336 HUMAN BIOLOGY 



characteristic of scurvy in man. They showed that scurvy 

 would develop in guinea pigs confined to dried or cooked 

 foods and that scurvy was prevented by the inclusion of small 

 additions of fresh green foods such as dandehons. Their 

 experimental work placed upon a scientific footing the knowl- 

 edge of the etiology of scurvy which had been vaguely 

 recognized since the appearance of a book on this disease 

 written by James Lind in 1754. Lind recognized the impor- 

 tance of fresh uncooked vegetable foods in the diet for the 

 prevention or cure of scurvy, and his advice was acted upon 

 for many years in the rationing of soldiers, sailors and 

 prisoners before any clear concept was gained as to the nature 

 of the substance in certain foods which prevented this 

 disease. 



In 1922 it was demonstrated that there is a special vitamin, 

 now designated as d, in cod liver oil which plays a special 

 role in bone growth and is a protective agency in the pre- 

 vention or cure of rickets in infants and animals. In 1922 

 Evans and Bishop discovered the existence of a vitamin 

 which plays a special part in fertihty. It may be explained 

 that a system of nomenclature was adopted in 1916 whereby 

 the class of nutrient principles typified by that discovered 

 by Eijkman in 1897, of which very small amounts in the 

 diet suffice for the promotion of health, are designated by 

 the first letters of the alphabet. They are now known as 

 vitamins a, b, c, d, e and f. Vitamin F, the most recently 

 discovered of these principles, was demonstrated by Smith 

 and Hendrick, and later shown by Goldberger to be con- 

 cerned in the etiology of pellagra, which is now generally 

 beheved to be a vitamin-deficiency disease. 



As our knowledge now stands it is accepted that vitamin a 

 when lacking in the diet causes damage especially to cells of the 

 epithelial type. Glandular structures such as the lacrymal glands, 

 sahvary glands, and digestive glands, suffer injury and partial or 

 total loss of function. As a result of such injury to the lacrymal 

 glands eye secretion is interfered with, and the consequent drying 

 of the eyes together with the bacterial growth which freely takes 

 place in the conjunctival sac results in profound injury and 

 eventually in destruction of the eye. This is so characteristic 

 that observations on the appearance of ophthalmia under a 



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