ULTRAVIOLET RADIATION— MEIER 375 



experiments he observed that rats on a rachitic diet kept in dark- 

 ness did not develop rickets if they ate the skin of irradiated rats. 

 He therefore concluded that the antirachitic factor could be ab- 

 sorbed with the food and that exposure to sunlight was not necessary 

 as a treatment or prophylactic measure. 



Various scientists have shown that sunlight, natural or artificial 

 (produced by the ultraviolet rays of the quartz lamp), has no effect 

 on starch, mineral salts, and some other products. Only that food 

 which contains fats is subject to the action of sunlight. The activ- 

 able substance in the fat is not the fat itself, but the unsaponifiable 

 part of the butter, a sterol, and the particular variety of sterol is 

 called ergosterol. Ergosterol, when preserved in darkness, has no 

 physiological activity. Only after irradiation with ultraviolet rays 

 does it become antirachitic in a high degree. Ergosterol is extremely 

 active in treatment and prophylaxis of rickets in babies and young 

 children. The treatment is so active that it must be stopped after 

 a month. As a preventative, ergosterol has the same power. In 

 certain countries where there is a lack of sunshine in winter, such 

 as East Prussia, the Government distributes gratuitously vigantol 

 for the new-born and small babies. 



Ultraviolet rays may be used to irradiate babies in order to 

 rectify the lack in their diet of the elements necessary for making 

 bone. This irradiation furnishes vitamin D from the provitamin 

 in the skin. It influences the storage of calcium and phosphorus and 

 their equilibrium in the blood stream of mature animals in a similar 

 way as in growing animals. The antirachitic factor, or vitamin 

 D, is the specific organic agent which promotes normal calcium 

 metabolism. It may prevent and cure rickets, promote growth, or 

 simply prevent excessive loss of lime from the body. 



All the research that resulted in the activation of ergosterol was, 

 so to speak, a combining of old observations on the therapeutic value 

 of fish oils and of light. It has shown that ultraviolet rays acting 

 on the sterol-bearin^ fats of the skin produce a form of vitamin 

 D similar in antirachitic action to the vitamin D contained in fish 

 oils. The vitamin D produced by the irradiation of pure ergosterol 

 has recently been obtained in crystalline form. A recent investigator 

 has found that irradiated cholesterol was many times more effective 

 on chickens than ergosterol that has been irradiated either by itself 

 or in the presence of cholesterol. 



Vitamin D rarely occurs in living plants. The lower plants that 

 are not pigmented and do not make their own food thrive in dark 

 places and perish in the light. The higher plants containing very 

 little ergosterol possess pigments that filter out the activating rays 

 at the short end of the solar spectrum. 



