286 JXFLAMMATJOX. RECEy ERATIOy . aROWTH 



not only provide a sufficient amount of nitrogen, but they must also 

 provide certain specific amino-acids, as has been especially demon- 

 strated by the investigations of Osborne and JMendel.'^ Apparentlj' 

 the presence of some of the simj)le straight-chain amino-acids can be 

 dispensed with (c. g., g-lycine), and the animal will grow and thrive 

 if other nutritive supplies are adequate, but certain, at least, of the 

 more complex cyclic amino-acids must be provided. Furthermore, 

 the requirements for growth (quantitatively speaking at least), seem 

 to be sometliing more than the requirements for mere preservation of 

 health and equilibrium, for it was found that animals could live and 

 preserve nitrogen equilibrium when the protein of the diet furnished 

 at most small quantities of lysine, but young animals were unable to 

 grow with such a restricted supply of this amino-acid. If lysine was 

 added to the defective protein (gliadin from wheat) the animal would 

 then be able to grow at a normal rate. Of particular importance is 

 the fact that animals can be kept in a stunted condition on such a 

 deficient diet until they have reached an age at which normally all 

 growth would have long since ceased, and then when supplied with 

 sufficient lysine they will begin to grow and continue until full size is 

 reached.^* This last observation proves that growth is not condi- 

 tioned by age, and that we do not stop growing because a certain age 

 is reached : the capacity for growth may remain latent and capable 

 of exhibiting itself when proper conditions are furnished. But no 

 amount of any amino-acid will cause a fully grown animal to grow 

 any more, so it would seem that the capacity for growth becomes ex- 

 tinguished when it has been utilized to a certain fixed extent, and re- 

 mains potent until it has been completely utilized. 



If the only protein furnished contains no tryptophane the animal 

 cannot maintain itself and slowly loses weight until it dies, unless 

 tryptophane is supplied. If zein from corn, which yields neither h'- 

 sine nor tryptophane, is the sole protein, then the animal cannot grow 

 unless both lysine and tryptophane are added to the diet. That the 

 pure isolated amino-acids can meet the deficiencies when added to the 

 imperfect protein ration, demonstrates that proteins ser^'e for food as 

 amino-acids, and not as larger complexes. 



Not only must the proteins present certain essential chemical com- 

 pounds to the living and growing organism, but also an adequate 

 su])])ly of the essential inorganic salts and certain other less well de- 

 fined substances are also necessary to permit of maintenance, growth 

 and repair. It has long been recognized clinically that certain dis- 

 eases, notably scurvy, may result from tlu> absence of some essential 

 food supply. More recently other diseases have been proved or sus- 

 pected of having a similar cause, and the study of one of these, beri- 



13 Series of papers in Jour. Biol. Clioiii.. 1!)12, ct scf/. 

 ^•».Tnnr. P.inl. Diem., 1915 (23), 4:W. 



