CHAPTEE XXIX. 



THE PHYSIOLOGY OF MIND. 



IN the chapter on the Direction of Development it has 

 ^- -- been stated that the fundamental differentiation in 



organs of animal development is that into the systems of organs 

 vegetative -^Jiich belong respectively to the vegetative and the animal 

 animal life. It is necessary for me to state over again part of 

 ^^^^' what I have already stated in that chapter, though I now 



approach the subject from a different point of view. The 

 organs of vegetative life essentially consist of an apparatus 

 for transforming matter; those of animal life essentially 

 consist of an apparatus for transforming energy. The 

 Contrac- fundamental attribute of the apparatus of animal life is 

 tihty, tlie contractility ; that is to say, the characteristic power of 

 mental muscular tissue to contract under the influence of a stimu- 

 of the°**^' lus, and in contracting to transform energy from the vital 

 latter. jnto the motor form : ^ in other words, to do work by con- 

 tracting. In those simple animals which have muscles but 

 no nerves, as especially the Hydrozoa, the stimulus under 

 which the muscles contract consists in the contact of food 

 or of some other foreign substance ; and such a stimulus, 

 if it is applied to one part of the animal's muscular 

 tissue, will slowly propagate itself; so that, if one tentacle 

 is iiTitated, the other tentacles will also contract. But in 

 those more highly organized animals which have a com- 

 plex nervous system, the stimulus rmder which the muscles 

 contract usually consists in a flow of nervous energy. The 

 difference between the action of muscles that usually con- 

 tract under a stimulus applied to themselves, and muscles 



^ See the chapter on the Dynamics of Life. 



