204 



PHYSIOLOGY 



is taken, stimulated at one end, and the thickening of the muscle recorded by 

 means of two levers placed one near the exciting electrodes and the second 

 at the other end of the muscle, as shown in the diagram (Fig. 64). The 

 difference between the latent periods of the two curves represents th'e time 

 taken by the contraction wave in travelling from a to b. By measurements 

 carried out in this way it is found that the rate of propagation of the con- 

 traction in frog's muscle is 3 to 4 metres per second ; in the muscle of 

 warm-blooded animals it may amount to 6 metres. 



FIG. 04. Diagram of arrangement for recording the contraction wave in a 

 curarised sartorius. 



The actual duration of the shortening at any given point is necessarily 

 smaller than that of the whole muscle, and amounts in frog's muscle to only 

 0-05-0-09 sec., about half the duration of the contraction of a whole muscle 

 of moderate length. The length of the wave is obtained by multiplying the 

 rate of transmission by the duration of the wave at any one point. It varies 

 therefore in frog's muscle between 3COO x -05 ( = 150) and 4CCO x -09 

 ( = 360) millimetres. Thus the muscle fibres in the frog are much too short 

 to accommodate the whole length of the wave, and the contraction of the 

 whole muscle must be made up of the summated effects of the contraction 

 wave as it passes from point to point. Hence the longer the muscle, the 

 more must the contraction be lengthened by the time taken up in propagation 

 from one end to another. 



