMENTABLE SUBSTANCES 



In 1912, Michaelis and Marcora (1912) worldng with a cul- 

 ture of Bad. coli in lactose broth were able to show by means of 

 accurate electrometric measurements, that this organism carries 

 its fermentation of the sugar to a definite level of hydrogen-ion 

 concentration and then ceases its activity. This point is reached 

 regardless of the initial reaction of the medium and can be 

 described as a physiological constant for the particular organism 

 used. This finding was confirmed three years later by W. M. Clark 

 (1915b) ^ who pointed out that the final hydrogen-ion concentration 

 established as a physiological constant by Michaelis and Marcora 

 for a single strain of Bad. coli applied to other strains as well. 

 That the hydrogen-ion concentration of the cultuie, rather than 

 the total acid produced, is the factor limiting activity of the 

 organism seemed evident from the work of Clark. The useful- 

 ness of this so-called physiological constant appeared later as 

 the result of the researches of Clark and Lubs (1915) who sug- 

 gested a method of differentiating the bacteria of the colon- 

 aerogenes group by means of a correlation with gas formation of 

 the final hydrogen-ion concentration produced in glucose broth. 

 In this work was laid the experimental foundation of the methyl 



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



161 



