INTRODUrTION 741 



Coincident with tlie development of our knowledge of the chemical 

 nature of the antirachitic factor, reports were made as to the therapeutic 

 action of svmlight as a curative agent for rickets. Sniadecki'*^ early in- 

 ferred that sunlight constituted an effective treatment for rickets. In 1890, 

 Palm," on the basis of geographical studies, correlated the incidence of 

 rickets with the degree of sunlight. Cases of human lickets were cured by- 

 artificial light, according to Buchholz,^* while the influence of sunlight on 

 the calcium assimilation of puppies was demonstrated in 1913 by Raczyn- 

 ski.^^ The classical work in this field was carried out in 1919, when 

 Huldschinsky^"^'^^ proved, on the basis of x-ray studies, that severe rickets 

 in chiklren could be cured by irradiation with the quartz mercury vapor 

 lamp. Shortly thereafter, Hess and Unger^^ confirmed the report of 

 Huldschinsky, and also demonstrated the effectiveness of sunlight in pre- 

 venting rickets in rats on a rickets-producing diet.^-^ In 1922, Hess and 

 Gutman'-^ came to the conclusion that the curative action brought about by 

 cod liver oil and by irradiation is essentially the same. 



The reason for the effectiveness of the two methods for the treatment of 

 rickets became evident with the simultaneous discovery in 1924 by Steen- 

 boek and his associates'^ ~-^ and by Hess and co-workers'^ ~^^ that anti- 

 rachitic potency can be conferred upon foods by ultraviolet irradiation. It 

 was realized almost immediately that the precursor of the antirachitic 

 vitamin belongs in the category of provitamins. The active principle was 

 found shortly thereafter to be a sterol-like compound^' "^''^ which, before 

 activation, had no rickets-preventing potency. During the next year 



i« J. Sniadecki, On the Physical Education of Children, Wilno, 1822. Cited by W. 

 Mozolowski, Nature, 143, 121 (1939). 



'' T. A. Palm, Practitioner, 45, 271-279, 321-342 (1890). 



'* E. Buchholz, Verhandl. 21 ten Versamml. Gesell. Kinderhlk., Abt. Kinderhlk., 76len 

 Versamml. dent. Naturforsch., Aerzte, Breslau, 1904, ^1, 116-122 (1905), Wiesbaden. 



'' J. Raczynski, Cotnpt. rend, assoc. intern, pediat., 1D13, 308. Cited by H. R. Rosen- 

 berg, Chemistry and Physiology of the Vitamins, Interscience, New York, 1945, p. 342. 



2»K. Huldschinsky, Deut. med. Wochschr., 45, 712-713 (1919). 



21 K. Huldschinsky, Z. orthop. Chim., 39, 426-451 (1919-1920). 



22 A. F. Hess and L. J. Unger, Proc. Sac. Exptl. Biol. Med., 18, 298 (1921). 



23 A. F. Hess, L. J. Unger, and A. W. Pappenheimer, Proc Soc. Exptl. Biol. Med., 19, 

 8-12 (1921-1922). 



2^ A. F. Hess and M. G. Gutman, ./. Am. Med. Assoc, 78, 29-31 (1922). 



2* H. Steenbock, Science, 60, 224-225 (1924). 



2« H. Steenbock and A. Black, /. Biol. Chem., 61, 405-421 (1924). 



2' H. Steenbock and M. T. Nelson, /. Biol. Chem., 62, 209-216 (1924). 



2s A. F. Hess, Am. J. Diseases Children, 28, 517-521 (1924). 



29 A. F. Hess and M. Weinstock, Proc. Soc. Exptl. Biol. Med., 22, 5-6 (1924-1925). 



«> A. F. Hess and .M. Weinstock, Proc. Soc. Exptl. Biol. Med., 22, 6-7 (1924-1925). 



3' A. F. Hess and M. Weinstock, ./. Biol. Chem., 62, 301-313 (1924). 



32 A. F. Hess, M. Weinstock and F. D. Helman, J. Biol. Chem., 63, 305-308 (1925). 



" H. Steenbock and A. Black, J. Biol. Chem., 64, 263-298 (1925). 



3^ O. Rosenheim and T. A. Webster, Lancet, 1925, I, 1025-1026. 



