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PRINCIPLES OF ANIMAL BIOLOGY 



These essential substances were given the collective name of vitamins 

 before anything was known of their identity. These substances, in 

 small quantities, are needed for healthy activity or growth. If any of 

 them is lacking, or present in too small amount, a deficiency disease results. 

 The disease is specific for each of the vitamins. 



The earliest known and recognized of the deficiency diseases was 

 scurvy. Before the end of the sixteenth century an officer of the English 



Fig. 92. — The need of vitamin A. Upper two dogs show xerophthahuia caused by 

 deficiency of vitamin A. Lower figure, one of same dogs after 10-day treatment with cod- 

 liver oil. {From Steenbock, Nelson, and Hart in American Journal of Physioloyy.) 



navy observed the bruised skin, bleeding gums, and general anemia of 

 his crew after they had been many months at sea and fresh foods had 

 been exhausted, and he discovered that these symptoms could be com- 

 pletely prevented l)y giving his men a small amount of lime juice daily. 

 The essential feature^ of the lime juice was long designated vitamin C, 

 though its nature was unknown. In 1933 this vitamin was separated 

 out in pure form, and was found to be ascorbic acid, of the chemical 

 formula CeHgOe. It is abundant in citrus fruits (oranges, lemons, limes, 

 grapefruit), many other fruits, tomatoes, and many vegetables. Diets 



