1882.] 



On the Excretion of Nitrogen by the Skin. 



355 



others who have analysed portions of the sweat collected by different 

 methods have found nitrogen, though Schottin and Ranke failed to do 

 so. Funke, by his experiments upon himself and his two pupils, 

 published in 1858, not only found nitrogen in the sweat, but also 

 proved its existence as urea, and was the first to make an estimation 

 of the quantity excreted by the skin of the entire body in a given 

 time. Adopting Schottin's method, he collected, by means of a 

 caoutchouc sleeve, the sweat excreted by the arm in a given time ; and, 

 having filtered, he estimated the quantity of nitrogen present by the 

 combustion process. Then, having established by measurement a 

 ratio between the superficies of the arm and that of the entire body, 

 he calculated the entire cutaneous excretion. Dr. Fleming,* adopt- 

 ing the same method, arrived at almost identical results. I may 

 add that Dr. Fleming's experiments were made subsequently to mine. 



In addition to the unsatisfactory character of all indirect proofs, the 

 investigations of Yoit, Ranke,f Parkes, and others seem liable to a 

 further objection, arising from the extreme difficulty of ascertaining 

 the exact quantity of nitrogen ingested. Again, as already noted by 

 Parkes, the amount of nitrogen excreted, due to waste of animal 

 tissue during the experiment, cannot be determined. These objec- 

 tions seemed to me to make such negative results of doubtful value 

 upon this point; and Professor Parkes' conclusion that, " apart from 

 detached skin structures the balance of evidence is against the passage 

 of nitrogenous substances by the human skin," to my mind, at least, 

 required confirmation. As regards the direct evidence of nitrogen in 

 the sweat the researches of Funke, confirmatory of those of Anselmius, 

 Berzelius, Favre, and others seemed to me to be conclusive on the point. 



Funke's method is the only one by means of which an estimation of 

 the entire cutaneous excretion in a given time has been made, and it 

 alone required re- examination. Funke's method seemed to me to be 

 open to the following amongst other objections : first, the uncertainty 

 attaching to the relative measurement of the superficies of the arm 

 and that of the entire body ; secondly, that arising from the two 

 underlying assumptions — (a) assumed equality of secretive power of 

 rest of body to that of arm, (&) assumed identity of chemical compo- 

 sition of sweat from the arm with that excreted from the rest of 

 body. Considering these grave objections to Funke's method, and the 

 general uncertainty as to any nitrogen being excreted by the skin, I 

 determined, if possible, to ascertain the quantity of nitrogen excreted 

 by the entire skin in a given time without reference to measurement 

 or actual amount of fluid sweat excreted. 



* " Journ. Anat. and Physiol.," vol. xiii, p. 454. 



f Kanke, as above alluded to, endeavoured to obtain nitrogen directly by analysis 

 of the sweat, and failed to do so, but seems to have mainly relied on the indirect 

 argument. 



2 c 2 



