VITAMIN D 297 



children of rickets. Observations by X-ray showed definite calcium 

 deposition after four weeks, with complete healing after eight. He 

 also found (1920) healing of rickets in 30 children after 22 to 26 

 treatments covering 2 months of time. Hess and Unger (1921b) con- 

 firmed this by showing that exposure to ultra-violet light or sunshine, 

 without any modification of the diet would cure infantile rickets. Even 

 though only one wrist was exposed to light, calcification occurred in 

 both, as judged by X-ray and clinical examination. They reported 

 further, that exposure to sunlight prevented rickets in rats on a rickets- 

 producing diet. 



Howland and Kramer (1921) reported that the serum of infants 

 suffering from rickets contains a diminished amount of inorganic phos- 

 phate which, during the process of healing, gradually rises to the 

 normal level; and Hess and Gutman (1922) reported that the cure 

 of rickets by sunlight could be also demonstrated by the rise to the 

 normal level, of the inorganic phosphate of the blood serum. Of this 

 work they said that "it is the first definite evidence of a metabolic 

 change in the animal body brought about by solar rays," and stated 

 it as their belief that the "curative process occasioned by divergent 

 therapeutic agents (cod-liver oil and light) is fundamentally the same." 



In studies on 60 young children, Hess and Lundagen (1922) found 

 a seasonal tide of blood phosphate which could be correlated with the 

 seasonal variation of ultra-violet light waves in the sun's spectrum. 

 They say "these meteorological observations confirm our opinion that 

 the dominating factor in the phosphate tide is sunlight, an opinion 

 which is strengthened by the fact that an increase of blood phosphate 

 was brought about during these winter months simply by irradiations 

 of ultra-violet light from an artificial source. In this connection it is 

 also well to bear in mind that rickets and tetany are almost non-existent 

 in the tropics." 



This view that it is the short light rays which are curative of 

 rickets was confirmed by the finding by Hess, Pappenheimer and Wein- 

 stock (1922) that light waves longer than 334 ^,u are ineffective while 

 shorter than 310 [ifx are effective in preventing rickets in rats on a 

 drastically rickets-producing diet. 



Hess (1925) reported that from June to August rays from the sun 

 as short as 297 fi[x penetrate our atmosphere between 1 1 and 1 o'clock, 

 while from December to February only the longer potent rays, those 

 of about 313 ///i are able to reach us. Hess and Anderson (1927) 

 found that with an equal number of ergs of energy per unit surface area, 

 rays shorter than 290 ,u// were more antirachitic than those between 



