THE GASEOUS EXCRETION. 387 



drawn because the carbohydrates contain enough oxygen to 

 burn their own hydrogen, and the protein nitrogen appears 

 as urea and calls for no outside oxygen. The burning of fat 

 hydrogen is excluded in the assumption. 



The nitrogen of the feces corresponds to 22.5 gin. of orig- 

 inal protein (6.25 X 3-6). Not all of this nitrogen is actu- 

 ally in the form of unchanged or residue protein ; a part of it 

 represents products of metabolism which are excreted in the 

 feces, as explained in a previous chapter. Probably a consid- 

 erable fraction may be considered in that form; but it must 

 be counted as a loss to the body, and we have therefore as net 

 available protein (actually used) about 127.5 8 111 - ^ n tne 

 final metabolism of this the nitrogen appears in urine in sev- 

 eral forms, but mostly as urea. The per cent of nitrogen in 

 this is 46.7. In some of the other compounds the nitrogen 

 is higher and in some lower. In ammonia much hydrogen 

 (relatively) is held, and in uric acid little. In some cases 

 there is an excess of carbon and in other cases relatively little 

 carbon is held with the same weight of nitrogen. The various 

 conditions balance each other pretty well, so that no great 

 error will be made if, for our special purpose, we count all the 

 excreted nitrogen as combined in the form of urea. We have 

 then these relations : 



To oxidize this remaining carbon requires 159.8 gm. of oxy- 

 gen. The 18.3 gm. of protein oxygen will oxidize about 2.3 

 gm. of hydrogen. The remaining hydrogen from the 6 gm. 

 will call for about 29.6 gm. of oxygen, \vhich corresponds 

 closely to the amount calculated above. 



The ingested carbon is seen from the table to be 359 gm. ; 

 the excreted carbon is 279 gm., from which it follows that the 

 body has gained 80 gm. If we assume this to be in the form 



