CHAPTER IV 



RESPIRATION 



From the knowledge which we have gained concerning the 

 nature of response in animals we have learned that the utilisa- 

 tion of oxygen is an essential feature of the processes by 

 which effector mechanisms are restored to their original 

 condition after a state of induced activity. The intake of 

 oxygen by the organism will be our first consideration in 

 dealing with the sources of vital energy, since the necessity 

 of oxygen for the maintenance of animal life is a universal 

 phenomenon. 



Under the heading of respiration it is customary to include 

 not only the intake of oxygen, but the removal of carbon dioxide 

 which is associated with it. Except where we have to deal 

 with tissues like ciliated epithelium in immediate contact with 

 the external world, the intake of oxygen involves : (i) the 

 absorption of oxygen by the tissues from the body fluids ; 

 (ii) the absorption of oxygen by the body fluids from the 

 external medium. It will be convenient (though less logical) 

 to treat the latter before passing on to the special arrange- 

 ments for the transport of oxygen to the tissues by the 

 body fluids, and CO2 from the tissues to the external 

 medium. 



(a) Localised Respiration. — In many animals the absorp- 

 tion of oxygen takes place to some extent over the entire surface 

 of the body. Though this is not true of mammals, birds, and 

 probably reptiles, it is certainly the case with most cold- 

 blooded vertebrates. Thus Paul Bert showed that the axolotl 

 larva of the Mexican salamander survives after removal of both 



64 



