v ANIMAL AUTOMATISM 207 



now goes by the general name of contractility, 

 but his definition of it remains untouched. The 

 long-continued controversy whether contractile 

 substance, speaking 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' state- 

 ment of the dependence of muscular contraction 

 on nerve holds good for the higher forms of muscle, 

 under normal circumstances; so that, although 

 the structure of the various modifications of con- 

 tractile matter has been worked out with astonish- 

 ing minuteness although the delicate physical 

 and chemical changes which accompany muscular 

 contraction have been determined to an extent of 

 which Descartes could not have dreamed, and 

 have quite upset his hypothesis 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 state- 

 ment 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 Dubois-Reymond and of Helmholz have no less 

 clearly proved that the antecedent of ordinary 

 muscular contraction is a motion of the molecules 

 of the nerve going to the muscle ; and that this 

 motion is propagated with a measurable, and by 



