UNIDENTIFIED VITAMINS 87 



That fraction of aqueous liver extract which was insoluble in 70% 

 alcohol ("Fraction A"), yeast extract (Difco), and rice bran extract 

 (Vitab) were good sources of the active factor. It appeared that this 

 factor was not a known amino acid, since the organisms did not grow 

 even when the amount of casein hydrolyzate in the medium was in- 

 creased to one per cent. 



It was found that the factor in liver "Fraction A" was not readily 

 dialyzable, but some of the purified concentrates contained the factor 

 in dialyzable form. Treatment of the liver "fraction A" with alcoholic 

 hydrochloric acid converted the non-dialyzable form of the factor into 

 a dialyzable form. 



A "maximal unit" for the assay of this factor was defined as the 

 amount of material per cubic centimeter of the medium which was re- 

 quired to produce the maximal growth and acidity. 



The purification procedures yielded concentrates which showed 

 I m.u./ioy. The factor was not soluble in acetone, chloroform, or ethyl 

 acetate, and was not readily adsorbed on norite. 



Pollack and Lindner showed that a substance was present in peptone 

 which was necessary for the growth of L. casei, and Smith showed that 

 certain strains of S. lactis grew better with a substance present in 

 yeast and peptone. It appeared to Sprince and WooUey that their factor, 

 strepogenin, was probably responsible for the growth phenomena ob- 

 served by Pollack and Lindner for L. casei and by Smith for S. lactis. 

 Sprince and Woolley prepared three concentrates of strepogenin by 

 dissimilar methods (dialysis, alcoholic butylamine extraction, and par- 

 tial hydrolysis of casein, etc.). Each of the three concentrates was as- 

 sayed for per cent recovery of activity by testing it for the growth of 

 the hemolytic Streptococcus X40, L. casei and S. lactis. It may be seen 

 from these per cent recoveries of activity that the active substance was 

 recovered about equally for these three organisms. Sprince and Woolley 

 concluded that the same substance, or very closely related substances, 

 were responsible for the growth activity in each case (Table XIX). 



Since Wright and Skeggs had found strepogenin-like activity for 

 enzymic digests of casein, Sprince and Woolley treated purified proteins 

 with trypsin and examined the digests for strepogenin activity by assays 

 with L. casei (Table XX). 



The relative strepogenin contents of several such proteins showed 

 that many of them are much richer sources of this growth factor than 

 is the liver fraction L. Crystalline trypsinogen and insulin were out- 

 standing in having 30-40 times as much strepogenin as liver fraction L. 



