VITAMIN D 301 



Steenbock and Black (1924) irradiated diets of purified food ma- 

 terials, thus "making them growth-promoting and bone calcifying to 

 the same degree as when rats are irradiated directly." . . . "The ques- 

 tion now presents itself, are we justified in making the further assump- 

 tion — that the acceptance of the existence of an antirachitic vitamin 

 upon its former premises is no longer justifiable, granted, of course, 

 that we accept a vitamin as a compound of biological origin. If such 

 were justified it would simplify our conceptions materially because it 

 has been difficult though not impossible to conceive how two such 

 apparently different agencies, light and vitamin, should have the same 

 effect. It suggests itself that, in ultimate analysis, both light and the 

 antirachitic vitamin may represent the same antirachitic agent — possibly 

 a form of radiant energy. In this connection it is of interest to mention 

 that the authors have conferred growth-promoting properties upon olive 

 oil and lard by irradiation with ultraviolet light." 



Steenbock and Nelson (1924) presented histological evidence to 

 show that a ration which induces rickets in a rat can be made definitely 

 antirachitic by the simple expedient of exposing it to ultra-violet light. 

 In this paper they emphasized their belief "that in the study of the 

 fundamental causes of rickets too much emphasis has been placed 

 heretofore upon the production of the histological picture of rickets 

 characterized primarily by the over production of osteoid and the dis- 

 orderly occurrence and arrangement of various bone elements in a wide 

 metaphysis. This is produced by a peculiar combination of factors as 

 yet imperfectly understood except that growth is a prerequisite for 

 its production. Physiologically, however, there is operative here, among 

 other factors, the same agency which is responsible for the failure of 

 assimilation of calcium in the mature goat (J. Biol. Chem. 14, 59; 53, 

 21; 58, 43) in the growing chicken (J. Biol. Chem. 52, 379; 58, 33) 

 and in the pig (unpublished data) as observed in this laboratory; and 

 that agency is radiant energy either acting directly upon certain com- 

 pounds in the animal body or else acting indirectly through food ma- 

 terials ingested." 



A full account of the experiments upon which Hess had reported 

 in June 1924 was published in December 1924. Hess and his coworkers 

 stated that their first definitely favorable result was obtained when 

 they used irradiated cottonseed oil, 0.1 cubic centimeter daily of which 

 was protective in spite of a severe rickets-producing diet. Other oils 

 were similarly tested. Linseed oil, lettuce and growing wheat plants 

 were successfully activated. The authors concluded that it could not 

 "be definitely stated that it is the same factor which gives codliver 



