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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-
iour 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 750-900
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 " perspiralio 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 cniefly 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 (
:L
1
Q
6
(l = 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
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