282 SCIENCE REMAKING THE WORLD 



matter is purely a question of nomenclature and we 

 have at least satisfactory evidence to-day of five sub- 

 stances which were hitherto unrecognized in dietary 

 demands and which we consider entitled to names. 

 The list is probably still far from complete. Very re- 

 cently Evans and Bishop have shown that when rats 

 are fed on diets adequate in every known way and in- 

 cluding vitamins A, B, and C, they are often infertile. 

 The addition of lettuce to the diet prevents this sterility. 

 While the distribution of this fertility factor is still to be 

 worked out it is certain that they are dealing with a 

 hitherto unrecognized factor, perhaps the sixth vitamin. 

 These new substances so far as present knowledge is 

 concerned are all alike in being potent in very small 

 amounts and in defying chemical separation or identi- 

 fication except by physiological effects. It may well be 

 that when isolated in free form they will show similar 

 structure, but at present we have no data on which to 

 base even a reasonable guess in this direction. 



The review preceding is essential to make clear ex- 

 actly the relation of the vitamin discovery to proper 

 food evaluation. Enough experimentation has been 

 carried out to date to show that these factors are wide- 

 spread in nature. The following table from the 

 author's Vitamin Manual will give a little idea of thii 

 widespread distribution: 



