222 HAROLD C. ROBINSON AND LEO F. RETTGER 



In a medium of ''Casein B" (5 per cent), decolorized and 

 neutral to litmus, the same fourteen pathogens as in the last 

 experiment were inoculated. After forty-eight hours there was 

 no growth of B. diphtheriae (two strains) and of Streptococcus, 

 rather scanty growth of B. abortus (Bang) and B. pseudo-diph- 

 theriae, and good growth with all of the others. Not so many 

 saprophytes as before were used, but all of those that were tried 

 showed abundant growth. 



For the purpose of driving off more of the HCl, some of the 

 ''Casein B " solution was evaporated over a water bath to a thick 

 paste, and as nearly as possible to dryness. Agar was prepared 

 from this paste in the same way as opsine agar, using 1.5 per cent 

 of the paste. On the decolorized agar which was faintly alkaline 

 to litmus B. typhi (I), B. paratyphi A and B, Bad. pullorum, 

 Spir. f inkier-prior , Staph, albus, B. diphtheriae (Y.M.S.), B. 

 acne (51), B. pertussis and a pathogenic yeast found in tubercular 

 sputum grew almost as well as on peptone meat extract agar. 

 Streptococcus (310), B. diphtheriae (D) , Glycobacter peptolyticus 

 and Proteus zenkeri showed only a meagre development, and B. 

 diphtheriae (K.L.) no growth at all. 



These cultures were then kept at 16°C. and subcultures made 

 at different intervals to determine their viability. After five 

 weeks 5. diphtheriae (Y.M.S. and K.L.), B. acne (51), and B. 

 pertussis were found to have died. At eleven weeks all of the 

 others were still alive. 



Effect of decolorization with animal charcoal 



In an experiment to determine whether the decolorizing process 

 had any effect on the nutrient properties, "Casein B" agar was 

 prepared as in the last experiment, one-half of the lot of 

 medium being decolorized. Both the decolorized and unde- 

 colorized agar were inoculated at the same time from young 

 cultures. 



It was found that in general decolorization of the medium 

 detracts little from its nutrient properties. However, B. typhi 

 (lO)and Streptococcus (urine), which grew scantily on the natural 

 medium, failed to grow at all when the latter was decolorized, and 



