48 PRINCIPLES OF ANIMAL NUTRITION. 
NITROGEN IN PERSPIRATION.—The perspiration of such animals 
as secrete this fluid must be regarded as one of the minor channels by 
which nitrogen is excreted. In human perspiration there have been 
found, in addition to small amounts of proteids, urea, uric acid, 
creatinin, and other nitrogenous products of the proteid meta- 
bolism. In a recent investigation, Camerer * found about 34 per 
cent. of the total nitrogen of human perspiration to be in the form 
of urea, about 7.5 per cent. existed as ammonium salts, and the 
remainder in undetermined forms, including uric acid and traces 
of albumen. 
The total quantity of nitrogen excreted in the insensible perspi- 
ration appears to be insignificant. Atwater & Benedict + found 
it to amount to 0.048 gram per day for an adult man in a state 
of rest. Rubner & Heubner { obtained from the clothing of an 
infant 2.83 mgrs. of ammonia and 0.0205 mgr. of urea per day 
and estimated the total nitrogen of the perspiration at 39 mers. 
- When the secretion of sweat is stimulated by work or a high 
external temperature the amount of nitrogen excreted may be con- 
siderably increased as compared with a state of rest, although its 
absolute amount is still small. Atwater & Benedict,§ in a work ex- 
periment, observed an excretion of 0.220 gram of nitrogen per day 
in the perspiration of man. 
The Non-nitrogenous Residue of the Proteids.—The various 
nitrogenous products found in the urine and other excreta, the most 
important of which have been noticed above, are believed to con- 
tain all the nitrogen of the metabolized proteids. This does not 
imply, however, that a quantity of proteids equivalent to this nitro- 
gen, or even to that of the urine, has been completely oxidized to the 
final products of metabolism, viz., carbon dioxide, water, and urea 
and its congeners. 
A comparison of the ultimate composition of the proteids with 
that of the nitrogenous products of their metabolism reveals the 
fact that an amount of the latter sufficient to account for all the 
nitrogen of the proteids contain but a relatively small part of their 
carbon, hydrogen, and oxygen. Taking urea as the chief and 
* Zeit. f. Biol., 41, 271. 
+U. 8S. Dept. Agr., Office of Expt. Stations, Bull. 69, 73. 
{Zeit. f. Biol., 86, 34. 
§ Loe. cit., p. 53. 
