438 PHYSIOLOGICAL CHEMISTRY. 



These total excreta are approximately divided among the various 

 excretions in the following way but still it must not be forgotten 

 that this division may vary to a great extent under various external 

 circumstances: by RESPIRATION about 32$, by the EVAPORATION 

 FROM THE SKIN 17$, with the URINE 46-47$, and with the EXCRE- 

 MENTS 5-9$. The elimination by the skin and lungs, which is 

 sometimes differentiated by the name " PERSPIRATIO INSENSIBILIS" 

 from the visible elimination by the kidneys and intestine, is on an 

 average about 50$ of the total elimination. This proportion, only 

 quoted relatively, is subject to considerable variation, because of the 

 great difference, in the loss of water through the skin and kidneys 

 under different circumstances. 



About 90$ of the water in carnivora is excreted through the 

 kidneys. In herbivora the excrements, which are 30-50$ of the 

 total excreta, may indeed eliminate 60$ of the water. In man only 

 a smaller fraction of the water (about 5$) is eliminated with the 

 faeces, and the great mass of the water is divided between the kid- 

 neys, lungs, and skin. 



The riitrogenized constituents of the excretions consist chiefly 

 of urea, or uric acid in certain animals, and the other nitrogenized 

 urinary constituents. A disproportionally large part of the nitrogen 

 leaves the body with the urine; and as the nitrogenized constitu- 

 ents of this excretion are final products of the transformation or 

 metabolism of proteids in the organism, the quantity of proteids 

 transformed in the body may be easily calculated by multiply- 

 ing the quantity of nitrogen in the urine by the coefficient 

 6.25 (Vr 6.25), if we admit that the proteids contain in round 

 numbers 16$ nitrogen. 



Still another question is whether the. nitrogen leaves the body 

 only with the urine or by other channels. This last is habitually 

 the case. The discharges from the intestine always contain some 

 nitrogen which has a twofold origin. A part of this nitrogen de- 

 pends upon undigested or non-absorbed remnants of food, and an- 

 other part on the non-absorbed remains of digestive secretions 

 bile, pancreatic juice, intestinal mucus and of epithelium-cells of 

 the mucous membrane. It follows that a part of the nitrogen of 

 faeces has this last-mentioned origin from the fact that discharges 

 from the intestine occurs also in complete inanition. 



