258 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



Values for vitamin-A, vitamin-Bi, and vitamin-C content of foods 

 and other materials determined prior to the adoption of the Inter- 

 national Standards of Reference are for the most part expressed in 

 terms of the Sherman units. For some foods the only values avail- 

 able are expressed in these units and for this reason attempts have 

 been made to derive factors showing the relation between the Sher- 

 man and the International units. Since there has been some divided 

 opinion as to what these should be, it seems well to reemphasize the 

 fact that a biological unit does not have an exact value. These 

 units are defined in terms of animal behavior which, however well 

 controlled, is certain to vary. This simply means that the ratio be- 

 tween an International unit and the corresponding biological unit 

 varies according to conditions, and a fixed figure cannot be estab- 

 lished for it. Values expressed in International units which have 

 been derived from Sherman unit values by use of conversion factors 

 cannot be considered more than rough approximations. International 

 unit values so obtained should be clearly designated if pre- 

 sented with other material. The ratios given below for these two 

 units represent general experience with comparative values. 



Suggested Interrelation of Sherman Units for Vitamvrts A, B, C, and O and the 

 Corresponding International Units 



Vitamin A. — Sherman units of vitamin A corresponding to 1 International unit 

 of vitamin A have been found to vary from 0.8 to 2.5. The ratio of 1.5 is 

 suggested as most representative, that is, 1 Sherman unit of vitamin A=0.7 

 International unit. 



Vitamin Bi. — Sherman unit values of vitamin Bi corresponding to 1 Inter- 

 national unit of vitamin Bi have been found to vary from 0.7 to 4 or 6 Sherman 

 units. The most general relation for the majority of values obtained by the 

 Sherman technique is suggested as 1 Sherman unit equivalent to 1 International 

 unit. 



Vitamin C. — One Sherman unit of vitamin C is generally considered equivalent 

 to 10 International units. 



Riboflavin. — One Sherman-Bourquin unit of vitamin G is equivalent to 3.0 

 to 3.5 micrograms of riboflavin. 



VALUES FOR THE VITAMIN" CONTENT OF FOODS 



For some purposes, and especially for dietary calculations, it is 

 desirable to have a set of values showing the quantities of the vari- 

 ous vitamins in different foods. In the general discussion of food 

 sources of the vitamins it was made clear that no food has a fixed 

 and invariable content of any vitamin. Values for different samples 

 of any food may vary over wide ranges depending upon the factors 

 that influence the content of the vitamins it contains. The deriva- 

 tion of average values, in the strict sense of this term, is not possible 

 without using an unreasonable amount of descriptive material con- 



