IV. UNIDENTIFIED VITAMINS 

 AND GROWTH FACTORS 



BY KARL FOLKERS' 



THERE are many investigations in progress which are concerned 

 with the elucidation of new vitamins and growth factors. 

 These investigations include nutritional experiments with ani- 

 mals, poultry, microorganisms, insects and other forms of life. Because 

 of the magnitude of the literature on unidentified vitamins and growth 

 factors, it seemed best for this review to select the results of certain 

 investigations for discussion. 



Experience has shown that the initial phases of certain nutritional 

 investigations can be quite independent and diverse, and yet the final 

 phases may be the same. 



Turning to the past, an excellent example of initially diverse nutri- 

 tional investigations was the independent researches on coenzyme R 

 which was described as a growth and respiration promoting factor for 

 Rhizohium trifolii, on biotin which is a yeast-growth factor, and on 

 vitamin H which was a factor for rat nutrition (Table I). 



In the final phase of these investigations, it was concluded that these 

 three independent researches on the nutrition of Rhizohium trifolii, 

 yeast, and rats were concerned with a single entity — biotin. 



Turning to the present, it is desirable to discuss first folic acid and 

 possible chemically related factors. These factors appear to deserve 

 mention first for several reasons. The chemistry of the first members of 

 the group to be elucidated is now becoming available. All the members 

 of this group are receiving much study at present in many laboratories. 

 These factors as a group typify again the development of independent, 

 but frequently converging lines of nutritional studies. 



These factors were introduced into the literature by such designations 

 as vitamin M which is a factor for cytopenia in monkeys ; norite eluate 

 factor for the growth of L. casei; vitamin Be for a microcytic hyper- 

 chromic type of anemia in chicks ; factor R for chicks ; folic acid for the 

 growth of S. lactis and L. casei; liver L. casei factor; Streptococcus 

 lactis R factor ; vitamins Bio and Bn for chicks ; fermentation L. casei 

 factor; and the vitamin Be conjugate. The early papers on these factors 

 (Table II) appeared during 1938-1945. 



1 Research Laboratories, Merck & Co., Inc., Rahway, N.J. 



