ON THE METHOD OF METABOLISM EXPERIMENTS 89 



from the combined weight of the animal at the end and the total excreta for the 

 period. ED.] 



3. The Apparatus of Sonden and Tigerstedt (Fig. 42). The subject is 

 housed in an ordinary room with a capacity of 100.6 cu.m. The walls, ceiling, 

 and floors are covered with sheet zinc and are made air-tight by soldering all the 

 joints. By means of a hydraulic pump (E) air is drawn from this respiration 

 chamber to a gas meter, where it is measured. Fresh air from outdoors replaces 

 the foul air drawn out. A uniform diffusion of the air in the room is insured 

 by a ventilating fan. 



To obtain air for analysis, a narrow tube branches off from the main inlet 

 pipe (red), and by means of another hydraulic pump a constant stream is main- 

 tained through it, so that the air in the branch always has the same composi- 

 tion as that in the main inlet. At stated intervals samples for analysis are then 

 taken (in the vessel A) from this branch and the carbon dioxide is estimated 

 by the method of Pettersson (B) for the analysis of gases. The quantity of 

 carbon dioxide is calculated by the ventilation formula of Lenz. 



But the body suffers other losses in organic substance than those resulting 

 from combustion. Here belong the losses by sloughing off of the epidermis, 

 cutting the hair and nails, ejection of sperm and menstrual blood, secretion 

 of milk, etc. Such losses, however, are either so slight that they do not affect 

 the results of the investigation, or they come in only occasionally and can 

 generally be neglected, unless the investigation is being directed especially 

 to them. 



C. APPORTIONMENT OF THE INDIVIDUAL ELEMENTS TO THE 

 DIFFERENT EXCRETA 



(1) Expired Air. It has been known since the beginning of scientific 

 investigation of metabolism and can be demonstrated without the least diffi- 

 culty that carbon and hydrogen leave the body as C0 2 and H 2 in the expired 

 air. Not so with the nitrogen and nitrogenous compounds. A priori one 

 cannot deny that such substances also might be given off from the body as 

 products of metabolism in the expired air. But from the many researches 

 which have been carried out with reference to this question, it appears certain 

 that this is not the case. So far as metabolism is concerned we need, there- 

 fore, to consider among the respiratory products only carbon dioxide and 

 water vapor. 



(2) Sweat. Water is the principal substance given off through the skin. 

 However, the sweat contains also some solid substances, the most important 

 of which is urea. With copious sweating, as under severe labor or in a vapor 

 bath, the quantity of these constituents may rise so much that to neglect them 

 would involve considerable error. Thus, under such circumstances, 0.76 g. N 

 have been found in the sweat; at the same time the nitrogen excretion in the 

 urine was 15.9 g. for twenty-four hours. In this case, therefore, the sweat 

 contained 4.8 per cent of the N" eliminated through the kidneys (Argutinsky). 



(3) Urine. Of the chemical elements derived from the organic food- 

 stuffs and found in the urine, nitrogen and carbon are to be specially con- 

 sidered. Both of these occur mainly in the form of urea and uric acid. The 

 daily quantity of nitrogen eliminated in the urine of an adult man amounts 



