30 niYSIOLOGY OF MUSCLES AND NERVES. 



our present purpose — which is to discover whether or 

 not contraction takes place under certain circumstances 

 — it is hardly adapted. It may, therefore, be replaced 

 by another apparatus, arranged by du Bois-Eeymond 

 especially for experiments during lectures, and called by 

 him the muscle-telegraph. The muscle is fixed in a 

 vice ; its other end is connected by a hook with a 

 thread running over a reel. The reel supports a long 

 indicating- hand to which a coloured disc is attached. 

 The muscle in shortening turns the wheel and lifts the 

 disc ; and this is easily seen even from a considerable 

 distance. A second thread, slung over the reel, sup- 

 ports a brass vessel which may be filled with shot, so as 

 to apply any desired weight to the muscle. 



The influences which cause the contraction of the 

 muscle, such as pinching or smearing with acid, are 

 called irritants^ and the muscle is said to be irritable, 

 because contraction can be induced in it by these means. 

 The irritants already spoken of are mechanical and 

 chemical ; they labour under a disadvantage in that the 

 muscle, at least at the point touched, is destroyed, or 

 at least is so changed that it is no longer irritable. 

 There is, however, another form of irritant which is 

 free from this disadvantao^e. If the vice which holds 

 the upper end of the muscle and the hook to which the 

 lower end is attached are fastened to the two coatings 

 of a charged Kleistian or Leyden jar, the charge acts at 

 the moment at which the connection is formed, and 

 an electric shock traverses the muscle. At the same 

 instant the muscle is seen to contract, and the disc 

 passes abruptly upward. In order to repeat the experi- 

 ment it would be necessary to re-charge the Kleistian 

 jar. But similar electric shocks may be more con- 



