770 General and Applied Biology ' 



present principally in certain plants and plant products. Animals and 

 animal products may have certain types in rather large amounts. The 

 chief source of vitamins for animals is plants. DifTerent plant and ani- 

 mal foods vary in the types and quantities of vitamins present, some 

 being rich in certain vitamins and poor in others. Although their spe- 

 cific method of action is unknown, minute amounts of them probably 

 act much like enzymes or catalyzers. 



Fig. 371. — Polyneuritis, a dietary disease of animals due to vitamin Bi de- 

 ficiency. Above is a pigeon with a characteristic symptom, while below is the 

 same pigeon a few hours after administration of vitamin Bi. The disease result- 

 ing from this dietary deficiency in man is called beriberi. (From Plimmer: 

 Vitamins and the Choice of Food, Longmans, Green & Co.) 



The first important experiments in search of vitamins were made by 

 Lunin, in 1888, in Switzerland. He fed mice synthetic foodstuffs iso- 

 lated, or prepared, in the laboratory by chemical methods. This diet 

 contained proteins, fats, carbohydrates, and inorganic salts in the quan- 

 tities which Lunin thought were present in milk. When fed on this 



