MVNUAL OF OATTLE-FEEBING. 103 



of nitrogen found in the excrements is the same as that 

 given in the fodder, it 4io\\s, of conrbe, that neither a gain 

 nor a loss has taken pLice. 



In a subsequent chapter we shall see that all our knowl- 

 edge of the laws of the formation of liebh has been obtained 

 in tliis way, and that consequently the truth of those la^\s 

 dependb on the truth of the view that the urinary nitiogen 

 id a measure of the amount of protein decomposed in the 

 body. 



Excretion of Carbon.^ — The carbon of the organic 

 matters destroyed in the body is excreted in two msljs. 



Fart of it leaves the body in the various urinary prod- 

 ucts, but by far the larger portion is excreted as carbonic 

 acid through lungs and skin, as already described, so that 

 an investigation into the gain or loss of carbon by the ani- 

 mal b<Kiy requires a determination of the gaseous ezereta. 



Exeretion of Hydrogen. — A portion of the hydrogen 

 of tlie tissues is also excreted through the kidneys a little 

 of it in combination with carbon, nitrogen, and oxygen, in 

 the urea, etc., but most of it in the fonn of water. 



Considerable quantities of water are also excreted 

 through the lungs, as is made evident by the visible con- 

 densation of the moisture of the breath on a cold day, and 

 likewise thi^ough the skin. 



