358 BIOLOGY. [Book v. 



a feeble continuous current that Helmholtz formerly determined 

 the duration of muscular contractions by means of very simple 

 experiments which had at the time a certain notoriety. He 

 made to pass along a frog's muscle detached from the animal 

 a current, which the fact itself of the contraction interrupted. 

 A galvanometer made it possible to appreciate to a certain degree 

 the duration of the different phases of contraction. The total 

 ■ duration of the contraction vi'as in these conditions 0",30:5, and 

 decomposed itself into three parts. In a first phase, which Helm- 

 holtz calls the pose, and which continued O''',20, there was no 

 appreciable effect, The action of electricity on the muscular 

 fibre is not therefore instantaneous. In this period of incu- 

 bation contraction succeeded; it continued 0",180, gradually 

 augmenting in intensity ; finally came a period of slackening, 

 which amounted to 0",105. If the contractions are thvs reiterated 

 a certain number of times, the muscle is fatigued, is exhausted : 

 it contracts with a force gradually decreasiag, and the duration 

 of the period of slackening grows longer and longer. 



The electrical current seems to act on the muscular fibre by 

 determining in it a change of molecular state. In effect, if the 

 current passes during a certain time without interruptions, we 

 see the muscle contract, especially at the commencement of the 

 passage of the current, and at the moment of its interruption. 

 On the other hand, the induced currents provoke a permanent 

 contraction. With an induced current of 32 interruptions a 

 second, Helmholtz obtained the tetanic contraction of the masseter 

 muscle. 



Not only the muscular fibre contracts under the iafluence of 

 electricity, but it is itself a sort of electric pile, as M. Dubois- 

 Reymond discovered. If, in effect, by the help of a conductor 

 and a galvanometer, we establish a communication between a 

 point of the surface of a muscular fibre and its section, we see 

 that there is an electrical current going from the exterior 

 surface to the section, and that this current ceases during the 

 contraction of the fibre. 



