CHAPTEH YIII. 



THE cat's organs of respiration and secretion. 



^ 1. The FUNCTION OF RESPIRATION IS that One of all the func- 

 tions of the body which is the most conspicuously necessary for the 

 maintenance of life. Let this function be interrupted in the adult 

 cat* but for ten minutes (v^^hether by external obsti'uction, the 

 absence of the requisite gaseous material, or by paralysis of the 

 respiratory organs), and death is the necessary result. It has been 

 already mentioned in the chapter on Alimentation, that oxygen is 

 taken into the body through the lungs ; and it has also_ been 

 stated — in the last chapter — that the blood undergoes a conspicuous 

 change (from its purple venous state to its scarlet arterial condition) 

 duiing the pulmonary circulation. This change is due to tho 

 absorption by the blood, and consequent increase of its supply, of 

 oxygen, and to the elimination from the blood of more or less of its 

 carbonic acid. 



It is this interchange of gases between the living animal and the 

 surrounding air which constitutes "breathing," or respiratioji. But 

 the animal we are considering may be said to have two processes of 

 respiration — one " internal," the other relatively " external." Such 

 is the case, because the oxygen received into the blood does not 

 remain there, but is carried by the circulation to the remotest 

 recesses of the body, where it unites with that body in its innermost 

 substance or parenchyma. 



Similarly, the carbonic acid which the blood sets free docs not 

 originate in the blood, but is given forth into the blood from all the 

 ultimate particles of the same parenchyma. 



Thence, the blood gathers it, and conveys it outwards for dis- 

 charge in the lungs. The blood, therefore, is a great distributor, 

 which both gives out and takes in oxygen and carbonic acid at 

 either end of its course, from the lungs to the innermost body 

 substance. 



In the lungs it gives out carbonic acid, and takes in oxygen (as 

 has just been said) ; while in the inmost recesses of the body it 



* In the chapter on Development it 

 will be explained how it is that inter- 

 ruptiou in the process of J-espiration is 



not so rapidly fatal in the kitten as it is 

 in the adult cat. 



