STREPT. ERYSIPELATIS AND STREPT. LACTICUS. 185 



4. Alteration of the hj'drogen ion concentrations toward the optimum 

 occurred during the course of proteolysis. 



These results for Streptococcus erysipelatis and Streptococcus lacticus 

 point to a very close relationship between the optimum hydrogen ion 

 concentration for proteolysis (in the bouillon) and the hydrogen ion con- 

 centration of their natural environmental conditions (blood and milk, 

 respectively). 



So far as this investigation is concerned, the differentiation of Strepto- 

 coccus erysipelatis and Streptococcus lacticus, virulent and avirulent strepto- 

 cocci, through their proteolytic activity in conjunction with certain hy- 

 drogen ion concentration in culture medium, seems to be promising, 

 although further data are desired before its generaUzation may be realized. 



In connection with tliis investigation, the author's gratitude is due to 

 Prof. S. P. L. Sorensen, Prof. A. Klocker, Dr. H. Jessen-Hansen and Dr. 

 Sven Palitzsch, of the Carlsberg Laboratory, Copenhagen, Denmark; to 

 Prof. A. Hopkins of Amherst College; to Prof. J. S. Chamberlain and 

 Prof. F. H. H. van Suchtelen of this institution; especially to Prof. C. E. 

 Marshall, under whom the work of this thesis has been concluded. 



