CHAPTER II 



RESPIRATION 



Eneegy is necessary to the operation of every machine, 

 whether it be an engine or a Uving organism. The engine 

 is supphed with energy directly or indirectly through the 

 intelligent action of a living organism ; the living organism 

 supplies itself with energy. In both cases the energy is ordi- 

 narily supplied by the same means, mainly by combustion 

 or oxidation, and the energy thus liberated is applied either 

 directly or indirectly in the same form. In the case of the 

 steam-engine the energy or power is applied indirectly, the 

 heat resulting from the combustion of fuel being utilized in 

 the conversion of inelastic water into perfectly elastic, com- 

 pressed, and hence active, steam. In the living organism 

 the energy resulting from combustion is applied directly in 

 the various kinds of work done by the living organism 

 either within or outside of its own body. 



Energy must be supplied to the engine for two purposes : 

 first, to overcome the resistance ( friction, inertia, etc. ) of 

 its own parts; and second, to enable it to overcome the 

 resistance offered by the materials upon and in which it 

 works. For two purposes also energy must be supplied by 

 the living organism for its own use: first, to continue liv- 

 ing; and second, to enable it to overcome the resistance 

 offered by the materials upon and in which it works. Let 

 us think first of the need of energy to continue living. Liv- 

 ing consists in maintaining the equilibrium between con- 

 structive and destructive influences. This implies work, in 

 the physicist's sense. So long as the constructive influences 

 overbalance the destructive the organism gains in some 

 way — grows, or increases in weight, or moves, or reproduces. 

 To gain thus, to do any of these things, the organism 

 needs energy. When the destructive influences overbalance 



