NUTRITION AND GROWTH 



609 



The Relationship of Proteins to Growth and Maintenance of Life. 



Since protein constitutes the fundamental chemical basis of the cell, it 

 is natural to devote attention in the first place to this food principle. 

 In the pioneer investigations, studies on the nitrogen balance in young 

 animals yielded results from which it was concluded that the conditions 

 for the disintegration of protein are less developed in young animals 

 than in adults, so that the growing organs rapidly withdraw circulating 

 protein and build it into tissue protein. 



In consideration of the accumulation of data extending over several 

 decades, Rubner denied these conclusions, and showed that the diet of 

 the growing infant is by no means relatively rich in protein. He con- 

 cluded that "growth is not proportional to the quantity of protein in the 

 diet." Important though this pioneer work may have been in the de- 

 velopment of our present-day conception, the viewpoint of the men who 

 carried it out was very much narrowed on account of the paucity of 

 knowledge concerning the structure of the protein molecule. No allow- 

 ance was made for the fact, which has recently been firmly established, 

 that the protein molecule may vary extremely in regard to the units 

 of which it is composed, and that the growing tissues may demand, not 

 so much an abundance of protein as such, but rather a proper supply of 

 all the .building stones which are required for growth (Mendel). 



QUANTITATIVE COMPARISON OF AMINO ACIDS OBTAINED BY HYDROLYSIS OF PROTEINS* 

 (Compiled by T. B. Osborne, 1914) t 



*These analyses are combinations of what appear to be the best determinations of various 

 chemists. 



fThe figures for the more recent analyses of gliadin are inserted. 



From the accompanying table giving the percentage of the various 

 amino acids, etc., present in certain proteins, it will be evident that there 



