VITAMINES 1 



By H. W. BYWATERS, D.Sc. (London and Bristol) 



In the days when physiology was just beginning to be recog- 

 nised as a distinct science, the articles of our food were regarded 

 as made up of three classes of materials — fats, carbohydrates, 

 and proteins — and it was thought that if these materials were 

 present in the diet in sufficient quantity, the maintenance of 

 healthy life was ensured. 



With the lapse of time the importance of " quality " as well 

 as " quantity " has gradually dawned upon us, and we now know 

 that food must contain not only proteins, carbohydrates, and 

 fats, but certain definite kinds of these principles, together with 

 small quantities of mineral salts, if it is to be considered 

 satisfactory from the maintenance-of-health point of view. If 

 the protein element, for instance, is deficient in certain amino- 

 acids, especially in aromatic amino-acids, such as tyrosine and 

 tryptophane, no superabundance of other amino-acid con- 

 stituents will compensate for the deficiency, and the food is 

 unable to maintain the integrity of the living tissues. 



The essential factors of a complete diet are therefore more 

 numerous than was formerly suspected, and the recognition of 

 the limitation of the synthetic powers of the living organism has 

 suggested the possibility that other substances ma}' be present 

 in the food — occurring, it may be, in only small quantities — 

 which are nevertheless absolutely indispensable, whose with- 

 drawal from the diet would be attended with eventually fatal 

 results. We know that there are certain mysterious substances 

 in the body — the so-called " internal secretions," hormones, 

 enzymes, and so forth — of which very small traces bring about 

 changes of immense importance to the living organism. These 

 substances are being constantly destroyed and renewed, and the 

 peculiarity of their structure suggests that their elaboration is 

 dependent upon the presence in the food of materials essentially 



1 Based on a Public Lecture given at the University of Bristol on March 

 6, 1914. 



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