34 PHYSIOLOGY AND NATIONAL NEEDS 



always ignored. Clearly the ability of proteins, 

 fats, carbohydrates, and inorganic salts by them- 

 selves to support life could only be proved by giving 

 them pure. 



Suppose, now, we feed animals with a mixture 

 containing really pure protein, such as purified 

 casein from milk, purified starch, and pure sugar, 

 together with a vegetable fat (I say vegetable 

 fat for a reason which will shortly be made clear), 

 and the requisite mineral salts — what is the 

 result ? Not normal nutrition by any means ! 

 On such a food young animals fail to grow and 

 all animals, even adults, sooner or later go to 

 ground. 



The full significance of these facts will not be 

 appreciated unless it be recognised that these puri- 

 fied diets are perfectly wholesome : they are fully 

 digested, and may be eaten, so far as quantity is 

 concerned, in amount ample for normal growth and 

 maintenance. Something, however — something 

 clearly of the greatest importance — is lacking. Ex- 

 periments which prove these statements, and the 

 further discriminative experiments to which I shall 

 refer, have hitherto been made almost exclusively 

 upon animals ; for the most part, indeed, upon rats, 

 because of the extreme convenience of these subjects. 

 But for those who feel prejudice against applying 

 results so obtained to the nutrition of Man (an 

 unjustifiable prejudice, let me say), I shall later 



