440 PHYSIOLOGICAL CHEMISTRY. 



numerous investigations. The conclusion has been drawn from 

 the researches of REGNAULT and REISET on respiration that also 

 an exhalation of nitrogen takes place. SEEGEN and NOWAK espe- 

 cially have recently endeavored to prove the correctness of this con- 

 clusion. Such an experiment is, however, accompanied with so 

 many difficulties, and there are so many sources of error, that it can 

 scarcely be considered as conclusive. In fact, PETTENKOFER and 

 VOIT have demonstrated the existence of errors in the experiments 

 of SEEGEN and NOWAK. On the other hand, PFLUGER and LEO 

 have found no appreciable exhalation of nitrogen in rabbits. Also 

 many investigators, especially VOIT, PETTENKOFER and VOIT and 

 RANKE, have shown by experiments on man that with the proper 

 amount and quality of food we can bring the body into NITROGE- 

 NOUS EQUILIBRIUM, in which the quantity of nitrogen voided with 

 the urine and faeces is equal to the quantity contained in the food. 



The experiments made by GRUBER in VOIT'S institute seem to 

 be especially conclusive on this point. GRUBER fed a dog seventeen 

 days on meat which in all contained 368.53 grms. nitrogen, and he 

 found in the same time 368.28 grms. nitrogen in the urine and 

 faeces. From this and other experiments we may conclude with 

 VOIT that a deficit of nitrogen does not exist; or if we consider the 

 above-mentioned very small loss of nitrogen through the horny 

 structure, etc., it is so insignificant that in experiments upon the 

 exchange of material it need not be considered. In investigations 

 on the metabolism of proteids in the body, ordinarily, it is only 

 necessary to consider the nitrogen of the urine and faeces, but it 

 must be remarked that the nitrogen of the urine is a measure of the 

 extent of the metabolism of the proteids in the body, while the 

 nitrogen of the faeces (after deducting somewhat less than 1 grm. 

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

 of the food. 



In the oxidation of the proteids 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 

 only to a small extent derived from the sulphates of the food, makes 

 nearly equal variations as the elimination of nitrogen by the urine. 

 If we consider the amount of nitrogen and sulphur in the proteids 

 as 16$ and 1$ respectively, then the proportion between the nitrogen 



