74 



EXPERIMENTAL PHYSIOLOGY 



A, i.e. the length c d of fig. 68. 



a wave of velocity - will travel - x 



v v 



For if this time be t' during that time 

 t' cms. But at the end of the 



measured interval t' the wave is just leaving the fixed point. Hence 



A = - x t cms. 

 t 



Actual measurements show that this wave length is great as com- 

 pared to the general length of a muscle fibre, so that a single fibre 

 cannot present at any one instant all the phases representing a single 

 wave of contraction. Referring to our diagram it is as if the part 

 d e were the only piece available for observation, and we then had to 

 study the wave of thickening as it travelled over that portion. Thus 

 if we record the total changes at two positions on the fibre and the 

 time relations of those changes, we can then determine all the 

 characteristics of the wave. This we can do by the following 

 method : — 



Experiment 2. — Arrange the apparatus as for a simple twitch, fitting in 

 a pair of pin electrodes. Curarise a frog and dissect out a gracilis and semi- 

 membranosus preparation. Arrange this as shown in fig. 69. The prepara- 



Fig. 69. — Apparatus for Becording the Thickening of a Muscle at Two 

 Points, for the purpose of studying the Muscle Wave. 



tion m is pinned down to a cork base, at one end a pair of pin electrodes 

 being used. Two levers, l 1 and tr, are then arranged as in the figure. Each 

 lever consists of a light bar to which is jointed a light vertical bar termi- 

 nating in a flattened foot to rest on the muscle. Each lever is held on a 

 specially arranged block, a, which slides along a bar, d, and can be fixed in 

 any position by a screw, c. The axis of the lever is carried on a plate, b, 



