100 CHANGE IN FORM IN A MUSCLE WHEN IT CONTRACTS [CH. IX. 



prolongation of the period of relaxation ; marked by a secondary 

 rise, and sometimes by tremors. The second rise has received 

 various explanations, none of which can be regarded as satisfactory. 

 After repeated stimulation the veratrine 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 ; the nerve impulses, however, are so rapidly carried 

 to all the fibres that for practical purposes they all contract together. 

 But in a nerveless muscle, that is one rendered physiologically nerve- 

 less by curare, if one end of the muscle is stimulated, 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 next figure (fig. 122) represents one of the numerous methods 



FIG. 122. Arrangement for tracing the muscle-wave. (M'Kendrick.) 



that have been devised for this purpose. A muscle with long parallel 

 fibres, like the sartorius, is taken ; it is represented diagrammaticaliy 

 in the figure. It is stimulated at the end, where the two wires, 

 + and , are placed ; it is grasped in two places by pincers, which 

 are opened by the wave of thickening ; the opening of the first pair 

 of pincers (1) presses on a drum or tambour connected to a second 

 tambour with a recording lever (I'), and this lever goes up first ; the 

 lever (2') of the tambour connected with the second pair of pincers 

 (2) goes up later. If the length of muscle between the pairs of 

 pincers is measured, and by a time-tracing the delay in the raising 



