60 THE DATA OF BIOLOGY. 



loids constituting muscle may be thus changed by a nervous 

 discharge: resuming their previous condition wlien the dis- 

 charge ceases. And it is conceivable that by structural 

 arrangements, minute sensible motions so caused may be 

 accumulated into large sensible motions. 



§ 23. But the truths which it is here our business espe- 

 cially to note, are independent of hypotheses or interpreta- 

 tions. It is sufficient for the ends in view, to observe that 

 organic matter does exhibit these several conspicuous re- 

 actions when acted on by incident forces. It is not requisite 

 that we should know how these re-actions originate. 



In the last chapter were set forth the several modes in 

 which incident forces cause re-distributions of organic matter ; 

 and in this chapter have been set forth the several modes in 

 which is manifested the motion accompanying this re-distri- 

 bution. There we contemplated, under its several aspects, 

 the general fact that, in consequence of its extreme instability, 

 organic matter undergoes extensive molecular re-arrange- 

 ments on very slight changes of conditions. And here we have 

 contemplated, under its several aspects, the correlative general 

 fact that, during these extensive molecular re-arrangements, 

 there are evolved large amounts of energy. In the one 

 case the components of organic matter are regarded as fall- 

 ing from positions of unstable equilibrium to positions of 

 stable equilibrium; and in the other case they are regarded 

 as giving out in their falls certain momenta — momenta that 

 may be manifested as heat, light, electricity, nerve-force, or 

 mechanical motion, according as the conditions determine. 



I will add only that these evolutions of energy are rigor- 

 ously dependent on these changes of matter. It is a corollary 

 from the primordial truth which, as we have seen, underlies 

 all other truths, {First Principles, §§ G2, 189,) that whatever 

 amount of power an organism expends in any shape, is the 

 correlate and equivalent of a power which was taken into it 

 from without. On the one hand, it follows from the persist- 



