24 THE VITAMINES 



showed inhibition of growth, while full grown animals suffered from 

 paresis and sterility. This last symptom was not to be attributed 

 to lack of tryptophane. The animals whose growth had been stunted 

 resumed normal growth on a mixed diet. 



About 1906, there appeared the classical work of Hopkins and his 

 pupils, who displayed marked clearness in their course of reasoning. 

 Hopkins fed mice on a mixture which contained zein (one of the corn 

 proteins) which lacks tryptophane. The young animals were able to 

 live only 16 days, whereas upon the addition of this amino acid, life 

 was prolonged for 14 days more. Tyrosine exerted no influence. It 

 appeared from these results that the above diet was lacking in some- 

 thing else besides tryptophane. The appearance of animals so fed, 

 as described by Wilcock and Hopkins (22) was not very bright. The 

 animals were torpid, had cold extremities, half-closed eyes and slimy 

 fur. At that time, Hopkins thought that tryptophane could be 

 conceived of as the precursor of adrenaline. The chemical nature of 

 the missing components (even after the addition of tryptophane) was 

 not recognized at that time, although the experiments led Hopkins (23) 

 to the prophetic statement which is reproduced here verbatim: 



But further, no animal can live upon a mixture of pure protein, fat and 

 carbohydrate, and even when the necessary inorganic material is carefully 

 supplied, the animal still cannot flourish. The animal body is adjusted to 

 live either upon plant tissue or other animals and these contain countless 

 substances other than the proteins, carbohydrates and fats. Physiological 

 evolution, I believe, has made some of these well nigh as essential as are the 

 basal constituents of diet; lecithin for instance, has been repeatedly shown 

 to have a marked influence upon nutrition, and this just happens to be some- 

 thing familiar, and a substance that happens to have been tried. The field 

 is almost unexplored, only it is certain that there are many minor factors in 

 all diets of which the body takes account. In diseases, such as rickets, and 

 particularly scurvy, we have had for long years knowledge of the dietetic 

 factor, but though we know how to benefit these conditions empirically, the 

 real errors in the diet are to this day quite obscure. They are, however, 

 certainly of the kind which comprises these minimal quantitative factors 

 that I am considering. Scurvy and rickets are conditions so severe that they 

 force themselves upon our attention, but many other nutritive errors affect 

 the health of individuals to a degree most important to themselves, and some 

 of them depend upon unsuspected dietetic factors. 



All that Hopkins says in this short paragraph applies to this very 

 day, although from the point of view of that time it was held, for 

 example, that lecithin was essential for life. These assertions of 



