60 THE DATA OF BIOLOGY. 



loids constituting muscle may be thus changed by a nervous 

 discharge: resuming their previous condition when the dis- 

 charge ceases. Arid 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, 62, 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- 



