THE VITAMINES IN THE VEGETABLE KINGDOM 63 



remains in the decolorized beef-heart infusion and two others which 

 were found in the hydrolyzate of the commercial casein preparation 

 "aminoids. " Of the latter two, the substance "x" was detected 

 in the silver sulphate precipitate and the substance "y" in the fil- 

 trate. In collaboration with Freedman (167c), we were able to 

 show that not all p\ire proteins (hydrolyzed) fulfill the nutritional 

 requirements of Streptococcus hemolyticus. As a rule, purification 

 of these proteins diminished their nutritive value for these bac- 

 teria. Other proteins obtained from sources rich in vitamines 

 are with great difficulty, or not all, freed from this growth substance. 

 On the other hand, this growth substance can be adsorbed in a way 

 similar to vitamines, since fuller's earth and norit remove it from 

 autolyzed yeast, hydrolyzed casein and a neutral solution of sodium 

 caseinate. This phenomenon will permit of further investigation. 

 The absence of the growth substance from a number of purified 

 proteins of various sources renders it unlikely that the above growth 

 factor is an integral part of the protein molecule. It is more than 

 likely that the growth substance is similar to that necessary for 

 yeast and found in the same starting material the only dis- 

 crepancy being that those hydrolyzed proteins which act on strepto- 

 coccus do not act upon yeast. However, this might easily be a 

 matter of inhibition due to the various protein cleavage products. 

 In this connection, Norris (167d) found that casein was a better 

 medium than brewer's yeast for culture. 



The many points brought out in this small chapter, touching in 

 particular upon the physical characteristics of the substances which 

 act on bacteria, form, for the time being, the sole criterion for their 

 classification in the group of vitamines. By comparing the char- 

 acteristics here set forth with the description of the vitamines to 

 follow later, the reader will have the opportunity of making a decision 

 for himself as to which group these substances should be assigned. 

 Looking upon this chapter as a whole, we may conclude that at least 

 some types of bacteria respond to the addition of vitamine with 

 accelerated growth, showing possibly that a small initial quantity of 

 vitamine suffices to render the bacteria independent of any further 

 vitamine additions for a long time. As we shall see in the chapter 

 on the growth of higher plants, bacteria seem to exist entirely inde- 

 pendent of any vitamine supply. According to our present knowl- 

 edge, these are the bacteria which supply the whole organized world 



