94 MANUAL OF CATTLE-FHEDING. 



also a nitrogenous substance. Tlie urine likewise contains 

 traces of various other bodies, nitrogenous and non-niti o- 

 genous, which, on accoimt of their small quantity, are of no 

 special importance here. 



Excretion of Nitrogen. — In the nitrogenous substan- 

 ces of the urine is contained all the nitrogen of the albu- 

 minoids decomposed in the body. This is a most impor- 

 tant fact, and one upon which a large part of the theory 

 of feeding depends, and consequently it is desirable to 

 examine somewhat in detail the evidence upon which it 

 rests, particularly since its truth is still disputed by some 

 authors. , 



The question is, whether the " sensible " excretions, that 

 is, urine and dung, contain all the nitrogen which leaves 

 the body, or whether any considerable portion of it is ex- 

 creted in gaseous form from lungs and skin. 



Since, unfortunately, we have no accurate means of de- 

 termining directly whether free gaseous nitrogen is thus 

 exhaled, we are obliged to approach the subject in an in- 

 direct way, and to determine whether, when no gain of 

 flesh is made by the animal, all the nitrogen of the food 

 reappears in the excreta. 



The earlier experiments on this subject showed, almost 

 without exception, a deficit of nitrogen in the excrements, 

 seldom an excess. Boussingault found, with a horse, a de- 

 ficit of 24: per cent, of the nitrogen of the food ; with a 

 milk-cow, 13 per cent. ; with hogs, 37 and 56 per cent. ; 

 and with a turtle-dove, 34 and 36 per cent. Other ob- 

 servers also obtained a similar deficit, though quite vari- 

 able in amount. 



The extensive respiration experiments of Regnault and 

 Keiset sometimes showed a slight excretion of gaseous 

 nitrogen and sometimes a slight absorption of that sub- 



