824 METABOLISM. 



The following figures represent the quantity of excreta for twenty - 

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

 The numbers are compiled from the results of different investigators : 



Grams. 



Water 2500-3500 



Salts (with the urine). . 20-30 



Carbon dioxide 750-900 



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 (^ = 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 as 

 stated in Chapter IX consists in pare of non-absorbed remnants of the 

 food, but in chief part and sometimes entirely of constituents of the epi- 

 thelium and the secretions. 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 fluids. It may not only vary in different 

 individuals, but also in the same individual after more or less active 

 secretion and absorption. In the attempts made to determine this part 

 of the nitrogen of the excrement it has been found that in man, on non- 

 nitrogenous or nearly nitrogen-free food, it amounts in round numbers 



