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PRINCIPLES OP VETERINARY SCIENCE 



tioned, other investigators had announced the discovery in 

 foodstuffs of a substance or substances necessary for growth to 

 which they gave the name vitamines. However, they had no 

 conception of the nature of vitamines until McCollum published 

 the results of his work showing that they contain two separate 

 and distinct factors, each of which differs in several ways from 

 the other and both of which are equally important, as is shown 

 by the fact that the absence of either will cause failure of growth. 

 He has termed one the fat soluble A and the other the water soluble 

 B factor. Although nobody has yet determined their chemical 

 properties, it is known that they are not destroyed by moderately 

 high degrees of heat. 



Fig. 32. — Pigs of the same age on a nutrition experiment. The animal on 

 the left (55 pounds) received a ration of 95.5 parts of wheat meal and 2.5 parts 

 of wheat gluten. The animal on the right (165 pounds) received a ration of 

 wheat meal and skim-milk fed in approximately the proportions of 1:1. 

 (Wisconsin Bulletin 291.) 



Later the presence of both the essential fat and water soluble 

 substances was demonstrated in alfalfa, clover, and cabbage 

 leaves. It is probable that the leaves of all forage plants con- 

 tain them. Be this as it may, there is no doubt that all seeds 

 contain a much smaller amount of these substances than do the 

 leaves. Butterf at contains an abundance of the fat soluble A, and 

 skim-milk an abundance of the water soluble B. However, neither 

 class of vitamines is constructed by the cow. The animal 

 concentrates them from the feed and places them in the milk. 

 In other words, the cow's feed must contain them, otherwise she 

 would be unable to secrete normal milk. 



One would expect to find the fat soluble A in all common fats. 



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