CONTRACTION AND WORK OF THE MUSCLES. 41 



CHAPTEE V. 



CONTRACTION AND WORK OF THE MUSCLES. 



The function of the nerve— Rapidity of the nervous agent— Measures of time 

 in physiology — Tetanus and muscular contraction — Theory of con- 

 traction — Work of the muscles. 



The experiments described in the preceding chapter show 

 us the muscle under artificial conditions, which may, perhaps, 

 induce us to suspect the results which they furnish. Can 

 this electrical agent, which has been employed to excite 

 motion, be assimilated to the unknown agent which the will 

 sends through the nerves to command the muscles to act? 

 And these artificially-produced movements, those brief shocks, 

 always similar if the conditions of the muscle be not changed, 

 in what do they resemble the motions commanded by the 

 will, which are so varied in their form and their duration ? 

 These objections deserve at least a brief discussion. 



The function of the nerve. When a nerve is excited by an 

 electric discharge, the electricity employed does not always 

 pass to the muscle in which the reaction takes place. The 

 shock is produced equally well when all propagation of the 

 electric current along the nerve is prevented, and it exhibits 

 itself equally when excitants of a quite different nature are 

 employed, for instance, pinching or percussion. Thus, the 

 excitant employed only excites in the nerve the transference 

 of the agent which is proper to that organ. Is not this 

 nervous agent itself electricity ? Notwithstanding the able 

 labours of the German physiologists, and especially of 

 M. Du Bois Reymond, science has not yet decided on that 

 subject. We know that electric phenomena are produced in 

 the nerve when it has been excited in a certain way, and 

 that their propagation throughout the nervous cord seems 

 to have precisely the same speed as that of the transference 

 of the nervous energy itself. How has this speed been 

 measured ? 



