144 COSMIC PHILOSOPHY. [pt. ii. 



then it is a corollary from the persistence of force that as 

 much of this remaining motion as is taken up in changing 

 the positions of the units, must leave these by so much less 

 able to obstruct subsequent motion in the same direction."^ 



Now in the case of organic bodies, the enormously complex 

 molecular changes involved in nutrition are such as to aid 

 in the setting-up of the most perfect transit-lines. In an 

 inorganic mass the molecules have comparatively little 

 mobility, and they do not leave their connections from 

 moment to moment, to be instantly replaced by new molecules. 

 But the complex clusters of molecules which make up living 

 tissue possess immense mobility, and they are continually 

 falling to pieces and getting built up again. Consequently 

 the repeated passage of waves either of fluid matter or of 

 molecular motion along a definite line of least resistance, not 

 only changes the positions of the molecular clusters, but also 

 modifies the nutritive changes by which the temporary 

 equilibrium of the clusters is restored. Instead of a set oi 

 relatively homogeneous molecules, which are simply pushed 

 aside and then tend to oscillate back again, the advancing 

 wave encounters a heterogeneous edifice of molecules, which 

 tumbles to pieces and is instantly rebuilt. But in the re- 

 building the force exerted by the advancing wave has to be 

 expended ; and the result is that in the rebuilt cluster there 

 is a surplus tension exerted in the very direction in which 

 the waves are travelling. The transit-lines thus become far 

 more permeable than any which can be established in in- 

 organic bodies. The energy given out by the decomposing 

 cluster of molecules adds to the momentum of the wave ; so 

 that the line of least resistance becomes to a certain extent a 



^ Spencer, First Prv.iciplcs, p. 248. Thus, though Mr. Mill is justified in 

 inymg (Inmigural Discourse, p. 62) that " physiology is the first science in 

 vhich we [distinctly] recognize the influence of habit — the tendency of some- 

 ching to happen again merely because it has happened before" — yet, as we 

 hers see, the phenomena of habit are foreshadowed in the inorganic world. 

 An admirable instance of that continuity among phenomena whicJi is tvery. 

 where implied by the theory of evolution. 



