498 NUTRITIONAL REQUIREMENTS 



milk-free mixture remained stationary in their develop- 

 ment. 36 



Velocity of Protein Catabolism in Metabolism. Another 

 problem of metabolism which has received much attention 

 is that involving the rapidity of protein break- down in 

 metabolism. A very large number of studies 37 may be inter- 

 preted somewhat as follows : The velocity of decomposition 

 of ingested proteins depends upon the state of nutrition and 

 is the more marked the longer a preceding period of hunger 

 has existed. Postcoenal urea elimination in normal human 

 beings shows a maximum reached in from the fourth to the 

 fifth hour ; 38 if, however, the nitrogen-bearing nutrient mat- 

 ter is given in the form of protein in advanced cleavage the 

 maximum urea-elimination appears earlier (in the course of 

 the first hour) . Elimination of nitrogen and that of sulphur 

 often, but not invariably, proceed in parallel lines ; in many 

 instances the sulphur fraction appears to be the first to be 

 attacked in the cleavage of the protein molecule, and the 

 elimination of sulphur, as a sulphate, precedes the formation 

 of urea. 39 The output of ammonia takes place with greater 

 velocity and at times reaches its maximum in advance of the 

 nitrogen and sulphur. 40 When the protein cleavage occurs 

 with formation of sugar (as in phloridzin diabetes) glucose 

 is excreted before the nitrogen. 41 The carbon coming from 

 the protein is eliminated by the lungs (according to Frank 



88 F. Gowland Hopkins (Physiol. Lab., Cambridge), Jour, of Physiol., 44, 

 425, 1912. 



87 C. Voit, C. Ludwig, Paimm, Falck, Feder, Sonden and Tigerstedt, Lander- 

 gren, Reilly, Nolan and Lusk, Sherman and Hawk, Slosse, Frank and Tromms- 

 dorf, Vogt, Falta, Gigon and Pari, Marriott and Wolf, Camerer, Asher and 

 Haas, Levene, Stauber, Wolf and Osterberg, and others. Cf. Literature: 

 R. Tigerstedt, Nagel's Handb. d. Physiol., 1, 392, 412-1905; A Stauber (E. 

 Freund's Lab., Vienna), Biochem. Zeitschr., 25, 187, 1910; C. G. L. Wolf 



(Cornell Univ., New York), ibid., 40, 194, 1912; 41, 111, 1912. 



88 According to Asher and Haas and to A. Stauber. 



39 Cf. J. Hamalainen and W. Helme ( Helsingfors ) , Skandin. Arch. f. 

 Physiol., 19, 182, 1907. 



40 C. G. L. Wolff, 1. c. 



41 Lusk and his collaborators. 



