24 NUTRITION FACTORS IN YEAST AND BACTERIA 



tained from a medium which we know to be very rich in vitamine, 

 particularly the newly isolated vitamine D. This protein was 

 prepared by heating the filtered autolyzed yeast until the protein 

 had coagulated. As this protein separates in a form similar to 

 milk curd, we see the possibility of great adsorption of vitamines. 

 Although this protein underwent considerable washing, and was 

 suspended in a dialyzing bag for several days, it still retained 

 most of the vitamine which it had originally adsorbed. 



The same is true of casein. This protein, which is precipi- 

 tated by means of dilute acid and is purified by repeatedly 

 redissolving and reprecipitating, separates at the start in the 

 form of a coagulum, and, as other investigators have shown, 

 has great adsorbing powers.* Consequently, no amount of re- 

 dissolving and reprecipitating will entirely free it from vita- 

 mines, as its physical structure and adsorbing properties remain 

 the same. 



With gelatin, we have a somewhat analogous situation. 

 Gelatin, which we prepared in the laboratory, from bones with 

 and without the marrow, was entirely freed from vitamines by 

 the process of purification described by Van Name. 14 This con- 

 sists, essentially, in precipitating the gelatin in absolute alcohol, 

 extracting with ether, redissolving the protein in water, concen- 

 trating the solution to a jelly, reprecipitating in absolute alcohol 

 and again extracting with ether. Commercial gelatin, ("Silver 

 Label" brand) however, contains enough of the active substance 

 to stimulate the .growth of streptoccoci, as we have shown in 

 tables I and II. It seems apparent therefore that the present 

 commercial process for purifying gelatin is not adequate for 

 freeing this protein entirely from the vitamines contained in 

 the bones and parts of the hide that are used. In this connection 

 it might be mentioned that Boyer 15 used an hydrochloric acid 

 extract of finely divided bones for the cultivation of streptococci. 



With edestin, we have a protein which was prepared in a 

 somewhat different manner. We prepared this protein by 

 extracting the ground hempseed with five percent sodium 



The following far-reaching statement was made by Prof. F. G. Hopkins** in his 

 Chandler Lecture given at Columbia University, 1921. "It is remarkable what a considerable 

 portion of the vitamines present in milk is adsorbed by precipitated casein. A failure to 

 recognize this has often obscured the results of feeding trials." 



