206 ANIMAL AUTOMATISM. [LECT. 



The property of muscle mentioned by Descartes 

 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 contrac- 

 tion, 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 muscular contraction on nerve holds good for the 

 higher forms of muscle, under normal circumstances ; 

 so that, although the structure of the various modifi- 

 cations of contractile matter has been worked out 

 with astonishing minuteness although the delicate 

 physical and chemical changes which accompany mus- 

 cular 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 short- 

 ening 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 per- 

 fectly 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- 

 Keymond 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 no means great, velocity, through 

 the substance of the nerve towards the muscle. 



