476 MOVEMENTS. 



one-fifth, by contracting the muscles as forcibly as pos- 

 sible. 1 



The nerves are not capable of conducting an artificial 

 stimulus for an indefinite period, nor are the muscles able 

 to contract for more than a limited time upon the reception 

 of such an impression. The electric current may be made 

 to destroy for a time both the nervous and muscular irrita- 

 bility ; these properties becoming gradually extinguished, 

 the parts becoming fatigued before they are completely 

 exhausted. Precisely the same phenomena are observed in 

 the physiological action of muscles. When a muscle is 

 fatigued artificially, a tetanic condition is excited more and 

 more easily, but the intensity of the contraction proportion- 

 ally diminishes. 2 Muscles contracting in obedience to the 

 will pass through the same stages of action. It is probable 

 that constant contraction is excited more and more easily as 

 the muscles become fatigued, because the nervous force is 

 gradually diminishing in intensity. It is certain that the vigor 

 of contraction at the same time progressively diminishes. 



Electric Phenomena in the Muscles. It was ascertained 

 a number of years ago, by Matteucci, that all living muscles 

 are the seat of electric currents ; not very powerful, it is true, 

 but still sufficiently marked to be detected by ordinary gal- 

 vanometers. It is difficult, in the present state of our 

 knowledge, to appreciate the physiological significance of 

 this fact, and we will therefore merely allude to the chief 

 electric phenomena that are ordinarily observed, without at- 

 tempting to follow out the elaborate and curious experi- 

 ments since made by Du Bois-Reymond and others. One 

 of the most simple methods of demonstrating this current is 

 to prepare the leg of a frog with the crural nerve attached, 

 and apply one portion of the nerve to the deep parts of an 

 incised muscle and the other to the surface. As soon as the 

 connection is made, a contraction of the leg takes place. 



1 MAREY, op. cit., p. 455. 2 Idem., p. 378, et scq. 



