RADIATION AND VITAMINS 333 



The products of extreme overirradiation, presumably the end products 

 of the series, were designated Suprasterine by Windaus, Gaede, Koser, 

 and Stein (95). They recognized two isomers, suprasterol I and supra- 

 sterol II, which they separated by taking advantage of differences in the 

 solubiHty of the allophanic acid esters. The suprasterols are not anti- 

 rachitic and are only slightly toxic. 



In the review by Bills (9) a mass of evidence was summarized which 

 goes to show that ergosterol, lumisterol, and tachysterol are not the only 

 sterols which become antirachitic upon irradiation. They are, however, 

 the supremely important ones, and the only ones which develop enormous 

 antirachitic potency. It was also brought out that several forms of 

 vitamin D exist, which differ from each other in physiological action. 

 Thus, for example, the vitamin D as ordinarily prepared from ergosterol 

 is far more effective for rats than for chickens, while the reverse is true 

 of the vitamin D contained in fish oils. 



ORIGIN OF VITAMIN D IN NATURE 



Vitamin D rarely, if ever, occurs in living plants, and the reason is 

 not difficult to understand. The lower, nonpigmented, nonphotosyn- 

 thesizing plants, which contain much ergosterol, thrive in dark places and 

 perish in the light. The higher plants, containing relatively little 

 ergosterol, possess pigments which presumably filter out the activating 

 rays at the short end of the solar spectrum. Even if the vitamin could 

 be formed in the superficial layers, plants could not store it, "unprovided 

 as they are with any system for the translocation of lipoids." Dead 

 plant tissue, by insolation, may acquire slight potency, as in the case of 

 hay cured in the sun, coconut oil rendered by solar rays, or mushrooms 

 struck by sunlight. Lack of color is no indication of the activatability 

 of plant materials, for even such tissues as white iris petals are known to 

 contain filters against ultra-violet rays. 



In the animal kingdom vitamin D is widespread, but abundant only 

 in the fishes. Its origin in fishes is obscure. Steenbock and Black (82) 

 suggested that it is formed by the insolation of plankton which in turn is 

 ingested by Uttle fish, and these by larger fish, etc. Against this hypothe- 

 sis is the observation by Leigh-Clare (53) that the marine diatom, 

 Nitzschia closterium, which synthesizes "vitamin A," fails to effect any 

 genesis of vitamin D, even when grown under conditions of maximum 

 insolation. Drummond and Gunther (24) obtained essentially negative 

 findings with both phytoplankton and zooplankton collected from the 

 ocean. Belloc, Fabre, and Simonnet (7) found that zooplankton collected 

 in spring contained ergosterol but no vitamin D, while zooplankton 

 taken in midsummer showed ergosterol with perhaps vitamin D. Their 

 evidence, although not convincing, may have some significance in view 

 of the July change in vertical distribution of zooplankton (Russell, 74). 



