66 FEEDING EXPERIMENTS WITH ISOLATED EOOD-SUBSTANCES. 



It is true that the term maintenance has been used somewhat loosely, but 

 in general we have been in the habit of regarding the animal in maintenance 

 when its live weight was constant. A more correct definition of the term 

 would perhaps be to say that the animal was in maintenance when its body 

 was in energy balance, but the live weight has been the conventional 

 measure of our maintenance values.* 



It is generally admitted that the proteins satisfy several functions 

 in a growing organism as well as in the adult. The first is that of 

 maintenance, corresponding with what has been termed the " Abnut- 

 zungsquote, " or wear-and-tear, by Rubner. This makes good the 

 inevitable losses occasioned by the processes of metabolism, cellular 

 and secretory processes, etc. It is a small yet ever present need 

 for protein (as well as energy), representing in a general way the 

 minimal protein need of the stationary organism. Any excess of 

 protein beyond this maintenance requirement may, in the adult, 

 experience temporary storage (" Ansatz") or be devoted to dynamo- 

 genie purposes ; but in the organism capable of development it con- 

 tributes a share toward growth. It should be emphasized that the 

 rate of growth is not by any means proportional to the excess of 

 protein available. It is surprising, indeed, how small a content of 

 protein in the dietary suffices to make growth possible. Rubner and 

 Heubnerf found, for example, that in suckling infants a protein 

 intake equivalent to 5 per cent of the total calories satisfies the protein 

 needs of maintenance, while 7 per cent permits of growth. Rubner 

 writes: 



Das Wachstum ist erne Funktion der Zelle, es kann durch unzureich- 

 ender Eiweisszufuhr latent werden, aber Eiweiss vermag nicht die Wach- 

 stumsschnelligkeit iiber die von der Natur gestreckten Grenzen zu heben, 

 daher wird mit steigender Eiweissmenge in der Kost prozentisch weniger 

 verwertet und das tiberflussig zugefiihrte Eiweiss wird einfach als Brennstoff 

 verbraucht der isodyname Mengen N-freier Stoffe einspart. Diese starke 

 Anziehung von Eiweiss zum Wachstum nimmt im Laufe der Entwickhmg 

 ab und ist am grossten in der ersten Zeit des Lebens.^ 



Waters has found in his extensive studies on cattle that growth, 

 in the sense of changes of size and form, may occur even under 

 adverse nutritive conditions. Fundamentally such investigations 

 touch upon the much controverted question as to the relative impor- 

 tance of breeding and feeding in determining the shape and activities 

 of mature animals. It is well known that by limiting the food supply 

 of an ungrown individual, its development may be retarded. If the 

 underfeeding is prolonged through the cycle of growth, the full 

 stature limited by heredity may not be reached. 



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

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



fRubner and Heubner: Zeitschrift fiir experimentelle Pathologie, 1905, I, p. 1. 

 JRubner: Archiv fiir Hygiene, 1908, i,xvr, p. no. 



