370 RIBOFLAVIN 



of riboflavin, are present in adequate amounts. The numerous diets which 

 have been used since the original Bourquin-Sherman diet have been tabu- 

 lated by Day and Darby, ^^ and the details of the biological assay are dis- 

 cussed by these authors. The diets have been made more complete with 

 the passage of time, the availability of more crystalline vitamins, and more 

 knowledge of the rat's nutritional requirements. Undoubtedly further im- 

 provements could now be made. 



The usual assay is made with weanling rats which are fed the riboflavin- 

 low diet for 2 or 3 weeks until growth has practically ceased in the majority 

 of the animals. They are then carefully divided according to weight, sex, 

 etc., and groups are fed various levels of the test material. Other groups 

 receive standard amounts of riboflavin. At the end of the test period the 

 growth of the standard groups is used to construct a dose-response curve 

 from which the riboflavin content of the unknown is determined. Bliss and 

 Gyorgy^^ and Day and Darby^* have discussed these assays and the calcu- 

 lation of results in detail. Assays utilizing young chicks have also been 

 used^^ • ^* in which the general procedure is similar, although the diet must 

 be devised with the nutritional requirements of chicks in mind. 



It is commonly assumed that the bioassay which utilizes larger animals 

 has peculiar advantages over other methods, since it measures the response 

 of the vitamin in an organism similar to man or at least more similar than 

 is L. casei. It may be well to point out that this is not necessarily so. There 

 is ample evidence that the response of the rat to known amounts of ribo- 

 flavin is markedly influenced by the composition of the diet with which it 

 is fed. Specifically, the amount and kind of carbohydrate and fat are known 

 to be important,^^ and other unsuspected relationships may exist. The level 

 of these may not be controllable when low-potency materials are assayed. 

 Thus one reaches the same position found in all assays to date, namely that 

 accurate figures for low-potency materials may probably not be obtained. 

 Furthermore, it would appear logical that these and other dietary inter- 

 relationships will be true of the human species as well. If so, the riboflavin 

 potency of a given material will vary with the diet with which it is fed as well 

 as with the composition of the material itself. This rather unsatisfactory 

 state of affairs must be accepted as the nature of the thing, and the bioassay, 

 even if accurately done, appears to offer no advantages except for research 

 studies on the physiology of riboflavin. The more rapid and accurate 

 methods discussed elsewhere should, and undoubtedly will, be favored. 



5' P. L. Day and W. J. Darby, in Biological Symposia, Vol. XII, Estimation of the 



Vitamins. Jaques Cattell Press, Lancaster, Pa., 1947. 

 ^2 C. I. Bliss and P. Gyorgy, in Vitamin Methods, Vol. II. Academic Press, New 



York, 1951. 

 " T. H. Jukes, ./. Nutrition 14, 223 (1937). 

 " G. J. Mannering, D. Orsini, and C. A. Elvehjem, J. Nutrition 28, 141 (1944). 



