Abstract
The flavins 6-ethyl-7-methyl- and 6-methyl-7-ethyl-9-(1′-D-ribityl)isoalloxazine have been found to be indistinguishable from riboflavin in the nutrition of Lactobacillus casei when either is the only flavin available to this micro-organism throughout limiting concentration ranges. These two flavins are also able to satisfy the requirement for a flavin in the growth and survival of the rat. The 6-ethyl-7-methyl-flavin and the 6-methyl-7-ethyl-flavin have 47 and 36%, respectively, of the activity of riboflavin for growth of this animal. These two flavins can not be considered as completely adequate replacements for riboflavin in the nutrition of the rat, however, since they are unable to satisfy the need for a flavin in the over-all function of reproduction in this animal.