162 MUSCLE AND NERVE CURRENT. 



body and converted into heat during rest. When the muscle- 

 (or nerve) acts the current immediately ceases, or undergoes 

 the negative variation. This is not, as C. B. Eadcliffe explains,, 

 a change to a current of negative electricity, but simply a 

 weakening or exhaustion of the strength of the current almost,, 

 but not quite, down to zero. This negative variation is so- 

 constant that, in default of the visible sign of action which the 

 muscle gives by contraction, it is taken as a sign in the nerve 

 that it is in the acting state. " Nothing is as yet certainly 

 ascertained respecting the quantitative relation of the negative 

 variation to heat production and mechanical work. The varia- 

 tion takes place in the stage of latent irritation (of Helmholtz), 

 and only occupies a very short time, i.e., 0.001 of a second " 

 (Bezold). Hermann, p. 239. The stage of latent irritation 

 is the period which elapses between the application of the 

 stimulus and the contraction of the muscle. A certain time 

 thus appears to be required for the change from the pro- 

 duction of the electric current to that of work. The 

 muscle current belongs exclusively to the living muscle, 

 and gradually diminishes after somatic death till it quite 

 ceases when rigor mortis comes on. It is also stronger the 

 more functionally capable the muscle is, and is diminished by 

 privations, poisons, and all agents which injure or destroy life. 

 The same applies to the nerve current. 



These are the chief facts of importance in respect to 

 animal electricity, and they form a slender foundation 

 for tbe theory of the identity of that force with the 

 nerve force. The disappearance of the current on the- 

 action of the muscle does not necessarily show that the- 

 motor force of the muscle was electricity, for the same- 

 would happen, whatever the nature of the nerve force, 

 if it were directly transformed into mechanical work 

 instead of into electricity as it is in the resting 

 muscle.* The theory, in fact, rests more on analogical 



* The negative variation on the occurrence of contraction would at 

 first sight appear to speak in favour of Dr. C. B. Radclifie's ingenious 



