882 METABOLISM. 



in the body, while the nitrogen of the feces (after deducting about 1 gram 

 on a mixed diet) is a measure of the non-absorbed part of the nitrogen of 

 the food. The nitrogen of the food, as well as of the excreta, is generally 

 determined by KJELDAHL'S method. 



In the oxidation of the proteins in the organism, their sulphur is oxidized 

 into sulphuric acid, and on this depends the fact that the elimination of 

 sulphuric acid by the urine, which in man is but to a small extent derived 

 from the sulphates of the food, nearly makes 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, H2SO4, produced by their combustion is in the ratio 5.2 : 1, or about 

 the same as in the urine (see page 765). 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, or to decide the question whether a true protein combustion 

 and not only a washing out of the nitrogenous products of metabolism 

 from the tissues is taking place. A determination of the nitrogen alone 

 is naturally 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 

 feces 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 elimination of the sulphur originating from the proteins 

 does not, according to v. WENDT, HAMALAINEN and HELME and CH. 

 WOLFF l always run parallel with the protein nitrogen, and for the 

 white of egg the maxima of the elimination curves may indeed be 

 separated during a period of twenty-four hours (WOLFF). The sulphur 

 is more quickly eliminated than the nitrogen, and this behavior of sul- 

 phur gives in certain cases a more positive picture of the temporal 

 catabolism of protein than the nitrogen. This is of importance, as the 

 elimination 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 

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



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

 Deutsch. Arch. f. klin. Med., 86; Ch. G. Wolff, Bioch. Zeitschr., 40. 



