URINARY ORGANS. 73 



"The distribution of oxygen through the body is ac- 

 complished by means of the circulation. Each little cor- 

 puscle carries its load of oxygen from the lungs through 

 the heart and arteries into the capillaries. There the sub- 

 stances formed in the minute cells of the tissue by the de- 

 composition of their contents under the influence of the 

 vital force, diffuse into the blood, and here they meet the 

 oxygen contained in the corpuscles, and, uniting with it, 

 are burned, producing animal heat. Innumerable inter- 

 mediate products are formed in this process, but the final 

 result is 111 all cases the same. All the non-nitrogenous 

 substances yield carbonic acid and water; the nitrogenous 

 ones the same substances, and in addition urea, the char- 

 acteristic ingredient in urine. Urea is a crystallizable body 

 of comparatively simple composition, which together with 

 small amounts of other substances, contains all the nitro- 

 gen and part of the carbon and hydrogen of the albumi- 

 noids, from which it is derived, in the urine of herbiv- 

 orous animals it is, in part, replaced by hippuric acid. All 

 these oxydations take place in the cells and capillaries of 

 the body, and it is there, consequently, and not in the 

 lungs, that animal heat is produced." 



This latter theory, which seems the more philosophical, 

 does not change any of the practical conclusions hereto- 

 fore drawn in reference to the expenditure of food in the 

 production of animal heat. It therefore does not intro- 

 duce any practical new philosophy into the problem of 

 feeding and growing animals. 



URINARY ORGANS. These organs very important in 

 the animal economy are charged with eliminating from 

 the blood with the surplus water, the excrementitious nitro- 

 genous products resulting from the exercise of the vital 

 functions. 



The kidneys, the essential organs of urinary secretion, 

 are two glandular organs, situated in the abdominal cavity. 



3 



