CULTURAL REQUIREMENTS OF BACTERIA 



319 



meters of each filtrate represented about 0.5 gm. casein. The 

 following media were prepared: 



I Digest of impure casein 12 cc. 

 Water 13 cc. 

 Glucose-salt solution 25 cc. 



I Digest of pure casein '. . . 12 cc. 

 Water 13 cc. 

 Glucose-salt solution 25 cc. 



Control experiments showed that the digest of pure casein was 

 not inhibitory, for the addition of meat infusion produced heavy 

 growth. 



The above experiment was confirmed several times, using 

 difTerent preparations of casein, always with the same result. 

 The conclusion seems warranted that while crude casein contains 

 some accessory substance, this is not a part of the protein mole- 

 cule (and hence probabh^ not an amino acid or polypeptide 

 grouping), and can be easily removed by purification of the 

 protein by standard means. 



Possibility of another source of growth accessory substance free 

 from protein nitrogen 



By the use of the term "accessory substance" in connection 

 with these studies, it is desired to avoid, as far as possible, the 

 conception of vitamines. There is now abundant evidence in 

 the literature that vitamines, particularly the water-soluble 

 vitamine, may be as essential for certain microorganisms as for 

 animals, but there is Uttle probabiUty that the accessory factor 

 or factors of meat infusion is in any way connected with the 

 water soluble vitamine. In the first place, muscle tissue is 

 believed to be low in \dtamine. In the second place, experi- 



