THE MUSCLE WAVE 



75 



which can be rotated round the screw e, and by that screw clamped in any 

 position to a. By movement along the horizontal rod d the levers can be 

 approximated or separated to suit the length of the muscle. By rotation of 

 the block a around the rod d the writing point of the lever can be raised or 

 depressed, and finally by rotation of the plate b the writing point can be 

 adjusted to the writing surface. By this apparatus we can record the changes 

 in thickness of the muscle at two points separated by a distance which can be 

 measured in millimetres. One lever is fixed near the pin electrodes, the other 

 as far away as is convenient. 



On recording a single twitch the tracing obtained is similar 

 to that of fig. 70. In this experiment the vertical levers rested on 

 the muscle at two points situated 16 mm. from each other, and 

 each therefore records the variations of thickness at those two points. 



The electrodes were placed immediately under the point on which 

 the upper lever rested. The time tracing is 200 per second. Hence 



Fig. 70.— The Thickening of a Muscle ; Curve I at 4 mm., and Curve II at 

 20 mm. from the spot stimulated. magnification, 8. tlme tracing, 200 

 per Sec. 



the measurements of the two latent periods are "0044 second and 

 •0094 second respectively. The difference is "005 second. Hence 

 the muscle wave travelled from the first lever to the second, a 

 distance of 16 mm., in -005 second ; therefore its rate was 3 - 2 metres 

 per second. The temperature of the room and hence of the muscle 

 was, in this experiment, 18° C. 



The time occupied by the total variation of thickness is seen for 

 both curves to be *085 second. Hence the length of the muscle 

 wave was - 085 x 3 - 2 metres = 27"2 cm. 



