is deficient in certain of these unknown chemical compounds, 

 the vitamines. Also beri beri may be caused by a diet of 

 bread and macaroni from highly milled wheat flour. How- 

 ever, unpolished rice, or polished rice and rice bran, or 

 whole wheat flour do not produce beri beri, incUcating that 

 the so-called vitamines are present in the outside coats of 

 rice and wheat. 



McCoUum and Davis ^ fed mixtures of casein (a complete 

 protein), carbohydrates, and mineral matter to young rats. 

 Normal growth ensued for 3 to 4 months })ut then ceased. 

 The addition to the ration of butter fat, egg-yolk fat, kidney 

 fat (fat from the kidney itself, not the fat surrounding the 

 kidney), fat from corn, or fat from wheat germ caused 

 normal growth. However, the addition of lard, ohve oil, 

 cottonseed oil, or tallow did not add to the value of the 

 basal ration. Later Osborne and Mendel ^ found that cod 

 liver oil and the Ughter oils of beef fat, added to the basal 

 ration, produce normal growth, but they are not as efficient 

 for this purpose as is butter fat, as larger amounts are re- 

 quired for normal growth. 



Little or nothing is definitely known at this time as to the 

 chemical composition, properties, and occurrence of these 

 substances, or vitamines. However, they apparently play 

 a very important role in nutrition. 



It is difficult to say at the present time whether further 

 knowledge of the vitamines will have any practical value in 

 the feeding of farm animals. It is quite probable that it 

 may, particularly in the case of hogs, where there ordinarily 



» Jour, of Biol. Chem. XV, 1913, p. 167; XIX, 1914, pp. 245 and 373; 

 XX, 1915, p. 641; XXI, 1915, p. 179; XXIII. 1915. pp. ISl and 231. 

 2 Jour, of Biol. Chem. XVII, 1914, p. 401. 



