NUTRITION AND GROWTH. 65 



day from birth to complete maturity in order to reach its normal size, or 

 the full stature fixed by heredity. In other words, it is assumed that the 

 animal has but one way of reaching its full stature and full development, 

 viz., by developing to its upper limit through its entire growth period. This 

 assumes that the organism is utterly incapable of compensating for any 

 retarded development at any time in its growth period, either by a subse- 

 quently increased rate of growth, or by extending, even in the slightest 

 degree, the growth cycle, much less by growing for a time at least when so 

 sparsely fed that no gain in weight occurs.* 



Rubner has expressed the role of nutrition in growth as follows : 



Kanndie Ernahrung auch keinen Wachstumstrieb sehaffen, so kann sie, 

 wenn ungiinstig und unzweckmassig, doch zu einem Hemtnnis des natur- 

 lichen Wachstums werden. Wachstumsbehinderung ist innerhalb gewisser 

 Grenzen noch keine Ursache einer Existenzgefahrdung, ein Kind, dem die 

 Nahrung normales Wachstum hindert, stirbt deswegen durchaus nicht, es 

 holt spater leicht wieder ein, was es versaumt hat . . . Nur das steht 

 sicher, dass die Behinderung des Wachstumstriebes, wie dies wirklich 

 vorkommt, nicht wahrend der ganzen Wachstumsperiode andauern darf, 

 da sonst allerdings die Grosse des Individuums dauernd Schaden leidet. 

 Verlorene Korpergrosse in der Jugendzeit kann nach Vollendung der 

 Wachstumsperiode nimmermehr abgeglichen werden . . . Eine optimah 

 Ernahrung, wie die W achstumserriahrung sein muss, stellt an die richtige 

 Auswahl der Stoffe ganz andere Anforderungen als eine einfache 

 Erhaltungsdiat.f 



Obviously the energy problem plays an important part in the 

 nutrition of growing animals. For the present we are primarily 

 concerned with the qualitative aspects of the diet rather than the 

 quantitative features of the food-intake. These two factors may at 

 times, stand in intimate relation to each other; improperly consti- 

 tuted food may, for example, modify the amount eaten and therefore 

 the energy available for growth. As was intimated in our first 

 report we have been able to arrest development in rats by feeding 

 mixtures containing a single protein; but inasmuch as the food 

 intake was not measured at that time, it was impossible to say 

 whether the chemical character of the diet or a quantitatively inade- 

 quate food consumption was responsible for the dwarfing. The fact 

 brought out was that in these young animals there could be a main- 

 tenance of weight, precisely as in older rats. 



Waters has appropriately emphasized the necessity of a more 

 exact definition of what is meant by maintenance, in contrast with 

 growth. He writes: 







It has long been assumed that the body of an animal, when supplied 

 with only sufficient nutriment to maintain its weight, remains constant in 

 composition and that no growth or production or change of any sort occurs. 



*H. J. Waters: The capacity of animals to grow under adverse conditions. Proceed- 

 ings Society for the Promotion of Agricultural Science, 1908, xxix, p. 3. 

 fRubner: Archiv fiir Hygiene, 1908, Lxvr, pp. 82-83. 



