BIOLOGY IN HUMAN AFFAIRS 



deficiency the earliest symptoms are deficiency of tears, 

 dryness of the eyes, and dryness of the mouth. The skin 

 becomes dry and scaly, the germinal epithelium in the 

 testes degenerates, and the animals become sterile. 



Attention has repeatedly been called to the occurrence of 

 large numbers of calculi in the kidneys and bladders of rats 

 suffering from deficiency of vitamin A. Rats develop de- 

 posits of phosphates and oxalates in the urinary tract very 

 rapidly, and almost invariably when fed diets deficient in 

 this vitamin. When chickens are fed an A-deficient diet, 

 there accumulate in the kidneys great numbers of crystals 

 of urates, or salts of uric acid, so that the kidneys feel sandy 

 between the fingers. There is also some evidence that gall 

 stones are more likely to develop under conditions of 

 vitamin A insufficiency than otherwise. Plaques of epi- 

 thelial cells desquamate and form nuclei upon which 

 cholesterol deposits. 



One of the earliest observed effects of vitamin A deficiency 

 was the appearance of an ophthalmia characterized by 

 drying of the cornea followed by ulceration and perforation 

 of the eyeball. This has been shown to be a secondary 

 result of injury to the tear glands. The gland atrophies and 

 loses its power to secrete tears; the eyeball thereupon 

 becomes dry, and cornification of the cornea soon develops. 



A number of papers have been published which refer to 

 the incidence of a similar ophthalmia in human subjects 

 subsisting upon diets of poor quality. There is much reason 

 to believe that the occurrence of night blindness is some- 

 times attributable to chronic deficiency of vitamin A. 

 In the intestinal tract there may be impaired absorption 

 due to injury to the epithelial cells of the wall. 



In rats, when the diet is impoverished in vitamin A, the 

 vaginal mucosa forms cornified epithelial cells contin- 

 uously. Under normal nutrition there is a similar cornifica- 

 tion limited to a brief period during which there is growth, 



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