20 LIFE IN NATUEE. 



in tracing the relation of decay to function, arises 

 from the admixture, with these changes, of the 

 opposite ones which constitute nutrition. The watch 

 is being wound up as it goes. Perpetually giving 

 off its force in function, this force is as perpetually 

 renewed from the world without. And the very 

 organs which are active by decay, are, perhaps at 

 the same moment, being restored by nutrition to 

 their perfect state. The disentangling of these pro- 

 cesses may well be allowed to have challenged man's 

 highest powers. 



Let us now endeavour to apply the conception we 

 have set forth to some of the animal functions, and 

 see how far it is confirmed or otherwise; and, if 

 true, to what point it carries us, and what further 

 questions it suggests. We conceive, in the active 

 structures of the body, a state of equilibrium very 

 easily disturbed, existing between the chemical 

 affinities of their elements, and a force which has 

 opposed these affinities; and that by the operation 

 of the stimuli which excite function, this equilibrium 

 is overthrown. 



Let us consider first the nervous system. Evi- 



