110 GENERAL ZOOLOGY 



pure state, so that their chemical formulas are not known with 

 any degree of certainty, at least in all cases. Their importance 

 as essential constituents of a diet has been established beyond 

 all question. They occur in milk, fruit, fresh vegetables, meat, 

 and in the outer kernels of grain. Vitamins exist in such small 

 quantities in foods that they are negligible as sources of energy. 

 They are not enzymes. Their precise role is unknown, but there 

 is some resemblance between them and hormones. Some authors 

 designate them as exhormones to indicate their origin outside the 

 body in contrast to the hormones of the endocrine glands which 

 are formed within the body. 



At the present time, five vitamins, known as A, B, C, D, and 

 E, are recognized, with some evidence to indicate that vitamin 

 B is a combination of two or more vitamins. 



Vitamin A is fat-soluble and promotes growth. Rats on a 

 vitamin A-deficient diet show in addition to stoppage of growth 

 and loss of weight, inflammatory conditions in the conjunctiva 

 and the cornea of the eye, as well as other effects. Cooking does 

 not destroy it in fruits and vegetables. 



Vitamin B or B i is water-soluble and its absence in food pro- 

 duces polyneuritis or beriberi. Fowls fed on polished rice (rice in 

 which the reddish outside layer has been removed) develop in the 

 course of a few days a weakness in the legs caused by a nervous 

 degeneration which is known as polyneuritis. Such fowls soon 

 die unless the diet is changed, or rice polishings added to it. 

 Beriberi, a disease common among rice-eating peoples, shows 

 similar symptoms and seems to be due to similar causes. In 

 this case the vitamin involved is located in the cortex of the grain. 

 It also occurs in yeast, milk, leafy vegetables, and fruit. 



Vitamin C is alcohol-soluble and is antiscorbutic. Absence of 

 vitamin C in the diet produces scurvy, a disease manifested by 

 bleeding of the gums, tooth pulp, mucous membrane, and skin. 

 It was particularly prevalent among sailors in the days of sailing 

 vessels when voyages too frequently outlasted the available 

 supply of fresh vegetables and meat. Scurvy results in bodily 

 weakness and terminates in death unless checked by feeding 

 vegetables and meat or by giving the juice of lemons, limes or 

 oranges. Ascorbic acid, C 6 H 8 6 , has the antiscorbutic potency 

 of lemon juice, of which it is one of the constituents. 



Vitamin D is fat-soluble and antirachitic. Rickets, a disease 

 in which the bones and teeth are defective, may be prevented by 



