26 NUTRITION FACTORS IN YEAST AND BACTERIA 



In summarizing the above results, three points stand out in 

 explanation of the growth stimulating power of the hydrolysates 

 of proteins. 



1) The source of the protein; whether it is obtained from 

 a medium rich in water-soluble vitamine of the B type such as 

 Vitamine D. 



2) The physical structure of the protein and its ability to 

 adsorb vitamine. 



3) The method of purification. 



EXPERIMENTS WITH NEUTRAL SODIUM CASEINATE. 



If these active substances present in casein and three of the 

 other proteins, as described, are nothing more than adsorbed 

 vitamines, and if the protein could be brought into solution with- 

 out subjecting it to hydrolysis, then the vitamine would also go 

 into solution and could be removed by adsorbing it with fullers 

 earth or some other adsorbing agent. 



To test this theory, we prepared a solution of neutral 

 sodium caseinate by suspending our purified casein in water, and 

 adding five percent sodium hydroxide solution until the casein 

 had practically all dissolved. A small amount of insoluble de- 

 natured casein, formed by the action of the alkali, was filtered 

 off, and the solution was then made neutral to litmus. This 

 neutral sodium caseinate solution (containing about 5% casein) 

 was shaken for three hours with ten grams (50 grams per liter) 

 of fullers earth. 



After shaking, the fullers earth was separated from the solu- 

 tion by centrifugation, as filtration was very slow, due to the 

 formation of an emulsion, and the supernatant liquid was then 

 filtered. The fullers earth was repeatedly washed with water 

 and centrifuged to remove small amounts of sodium caseinate 

 adhering to it, pressed out on a suction filter, washed with 

 alcohol and dried. This fullers earth was then extracted with 

 baryta and worked up as described in paper I. 5 The resulting 

 solution was made up to a volume corresponding to a ten percent 

 solution of the original casein, adjusted to a PH of 7.4 and ster- 

 ilized. This solution, when tested, was found to have a strong 

 stimulating effect on the growth of streptococci, but had no 

 action on the growth of yeast cells. 



The neutral sodium caseinate solution, after shaking with 



