DIET AND NUTRITION 



reduces the content of phosphorus in the blood. The 

 provision of vitamin D tends to regulate the calcium and 

 phosphorus metabolism so as to keep the blood at a normal 

 concentration as respects these elements. 



While vitamin D occurs in abundance only in cod liver 

 oil, and to a lesser extent in egg yolk, the mother substance 

 of it, ergosterol, occurs w^idely distributed in plant prod- 

 ucts. It is most abundant in the fungi and was originally 

 discovered in the oil of ergot. Ordinary yeast contains 

 about 0.15 of 1 per cent on a dry basis, but may be culti- 

 vated under conditions where much higher yields are 

 obtained. Ergosterol is chemically a sterol related to 

 cholesterol, vv^hich is a component of every living cell 

 and is especially abundant in nerves and brain. Ergosterol 

 is a w^hite crystalline substance vs^hich, when administered 

 to a rachitic infant or rat, exerts no beneficial effects if the 

 substance is kept in subdued light. If, however, the 

 ergosterol has been exposed for a brief period to a source 

 of ultra-violet rays, it is activated or changed into vitamin 

 D. Only wave lengths between 265 and 313 microns are 

 effective in activating ergosterol. This discovery constituted 

 the first demonstration that a vitamin is a chemical sub- 

 stance. Activated ergosterol is now prepared in large 

 amounts and is marketed dissolved in some vegetable oil 

 which is palatable and does not easily grow rancid. The 

 commercial product is known as Viosterol and is, to a 

 considerable extent, now being prescribed by physicians 

 instead of cod liver oil. It is recognized, however, that the 

 diet of the child must provide a liberal amount of vitamin 

 A in order to make Viosterol therapy equivalent to cod 

 liver oil therapy, since cod liver oil is rich in both A and D. 



The discovery of ergosterol and its activation by ultra- 

 violet rays explains the relation of climate to rickets. 

 Rickets has been rare in the Tropics because there people 

 expose a considerable area of their skin to a sunlight rich 



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