BIOLOGY IN HUMAN AFFAIRS 



in ultra-violet rays. These rays are sufficiently penetrating 

 to activate the ergosterol in the skin and so to protect the 

 development of the bones. Peoples in the Far North, who 

 also escape rickets, do so because they take vitamin D in 

 the oils of marine origin, eggs, etc. 



Vitamin E. There is w^idely distributed in vegetable 

 products a substance which has been shown to affect 

 reproduction in the rat. Female rats deprived of this 

 substance exhibit normal oestrus, ovulation, copulation, 

 and implantation. In gestation where E is insufficient or 

 absent, the embryos at first appear normal but show 

 retardation in development by the eighth day or soon 

 thereafter. There is no detectable abnormality of structure, 

 but sometime between the twelfth and twentieth day 

 foetal death occurs, usually on the twelfth or thirteenth. 

 The maternal placenta is not altered structurally sufficiently 

 to indicate that its function is impaired. In males kept 

 on an E-free diet, sterility develops after about the seven- 

 tieth day. Spermatogenesis ceases and spermatozoa are 

 replaced by spermatids. Sterility in the male once developed 

 is permanent. The testes of such rats undergo a slow 

 progressive desquamation and degeneration of the germinal 

 epithelium involving chromolysis, plasmolysis, pycnosis, 

 giant-cell formation, karyolysis and karyorrhexis of the 

 germ cells followed by lipoid degeneration, granular 

 liquefaction, and final dissolution of the cells. 



Vitamin E is soluble in fats and is most abundant in the 

 oil of wheat germ. Apparently all cereals and leafy vege- 

 tables, and probably root vegetables as well, contain a 

 considerable amount of this principle. 



Vitamin G. Pellagra was not recognized in the United 

 States until 1908. From that time it increased rapidly, 

 especially in the southern states. Numerous efforts have 

 been made to discover the etiology of the disease, which 

 is characterized by stomatitis, diarrhea, dermatitis, and 



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