V. STANDARDIZATION OF ACTIVITY 99 



weighing 40 to 50 g. are assembled in groups of twelve and fed a \itamin 

 A-frec diet for 6 days. The stored vitamin A reserve is said to be used up in 

 that time. Then for 2 days, the animals of one group are fed the sample to 

 be tested antl another group is fed a vitamin A standard preparation. After 

 another 2 days the animals are killed and the vitamin A content of the 

 liver determined. "** 



In 1940 Ir\'ing and Richards"^ described a biological method of assay 

 which uses in a prophjdactic test the histological changes of the medulla, 

 caused by vitamin A deficiency. This method is rather sensitive and is 

 regarded to be very reliable by Goetzee/-" so long as the sex is taken into 

 consideration. Male rats require approximately 1.5 times as much vitamin 

 A as females of the same age in order to overcome the symptoms of defi- 

 ciency. 



V. Standardization of Activity 



H. H. INHOFFEN and H. POiVIMER 



Improvements of the biological, chemical, and physical assay methods, 

 and the abundance of knowledge involved, brought about a re\dsion of the 

 international vitamin A standard' (for information on the development of 

 the vitamin A standards, see Morton^). The conference of the expert 

 Committee on Biological Standardization, World Health Organisation, in 

 1949 in London, recommended new international standards.^ According to 

 the new proposals, the old /3-carotene standard' was retained as reference 

 standard for pro\dtamin A but not for vitamin A. Thus, one international 

 unit (I.U.) of provitamin A is equivalent to 0.6 7 of /3-carotene. A new 

 standard was fixed for vitamin A. The test substance selected was vitamin 

 A acetate, which is easily obtained in a crystalline and pure state and shows 

 sufficient stabilitj^ on storage in the cold and in vacuum.^ An international 

 unit of vitamin A is equivalent to 0.344 7 of vitamin Ai acetate (0.300 7 of 

 vitamin A alcohol) . This standard was fixed after careful statistical evalua- 



"8 W. D. Gallup and J. A. Hoefer, Ind. Eng. Chem. Anal. Ed. 18, 288 (1946). 

 "9 J. T. Irving and M. B. Richards, Biochem. J. 34, 198 (1940). 

 120 W. H. R. Goetzee, Biochem. J. 45, 628 (1949). 

 1 Report of the Conference on Vitamin Standards, Geneva, 1931; League of Nations 

 Publication, C. H. 1055 (1); Second Conference on Vitamin Standardization, 

 Quart. Bull. Health Organisation League Nations 3, 428 (1934). 

 * R. A. Morton, J. Pharm. and Pharmacol. 2, 129 (1950). 

 3 World Health Organization Tech. Kept. Ser. 30, 1-7 (1950). 



■* N. B. Guerrant, M. E. Chilcote, H. A. Ellenberger, and R. A. Dutcher, Anal. 

 Chem. 20, 465 (1948). 



