178 MASS. EXPERIMENT STATION BULLETIN 167. 



Part II. 



PROTEOLYSIS OF STREPTOCOCCUS ERYSIPE- 

 LATIS AND STREPTOCOCCUS LACTICUS 

 COMPARED UNDER DIFFERENT HYDROGEN 

 ION CONCENTRATION. 



INTRODUCTION. 



As intimated previously, the methods of proteolysis under different 

 hydrogen ion concentrations as described, might furnish a means for 

 assisting in differentiating closely related organisms. An application is 

 here attempted with Streptococcus erysipelatis and Streptococcus lacticus. 

 The significance of streptococci in market milk, and the indiscriminate 

 practice of attributing many afflictions to them, have led to this choice 

 of organisms, for it involves the so-called virulent and avirulent strains 

 of streptococci. Heinemann ^ and others have demonstrated that Strepto- 

 coccus lacticiis is very closely related to Streptococcus pyogenes, not only 

 morphologically and culturally, but also in pathogenicity. 



GENERAL METHODS OF PROCEDURE. 

 Organisms employed in the Investigation. 

 (a) Streptococcus Erysipelatis (Streptococcus "E "). 

 Furnished by H. K. Mulford Company, Philadelphia. Virulent for 

 rabbit. Guaranty No. 172. 



(6) Streptococcus Lacticus. 

 Isolated by the author from starter at this institution and found to be 

 avirulent for rabbit. 



Medium. 

 Composition: — 



500 gms. chopped lean beef - 1 



1 per cent. Witte's peptone > per 1,000 c. c. of water. 

 0.5 per cent. NaCl J 



' Heinemann, P. G. Jour. Infect. Diseases, 4, No. 1, 89, Jan., 1907. 



* Chopped lean beef, rather than Liebig's meat extract, was found to be favorable for this 

 investigation. 



