826 METABOLISM. 



from the sulphates of the food, makes nearly equal variations with the 

 elimination of nitrogen by the urine. If the amount of nitrogen and sul- 

 phur in the proteins is considered as 16 per cent and 1 per cent respectively, 

 then the proportion between the nitrogen of the proteins and the sulphuric 

 acid, H 2 S0 4 , produced by their combustion is in the ratio 5.2:1, or about 

 the same as in the urine (see page 726) . The determination of the quantity 

 of sulphuric acid eliminated in the urine gives us an important means of 

 controlling the extent of the transformation of proteins, and such a con- 

 trol is especially important in cases in which it is expected to study the 

 action of certain nitrogenous non-albuminous bodies on the metabolism 

 of proteins. A determination of the nitrogen alone is not sufficient in 

 such cases. A perfectly positive measure of the protein catabolism 

 cannot be made from the sulphuric acid of the urine, as the various protein 

 substances have a rather variable sulphur content, and on the other hand 

 also a variable quantity of the sulphur in the urine exists as so-called 

 neutral sulphur. 



In metabolism experiments the total sulphur of the urine as well as the 

 f eces must be determined, and it may also be of importance to determine the 

 relation between the sulphuric acid-sulphur and the neutral sulphur of the 

 urine. The sulphur of the catabolized proteins is more quickly eliminated, 

 according to v. WENDT, HAMALAINEN and HELME l than the nitrogen, and 

 this behavior of sulphur gives a more positive picture of the temporal catab- 

 olism of protein than the nitrogen. This is of importance, as the elim- 

 ination of the nitrogen corresponding to a certain amount of protein 

 requires several days for completion. FALTA has also observed that the 

 chief amount of nitrogen in man on taking different proteins is secreted 

 vith varying rapidity, and the same is true, according to HAMALAINEN 

 and HELME, for the elimination of sulphur, as in their experiments the 

 sulphur elimination from white of egg required about six days and from 

 casein only two days. These conditions must be considered in metab- 

 olism experiments. 



Besides lecithins and other phosphatides the body takes with its food 

 pseudonucleins as well as true nucleins, and these are absorbed more or 

 less completely from the intestinal tract and then assimilated (GuMLicn, 

 SANDMEYER, MARCUSE, ROHMANN, and STEINITZ, LoEwi, 2 and others). 



1 Wendt, Skand. Arch. f. PhysioL, 17; Hamalainen and Helme, ibid., 19; Falta, 

 Deutsch. Arch. f. klin. Med., 86. 



2 In regard to the investigations on the metabolism of phosphorus and the methods 

 used therein, see Steinitz, Pfliiger's Arch., 72; Zadik, ibid., 77; Leipziger, ibid., 78; 

 Oertel, Zeitschr., f. physiol. Chem., 26; Mandel and Oertel, Bull. Med. Sciences, N. Y. 

 Univ., 1, and Ehrlich, Inaug.-Diss., Breslau, 1000; Loewi, Arch, f. exp. Path. u. Pharm., 

 45; Slowtzoff, Hofmeister; Beitrage 8. On the absorption of casein, see Poda, Praus- 

 nitz, Micko, and P. Miiller, Zeitschr. f . Biologic, 39. The literature on the phosphorus 



