THE MUSCLE WAVE 73 



occurs simultaneously throughout the section upon which the recording 

 lever rests. 



The Muscle Wave. — We have seen that when a muscle contracts, 

 it passes through a series of phases, a latent period in which no 

 change of form occurs followed by a period of shortening, and this 

 again by one of relaxation ; and the same holds true for each fibre and 

 further for each constituent part of that fibre. If we, for the time 

 being, limit our attention to what is happening in a single fibre, it is 

 found that all parts do not pass through the different phases of their 

 contraction synchronously, but that the contraction travels along the 

 fibre in the form of a wave. A study of fig. 68 will make this clearer. 

 a b is supposed to represent a very long muscle fibre, which has been 

 stimulated at the point a, and as a result a wave of contraction, 

 represented by the bulging of the fibre between c and d, is travelling 

 towards B. At a somewhat later instant than the one drawn, the 

 condition of the fibre will be represented by the dotted lines, and the 

 front of the wave of contraction will have reached the point e. d has 

 then passed through about half of its phases, and at c the muscle has 

 returned to its initial form. The wave of contraction will in this way 



:b 



travel on until it reaches and has passed over b, when the whole fibre 

 will come to rest. In the study of a wave of such a nature we can 

 gain a full knowledge of it, if we can determine its following 

 characteristics : — 



(1) Its amplitude. 



(2) The rate at which it travels. 



(3) Its length. 



Its amplitude and general course can be ascertained by recording 

 the changes in diameter of a section of the fibre as the wave passes 

 over it. The method by which this is done has been carried out in 

 experiment 1. Next by measuring the time interval between the 

 first movement at d and the corresponding change at e we can deter- 

 mine its velocity after measuring the distance of e from d. Thus 

 suppose the distance d e to be I centimetres, and the time occupied 

 by the wave front in travelling from d to e to be t seconds ; then in one 



second the wave travels - cm., or in other words - is the velocity 



t t 



per second in centimetres. Lastly, if we determine the time the wave 

 takes to pass over any fixed point, we can determine its wave length 



