84 MANUAL OF CATTLE-FJEEDIISrG. 



ones the same substances, and in addition Vjrea^ tlie eliar- 

 acteristic ingredient of tlie nrine. Urea is a crystallizable 

 body of comparatively simple composition^ which, together 

 with small amounts of other substances, contains all the 

 nitrogen and part of the carbon and hydrogen of the 

 albuminoids from which it is derived. In the urine of 

 herbivorous animals it is, in part, replaced by MppibTio 

 acid. All these oxidations take place in the cells and 

 capillaries of the body, and it is there, consequently, and 

 not, as is sometimes stated, in the lungs, that the animal 

 heat is produced. 



The quantity of oxygen *whieh passes into the 

 blood is by no means determined by the depth and fre- 

 quency of the inspirations, but by the amount needed in 

 the lody / that is, in the first place, by the rapidity of the 

 decomposition of substances in the blood and tissues, as 

 well as, in the second place, by the number and quality of 

 the blood corpuscles. 



In all parts of the living body a continual decomposi- 

 tion of its materials is going on, and all manifestations of 

 life are intimately related to this metamorphosis of the 

 materials of the living organism. 



This decomposition, as has been already pointed out^ 

 consists, in the main, in a splitting up of complex com- 

 pounds into simpler ones, accompanied by a liberation 

 of energy, which manifests itself in various ways. The 

 processes tafee place according to fixed laws and at first in- 

 dependently of oxygen, but the products of the decomposi- 

 tion unite with the oxygen of the blood and regulate the 

 amount of this substance taken up in respiration. The 

 splitting up of substances in the body to form simpler 

 compounds must be regarded as the primary process and 

 tlie taking up of oxygen as the secondary, although it was 



