THE LIVING WORLD 223 



But the blood after being thus impoverished, itself 

 requires replenishment, and this it obtains from the 

 nutritive material gathered from the alimentary canal 

 by the lymphatics, and subsequently poured into the 

 blood. 



Of all the functions of the body, that of respiration 

 is the most conspicuously necessary for the maintenance 

 of life, since the separate life of the cat begins with an 

 act of inspiration, while it is with an act of expiration 

 that it ceases. A short interruption of the process 

 necessarily results in death. In breathing, the air is 

 taken down into the lungs, and is thence again expelled 

 much poorer in oxygen but containing a much increased 

 quantity of carbonic acid, because the blood which conies 

 to the lungs from all parts of the cat's frame liberates 

 into them the excess of carbonic acid it has obtained 

 from the ultimate substance of the body and, in ex- 

 change, takes from the air in the lungs, the oxygen 

 requisite to supply that ultimate substance with the 

 oxygen it needs. 



Thus, in such an animal as the cat, there is both an 

 internal and an external process of respiration. The 

 former consists of the gaseous exchange which takes 

 place in the ultimate particles of the body. The latter 

 is the gaseous exchange which takes place in the lungs 

 themselves. 



Closely connected with respiration and nutrition is 

 the process named secretion, which is the special func- 

 tion of such organs as are called glands. Two most im- 

 portant organs of the cat's body are the kidneys, which 

 secrete and remove from the blood certain effete and 

 deleterious nitrogenous substances. The salivary glands, 

 liver and pancreas, pour their respective secretions (spittle, 

 bile, and pancreatic juice) into the alimentary canal, the 



