Growth-Determining Substances. 225 



different strains of typhoid so that the results cannot be attributed 

 to the idiosyncrasies of one strain. The strains have been plated 

 out repeatedly to see if irregular colonies carrying the lytic prin- 

 ciple could be obtained from the normal culture, but up to the 

 present time no lytic principle has been isolated without the 

 interaction of tissue enzymes with the typhoid bacilli. 



113 (1695) 



Growth-determining substances in bacteriological culture media. 



By J. HOWARD MUELLER. 



[From the Department of Bacteriology, College of Physicians and 

 Surgeons, Columbia University.] 



Some months ago a report was made of a series of experiments 

 based on the observation that, while a peptone-free meat infusion 

 broth would produce abundant growth of hemolytic streptococci, 

 short boiling with charcoal removed this property entirely. The 

 addition of commercial peptone or of a sulphuric acid hydrolysate 

 of certain proteins, such as casein or meat, reactivated the char- 

 coal-treated infusion and heavy cultures of streptococci could be 

 obtained on the mixture, while neither one alone gave the slightest 

 trace of growth. It was shown that the activating material in 

 the protein hydrolysate was precipitated by mercuric sulphate, 

 and that it had not been possible to identify it with any of the 

 amino acids known to be precipitated by this reagent either alone 

 or in combination. It is the purpose of the present communica- 

 tion to describe the further purification of this activating material. 



Much of the work has been done using a commercial prepara- 

 tion called "aminoids" in place of an acid hydrolysate of casein. 

 This consists of an enzyme digest of milk proteins continued until 

 the product is biuret free. It has been used simply as an economy 

 of time since in handling large quantities the acid hydrolysis is 

 somewhat cumbersome. Every step in the separation, however, 

 has been checked on an acid hydrolysate and it is believed that 

 there is no essential difference in the factors involved. 



In attempting to separate the active material from the mercuric 

 sulphate precipitate, fractional precipitation with the same 



