GROWTH OF BACTERIA IN PROTEIN-FREE PRODUCTS 223 



B. diphtheriae (a) and B. pseudo-diphtheriae grew a little less 

 readily after decolorization. The undecolorized cultures were 

 kept fifteen days longer at 16°, and then transferred again to the 

 same medium. All but B. typhi (10), M. catarrhalis and B. 

 diphtheriae (a and 8m) were still alive. The list included the 

 meningococcus, B. avisepticus, B. abortus, M. melitensis and 

 M. cholerae (asiaticae). 



Effect of adding various substances to the digestion products 



When 0.5 per cent Liebig's meat extract was added to '^ Ca'^ein 

 B" media, the growths were quite noticeably increased. Pig- 

 ment production by Staph, aureus and S. aurantiaca was also 

 improved. On agar containing 0.5 per cent meat extract only, 

 growths were scanty and in the case of B. diphtheriae, entirely 

 lacking. 



Since Vedder has claimed that starch is a valuable constituent 

 in culture media, this was also added to '' Casein B" agar to the 

 amount of 1 per cent. No difference in the growth of the organ- 

 isms could be noticed, however. 



Comparisons were made between the following media, all unde- 

 colorized and containing 1.5 per cent agar; (1) "Casein C" 3 per 

 cent, (2) "Casein C" 5 per cent, (3) "CaseinC"7per cent and (4) 

 "Casein C " 2 .5 per cent + edestin product 2.5 per cent + lactal- 

 bumin product 2.5 per cent. On media 1 and 2 the growths were 

 not quite so good as on medium 3. The mixture of 'products 

 proved slightly superior to the other media, Streptococcus and 

 B. diphtheriae (A) growing scantily on this, and not at all on the 

 others. However, the mixture was not so distinctly superior as 

 had been hoped. 



Some of the more difficult organisms to cultivate were also 

 tried out on the following media : 

 I. ''Casein C" 8 per cent. 

 II. Lactalbumin product paste 2 per cent. 



III. "Casein C" 2.5 per cent + lactalbumin product 2.5 per 

 cent + edestin product 2.5 per cent. 



All contained 1.5 per cent agar, were not decolorized, and were 



