880 METABOLISM. 



the intestine and therefore cannot be quantitatively determined separately. The 

 uncertainty which, because of the intimated difficulties, attaches itself to the 

 results of the experiment, is very small as compared to the variation which is caused 

 by different individualities, different modes of living, different foods, etc. Only 

 approximate values can therefore be given for the constant excreta of the human 

 body. 



The following figures represent the quantity of excreta for twenty- 

 lour hours from a grown man, weighing 60-70 kilos, on a mixed diet. 

 The figures are compiled from the results of different investigators: 



Grams. 



< Water 2500-3500 



Salts (with the urine) 20-30 



Carbon dioxide 750-&00 



Urea. . 20^40 



Other nitrogenous urinary constituents 2-5 



Solids in the excrement 20-50 



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 different external circum- 

 stances: By respiration about 32 per cent, by the evaporation from the 

 skin 17 per cent, with the urine 46-47 per cent, and with the excrement 

 5-9 per cent. The elimination by the skin and lungs, which is sometimes 

 differentiated by the name " perspiratio insensiblis " from the visible 

 elimination by the kidneys and intestine, is on an average about 50 per 

 cent of the total elimination. This proportion, quoted only relatively, 

 is subject to considerable variation, because of the great difference in 

 the loss of water through the skin and kidneys under varying circum- 

 stances. 



The nitrogenous constituents of the excretions consist chiefly of urea, 

 or uric acid in certain animals, and the other nitrogenous urinary con- 

 stituents. A disproportionately large part of the nitrogen leaves the body 

 with the urine, and, as the nitrogenous constituents of this excretion are 

 final products of the metabolism of proteins in the organism, the quantity 

 of proteins catabolized in the body may be easily calculated by multiply- 

 ing the quantity of nitrogen in the urine by the coefficient 6.25 (YB a = 6.25), 

 if it is admitted that the proteins contain in round numbers 16 per cent 

 of nitrogen. 



Still another question is whether the nitrogen leaves the body only 

 with the urine or by other channels. The latter is habitually the case. 

 The discharges from the intestine always contain some nitrogen, which 

 consists in part of non-absorbed remnants of the food, but in chief part 

 and sometimes entirely of constituents of the epithelium and the secre- 

 tions. Under these circumstances it is apparent that one cannot give 

 any exact figures which are valid for all cases for that part of the nitrogen 

 of the excrement which originates in the digestive tract and in the digestive 



