494 NUTRITIONAL REQUIREMENTS 



that the economy, in the introduction of heterospecific pro- 

 tein containing the protein "building stones " in different 

 quantitative proportions than those characterizing the pro- 

 tein of the body, must not exert a selective activity between 

 these components, throwing out the amino acids that are in 

 excess and concentrating others. * ' The process of transform- 

 ing heterologous into homologous protein, as Abderhalden 

 depicts it, might well explain why an animal with a supply 

 of barely the minimum of protein of fasting cannot be 

 brought into nitrogen balance. If this idea be followed, it 

 must be theoretically possible to restore the nitrogen balance 

 by limiting as far as possible this necessity for selection in 

 regeneration, and by putting at the disposal of the economy 

 the i building stones ' in the same concentration in which they 

 exist in the homologous protein, none of the aminoacids or 

 peptids either in extra or in deficient proportions. In other 

 words, we should give an animal a protein mixture of its 

 own body, that is, a mixture in which the individual tissue 

 proteins are represented in exactly the same proportions as 

 they show in their breaking down in fasting. ' ' Attempts to 

 follow this idea have been made, by feeding dogs after a 

 period of fasting, in some instances with heterologous pro- 

 teins (gliadin, casein, nutrose), in others with a broth made 

 up of dog muscle, various canine tissues and canine serum. 

 The result showed (as, too, in similar experiments carried 

 out by Hosslin and Lesser) 26 that in a general way it is im- 

 possible to maintain an animal in nitrogen equilibrium by 

 giving it no more than the equivalent of protein lost in fast- 

 ing ; that, however, invariably smaller amounts of homologous 

 protein are required to restore this balance than would be 

 required of heterologous protein. The statements of French 

 authors 27 are in harmony with this view, in that the protein 



28 H. v. Hosslin and Lesser (Halle und Mannheim), Zeitschr. f. physiol. 

 Chem., 73, 345, 1911; cf. also F. Frank and A. Schittenhelm, ibid., 70, 99, 1910; 

 73, 157, 1911. 



x H. Busquet, Jour, de Physiol., 11, 399, 1909; G. Billard (Clermont- 

 Ferrand), C. R. Soc. de Biol., 68, 1103, 1910. 



