ANIMAL AUTOMATISM. 213 



The property of muscle mentioned by Descartes 

 now goes by the general name of contractility, but his 

 definition of it remains untouched. The long-contin- 

 ued controversy whether contractile substance, speak- 

 ing generally, has an inherent power of contraction, or 

 whether it contracts only in virtue of an influence 

 exerted by nerve, is now settled in Haller's favour; 

 but Descartes' statement of the dependence of mus- 

 cular contraction on nerve holds good for the higher 

 forms of muscle, under normal circumstances ; so that, 

 although the structure of the various modifications of 

 contractile matter has been worked out with astonishing 

 minuteness although the delicate physical and chem- 

 ical changes which accompany muscular contraction have 

 been determined to an extent of which Descartes could 

 not have dreamed, and have quite upset his hypothe- 

 sis that the cause of the shortening and thickening of 

 the muscle is the flow of animal spirits into it from 

 the nerves the important and fundamental part of 

 his statement remains perfectly true. 



The like may be affirmed of what he says about 

 nerve. "We know now that nerves are not exactly 

 tubes, and that "animal spirits" are myths; but the 

 exquisitely refined methods of investigation of Du- 

 bois-Eeymond and of Helmholz have no less clearly 

 proved that the antecedent of ordinary muscular con- 

 traction is a motion of the molecules of the nerve 

 going to the muscle; and that this motion is propa' 

 gated with a measurable, and by no means great, ve- 



