i GENEKAL PHYSIOLOGY OF MUSCLE 23 



thickness of the particular portion of the muscle to which the 

 myograph is applied. 



The rate of propagation of the contraction wave can be calcu- 

 lated from the interval between the contraction of two different 

 points of an isolated muscle, traced by two myograph levers placed 

 on the muscle at a known distance from each other, and writing 

 on the same drum. The sartorius muscle of the frog, in which 

 the fibres were parallel to one another, is the most suitable for 

 this purpose. Before dissecting it out, the frog should be curarised 

 to eliminate the action of the stimulus upon the inframuscular 

 nerves. When an induced shock is applied to one end of the 

 muscle, the contraction spreads in wave-form to the other end, at 

 a velocity which can be calculated by means of the two curves. 



Fig. 16 shows that the second curve rises about 0'06 sec. 

 after the commencement of the first curve : in passing over the 



FIG. 16. Two myograms of thickening from the same frog's muscle, obtained by applying two 

 pinces imjographiiiu.es at a distance of 15 mm. to measure the velocity of the excitation wave. 

 (Marey.) Time tracing in T sec. 



part of the muscle between the two myographs the wave of con- 

 traction therefore occupied 0'06 sec. As the distance between the 

 two levers was 15 mm., the wave travelled at a rate of about 1 m. 

 per second. 



The length of the wave can also be calculated from the 

 duration of the thickening of the fibres (in Fig. 16 about seven 

 vibrations of the tuning-fork = 0*07 sec.), and from the rate at 

 which the wave is propagated. Bernstein stated that the duration 

 of the twitch in any segment of the muscle (which must be dis- 

 tinguished from the duration of the twitch of the whole muscle, 

 which usually takes longer) is from 0*05 to 01 sec. Assuming 

 Bernstein's calculations of the rate at which the wave travels 

 3-4 in. per second, to be correct then the length of the wave, or 

 the part of the muscle over which it passes in O'05-O'l sec., is on 

 an average 200-300 mm. 



As the length of each muscle fibre rarely exceeds 40 mm. the 

 entire length of each fibre is usually involved in the contraction. 

 It is only at the beginning and towards the end of the contraction 

 that one or other end of the fibre is not active ; throughout the 



