MUSCULAR CONTRACTION. 541 



nerve or a muscle does not induce muscular contraction ; and it is only when the cur- 

 rent is closed or broken, that any action is observed. But if we employ statical elec- 

 tricity, a muscular spasm occurs at every discharge, proportionate, in some degree, to 

 the power of the excitation. If the discharges be very frequently repeated, or if a gal- 

 vanic current be applied, broken by an interrupting apparatus, the spasms follow each 

 other in quick succession. In experimenting upon the muscles of the frog, with a regis- 

 tering apparatus, Marey has found that, with a gradual increase in the rapidity of the 

 electric shocks, the individual muscular spasms become less and less distinct, and that 

 finally the contraction is permanent. His diagrams show well-marked spasms under 

 ten excitations per second, a more complete fusion of the different acts with twenty 

 per second, and a complete fusion, or tetanus, with twenty-seven per second. When 

 the contraction had become continuous, there was an elevation in the line, showing 

 increased power, as the excitations became more and more frequent. This is precisely 

 the kind of contraction that occurs in the physiological action of muscles. Although 

 the nervous force is not by any means identical with electricity, either the interrupted 

 galvanic current or a succession of statical discharges is capable of producing a muscular 

 action very like that which is involved in voluntary movements. The observations 

 of Marey, showing that the intensity of what he terms artificial tetanic contraction 

 is in proportion to the rapidity with which the electric discharges succeed each other, 

 are exceedingly interesting in their practical applications ; and an important question at 

 once arises regarding the nervous force that excites voluntary motion. Is this a series of 

 discharges, as it were, producing a power of muscular contraction in exact proportion to 

 their rapidity ? In view of the experiments just cited, this theory is very probable ; and 

 it is certain that the effect of a rapid succession of electric discharges almost exactly simu- 

 lates the normal action of muscles. That vibrations, more or less regular, actually occur 

 in muscular contraction, has been settled beyond a doubt by the researches of Wollaston, 

 Ilaughton, and more lately by Helmholtz, the latter having recognized a musical tone in 

 contracting muscles, exactly corresponding with the number of impressions per second 

 made upon the nerve. He farther devised an ingenious method of recognizing the tone, 

 by filling the ears with wax and contracting the temporal and masseter muscles. Marey 

 has found, in repeating this experiment, that the tone may be changed by modifying the 

 intensity of the muscular action. With the jaws feebly contracted, a grave sound is 

 produced, and this can be raised one-fifth, by contracting the muscles as forcibly as 

 possible. 



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 excitation. The electric current may be made to destroy for a time both the 

 nervous and muscular irritability ; and these properties become gradually extinguished, the 

 parts becoming fatigued before they are completely exhausted. Precisely the same phe- 

 nomena 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 proportionally diminishes. Muscles contracting in obedience to an effort of 

 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 gradually diminishes 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, which are not very 

 powerful, it is true, but still are sufficiently marked to be detected by ordinary galvanome- 

 ters. It is difficult, in the present state of our knowledge, to appreciate the physiological 

 significance of this fact, and we shall therefore merely allude to the chief electric phe- 

 nomena that are ordinarily observed, without attempting to follow out the elaborate and 



