162 VITAMIN D GROUP 



such foods as fish and eggs, the vitamin must normally be obtained by ex- 

 posure of the body surface to the sun (the "sunshine vitamin"). Since 

 sunshine is variable, both daily and seasonally, the amounts obtained 

 by insolation vary widely. The body has two mechanisms for adjustment 

 to the variable supply. Excess vitamin D is stored, principally in the liver, 

 where it may be held and released over long periods of time. This is the 

 basis of the "Stosstherapie" method of preventing rickets in children, 

 which consists in administering massive doses of vitamin D at intervals of 

 several months.^**' ^^^ Prolonged insolation results in tanning, a process of 

 temporary pigmentation which presumably has the effect of filtering out 

 the activating rays received in superabundance. It is well known that 

 Negroes and other dark-skinned people are more susceptible to rickets than 

 white people, and this difference appears to be due at least in part to pig- 

 mentation.^^*- ^*® The picturesque suggestion has been made that in human 

 evolution vitamin D played a role in the appearance of blonde races in the 

 cold countries, where they have an advantage over dark races in the ab- 

 sorption of the limited sunlight. 



That man and animals are well adapted to a variable supply of vitamin 

 D is clearly shown in the phenomenally wide margin which exists between 

 the therapeutic and the toxic doses of this substance." For rats, doses 1000 

 times the antiricketic dose, administered daily for months, are just per- 

 ceptibly harmful, and much larger single doses can be tolerated. For man, 

 the margin appears to be somewhat less, but still enormous. Probably no 

 other potent therapeutic agent exhibits such a wide margin of safety, but 

 if it were not wide, animal life could not have survived the fluctuations in 

 solar activity and vitamin D formation to which it has always been sub- 

 jected in nature. 



The formation of vitamin D on the body surface has been thoroughly 

 studied. Sunshine, like fish oil, is an old remedy for rickets. In 1919 Huld- 

 schinsky^" clearly demonstrated, by means of radiographs, the healing ac- 

 tion of sunlight and of the light from the quartz mercury arc. Hess ei al}^^ 

 determined that the effective wavelengths of light are the shorter ultra- 

 violet waves of the solar spectrum, or the still shorter waves of artificial 



1" G. O. Harnapp, Wien. klin. Wochschr. 53, 698 (1940). 



>" H. Uflacker, Z. Kinderheilk. 67, 350 (1949). 



•" A. F. Hess, Rickets, Osteomalacia and Tetany, p. 92. Lea and Febiger, Phila- 

 delphia, 1929. 



is«M. M. Eliot and E. A. Park, in Brennemann's Practice of Pediatrics, Vol. 1, 

 Chapter 36, pp. 3, 12. W. F. Prior Co., Hagerstown, Md., 1948. 



1" K. Huldschinsky, Deut. med. Wochschr. 45, 712 (1919); Z. orthopdd. Chir. 38, 426 

 (1920). 



'68 A. F. Hess, A. M. Pappenheimer, and M. Weinstock, Proc. Soc. Exptl. Biol. Med. 

 20, 14 (1922). 



