4 8 



ELEMENTARY TREATISE ON STOCK FEEDS AND FEEDING 



is necessary for the life of the tissues. Some of the waste 

 matters such as carbonic acid gas, water and organic sub- 

 stances, are passed off by the blood through the lungs in the 

 expired air. 



The changes the air undergoes in the lungs, on a water free 

 basis, are as follows: 



Oxygen 

 Per cent. 



Inspired air 20.96 



Expired air 16.00 



Nitrogen 

 Per cent. 



79.01 

 79-60 



Carbonic acid 

 Per cent. 



03 

 4.40 



The expired air contains about 5 per cent, less oxygen and 4 

 per cent, more carbonic acid than inspired air. Considerable 

 water is also given off with the expired air. 



The following table gives an idea of the extent of the elimina- 

 tion of wastes through the lungs of farm animals. 



AMOUNTS OF OXYGEN CONSUMED AND CARBONIC ACID PRODUCED 

 BY ANIMALS. 1 



The Kidneys may be regarded as the filters of the body, and 

 one of the channels by which waste and poisonous substances are 

 removed. or filtered from the blood, and passed off from the body 

 in the urine. The amount of blood passing to the kidney is 

 quite considerable; it has been calculated that in 24 hours, 146 

 pounds of blood will pass through the kidneys of a dog weigh- 

 ing 66 pounds. 



The Composition of Urine depends upon the class of animal; in 

 all herbivora, with certain minor differences, the urinary secre- 

 tion is much the same. 



1 Boussingault. 



