THE MECHANICAL CHANGES OF MUSCLE 223 



the stimulus and the moment at which the first mechanical change 

 makes its appearance. 



The relaxation of muscle is helped by a moderate load, and in a 



Fia. 56. Burdon Sanderson's method for photographic record of muscle- 

 twitch. The exciting shock is sent into the muscle by the wires 

 d and d'. 



normal condition is complete. It is not active that is to say, is not 

 due to a contraction in the transverse direction but is a passive 

 effect of extension and elastic rebound. This may be shown by 



FIG. 57. Photographic record of muscle-twitch. (B. SANDERSON.) The 

 upper curve is the movement of the muscle, the middle curve the signal 

 showing the moment of excitation, and the lower curve is that of a 

 tuning-fork vibrating 500 times a second. 



allowing a muscle to contract while floating on mercury. The sub- 

 sequent lengthening on relaxation is very incomplete. 



Even with the most careful arrangements for securing isotonicity 

 in the record of the contraction there is probably a certain amount of 



