CH. X.] 



THE MUSCLE-WAVE. 



125 



readily shown by dropping some warm salt solution* on to the muscle before 

 taking its curve. Too great heat (above 40 c.) induces heat rigor due to 

 the coagulation of the muscle-proteids. 



5. Effect / n-ratrlne. If this is injected into the frog before the muscle- 

 nerve preparation is made, the very remarkable result seen in the preceding 

 diagram is produced on stimulation ; there is an enormous prolongation of 

 the period of relaxation ; marked by a secondary rise, and sometimes by 

 tremors. After repeated stimulation this effect passes off, but returns after 

 a period of rest. 



The Muscle-Wave. 



The first part of a muscle which contracts is the part where 

 the nerve fibres enter ; but nerve impulses are so rapidly carried 



Fig. 149. - Arrangement for tracing the muscle-wave. (M'Kendrick.) 



to all the fibres that for practical purposes they all contract 

 together. But in a nerveless muscle, that is one rendered physio- 

 logically nervejess by curare, if one end of the muscle is stimu- 

 lated, the contraction travels as a wave of thickening to the other 

 end of the muscle, and the rate of propagation of this wave can be 

 recorded graphically. The above figure (fig. 149) represents one of 

 the numerous methods that have been devised for this purpose. 

 A muscle with long parallel fibres, like the sartorius, is taken ; it 



* Physiological saline solution used for bathing living tissue is a 07 to 0-9 

 per cent, solution of sodium chloride. 



