METABOLISM 223 



deficiencies in the diet, and the term "vitamin," now often 

 spelled without the final "e," has become a household word. It 

 is possible very briefly to summarize the enormous amount of 

 work which has been done in this field in the last ten years. 



At present nothing is known of the chemical constitution of 

 the vitamins. At least four are believed to exist, and since they 

 are of unknown structure they have been given the provisional 

 designations A, B, C, and D. Absence of any one of these sub- 

 stances from the diet will cause serious disorders even to the 

 point of .death. In the case of an animal suffering from a lack 

 of one of the vitamins, remarkable recovery may be brought 

 about by feeding extremely small amounts of the missing sub- 

 stance, either in the form of an extract or a food containing 

 the vitamin. The following brief summary gives the essential 

 facts which are known at present. 



Vitamin A. A shortage of A results in failure to grow in 

 young animals, and in a disease of the eyes, xerophthalmia, in 

 which the eyes are very subject to infection, and which may 

 result in blindness. A is found in butterfat and milk, in which 

 it is present in particularly large amounts if the cow has been 

 fed on green fodder, in smaller amounts if the animal has been 

 stable fed. It is found in egg yolk, the germ of cereals, and 

 green leaves for example cabbage and lettuce, and also in large 

 amounts in cod liver oil. It may be stored in the body to some 

 extent. It is soluble in fats, ether, alcohol-ether and some other 

 solvents. It is fairly stable to heat, quite so in acid and less so 

 in alkaline solution. It is stable to drying, but is destroyed by 

 hydrogenation. By reason of its distribution and stability it 

 is not likely to be lacking in the diet, but dairy products and 

 green leaves should be included to secure an adequate supply. 



Vitamin B. A shortage of B results in failure to grow, in 

 the young, and in adults leads to the disease known as beri-beri, 

 mentioned above. More recent work has shown that B has a 

 marked effect in stimulating the appetite, and much evidence 

 points to the conclusion that it has some connection with the sex 

 interests and functions. Rats on a diet deficient in B become 



