GROWTH OF BACTERIA IN PROTEIN-FREE PRODUCTS 213 



bouillon slightly increased the growth of almost all of the organ- 

 isms, but in the acid bouillon it was more often detrimental. 

 This can probably be attributed to the action of acids produced 

 from it by the organisms. In agar the glycerol nearly always 

 appeared to increase the growth slightly. It was also very 

 favorable to intense pigment production. 



The addition of Liebig's meat extract, 0.5 per cent, to neutral 

 opsine agar, yielded considerably better results than the opsine 

 neutral agar alone. The difference between the two was more 

 pronounced at forty-eight hours than at twenty-four. The 

 growths on this extract medium were as a rule almost, or quite, 

 as good as on the common laboratory media. Of course, such a 

 medium would not be protein-free, as Liebig's meat extract has 

 been shown to contain traces of proteoses and peptones. 



Some of the more fastidious organisms grew on a faintly alkaline 

 medium of fresh beef infusion agar -(- 1 per cent opsine almost as 

 well as on meat infusion peptone agar. The following table 

 shows the growths of the third transplants on this medium after 

 thirty hours' incubation: 



Gonococcus (287) + ^ 



Pneumococcus (M) ++ large discrete colonies 



Pneumococcus (697) + ="= small crowded colonies 



Meningococcus (M) + + 



Meningococcus (200) + + =*= 



B. pertussis + + =*= 



B. diphtheriae (Y. M. S.) + + + 



Str. pyogenes ++=^ 



M. melitensis -f- 



When glucose (1 per cent) was added to opsine agar, neutral to 

 litmus, the growths were usually less abundant than on the plain 

 opsine agar. In the case of Streptococcus pyogenes, B. pyo- 

 cyaneus, and B. prodigiosus, however, the reverse was true. Like 

 glycerol, glucose greatly increased and intensified color production 

 by the last two organisms. The inhibition on the part of the 

 glucose was presumably due to acid formation. 



Nitrates were reduced to nitrites in decolorized opsine bouillon 

 by the five strains of B. coli and the one of B. aerogenes 

 tried. The sterile controls were negative. As might be expected 



