VITAMIN G {B2) 129 



from B (Bi) as follows: "Fraction Bi is adsorbed on silica gel at pH 3. 

 The filtrate is rich in vitamin B2, but still contains some vitamin Bi. 

 By precipitation with acetone a material is obtained of which daily 

 doses of 0.015 gram in addition to 0.0002 gram of Bi, both added to 

 the standard diet, suffice to maintain normal growth of white rats. By 

 repeating the extraction six times, a material is obtained from the 

 filtrate of which daily doses of 0.005 gram are required. Finally, when 

 this material is dissolved in water and precipitated with alcohol con- 

 taining 1 per cent of hydrochloric acid, a material is obtained of which 

 daily doses of 0.0007 gram suffice to maintain normal growth of white 

 rats." 



Quantitative Determination of Vitamin G 



When experimental animals used in vitamin research attain normal 

 growth, it must be remembered that the nutritional essentials con- 

 sciously provided in the basal diet may be supplemented (a) by un- 

 recognized constituents in the basal diet or (b) in the test materials 

 carrying the particular factor directly under observation, (c) by bodily 

 reserves of the experimental animal, or (d) by a combination of these. 

 Sudden and marked changes in the rate of growth, unequal effects upon 

 growth of doubling the vitamin intake from different source materials, 

 and supplementary effects in growth-promoting values of two materials 

 are some of the indications that the basal diet is not complete qualita- 

 tively or quantitatively in all of the nutritional essentials other than the 

 factor under consideration. 



In the fractionation of the vitamin B complex it has become increas- 

 ingly evident that the effects formerly ascribed to "water-soluble B" 

 are due to more than two chemical entities. 



Possible Interfering Factors in Vitamin Determinations. — In studies 

 conducted before the report of Steenbock, Sell and Nelson (1923) to 

 the effect that coprophagy diminished by half the apparent vitamin B 

 requirements of rats. Palmer and Kennedy had used, with good results, 

 a hot alcoholic extract of wheat embryo as a source of the water-soluble 

 vitamins. But in papers published in 1927 and 1928 they pointed out 

 that when coprophagy is prevented and a highly purified casein serves 

 as the source of protein, this ration fails to support the growth of young 

 rats for more than six or seven weeks, or the maintenance of adults 

 except for a few^ weeks. They believe that this ration contains sufficient 

 of both vitamins B and G inasmuch as it is not improved by the addition 

 of Osborne and Wakeman's yeast concentrate "fraction II," Harris 

 yeast powder, or by a cold alcoholic extract of yeast. The facts that 



