250 SCIENCE REMAKING THE WORLD 



instead of what we should." In those days, too, at- 

 tempts to describe a good diet in purely chemical terms 

 were hampered by the embarrassing fact that all efforts 

 to raise animals upon mixtures of carefully purified food 

 substances containing all the chemical compounds then 

 known as essential to foods, had ended in failure; in fact, 

 the purer the chemical substances making up the food 

 mixture, the more certainly did it fail to support normal 

 nutrition. Whether nutritive failure resulted from the 

 need of other substances in addition to those then known 

 as essential, or from faulty selection or combination of 

 the nutrients entering into the artificial food mixture, 

 remained obscure until about ten years ago when the 

 work of Hopkins in England, and of Osborne and Men- 

 del and McCollum and Davis in this country, made it 

 clear that an adequate food supply must furnish cer- 

 tain substances which are absolutely essential but whose 

 existence was previously unknown, and which we now 

 know as the vitamins. 



Although the vitamins have not yet been isolated in 

 pure form, nor their chemical nature determined, yet 

 we now know enough of their occurrence in foods and 

 their functions in nutrition to include them in our 

 study and discussion of food values, and we can now 

 describe adequate food supply in chemical terms with 

 confidence that we are taking account of all essential 

 factors. Such a description requires the use of a small 

 number of terms which a few years ago were regarded as 

 technical but which have now become household words 

 through the war-time discussions of food values and 

 food conservation. An adequate food supply may be 



