VITAMIN G (Bo) 131 



unaffected until 9 to 13 weeks of age, by which time the animal had 

 attained a body weight of 100 to 130 grams. No symptoms of ill health 

 were found in rats observed 3 to 4 months after growth had become 

 subnormal. These findings indicate the non-identity of the "antipel- 

 lagric" and a second heat-stable growth factor, or in other words, the 

 existence here of another mammalian growth essential beyond vitamin G. 



Salmon, Hays and Guerrant (1928) also reported that certain dis- 

 crepancies observed in their laboratory point to the non-identity of the 

 "pellagra-preventing" factor and some factors other than vitamin B 

 (Bi) needed for growth. WilHams and Eddy (1929) are studying this 

 problem by examining the physiological properties of various prepara- 

 tions made by fractioning an autolyzed yeast extract. 



Each investigator must assure himself that no factor other than 

 vitamin B (Bg) is limiting growth in experiments designed to measure 

 vitamin G (B2) potency. This may be done either by incorporating 

 these additional factors in the basal diet, or by limiting the experimental 

 period to that time during which the bodily store of these additional 

 factors suffices to maintain the desired rate of gain. So far as can be 

 judged from the available evidence, the bodily store of these additional 

 factors usually far exceeds the store of vitamins B and G. Studies on 

 the problem of amply insuring the basal diet in these factors are in 

 progress. Until this can be accomplished the term vitamin G (B2) may 

 occasionally designate not a single substance, but the mixture of factors 

 differentiated from the antineuritic vitamin but not yet fully differenti- 

 ated from each other. 



Quantitative measurement of vitamin G (B2) by the rat-growth 

 method requires supplementing a basal diet free from all water-soluble 

 vitamins with a source of the relatively heat-labile factors compara- 

 tively deficient in the water-soluble, more heat-stable factors. Chick 

 and Roscoe (1927) found Peters' antineuritic concentrate (Peters 1924; 

 Kinnersley and Peters 1925) to be such a product. They used the 

 fraction obtained by extracting with 50 per cent acidified alcohol the 

 charcoal concentrate made from an aqueous yeast extract previously 

 treated with lead acetate, mercuric sulfate and hydrogen sulfide. This 

 preparation was concentrated at a low temperature under reduced 

 pressure, and the residue was taken up in water so that 0.1 cubic centi- 

 meter corresponded to 0.6 gram of dry yeast, an amount which they 

 found amply sufficed for the daily needs of the rat for vitamin Bj. 



Evans and Burr (1928c) used tikitiki, a dilute-alcohol extract of 

 rice polishings, as a source of the antineuritic vitamin with little of the 

 other water-soluble growth-promoting vitamins. 



