34 



EXPERIMENTAL PHYSIOLOGY 



in the secondary circuit. Describe an abscissa, and mark the 

 point of stimulation as in previous experiments by raising the end 

 of each lever by the hand when the projecting pin on the drum just 

 touches the vertical needle (see p. 29), making use of the slop. Then 

 take the two tracings of the contraction of the muscle, letting the 

 drum revolve once only, and removing the levers the instant the 

 curves are completed. The difference of latency of the two curves 



PIG. 35. DIAGRAM OP AEBT'S EXPERIMENT FOR RECORDING THE MUSCLE WAVE, a, Z>, LIGHT 

 STRAW LEVERS RESTING' ON THE MUSCLE, WHICH is CURARIZED ; k, V, KEYS IN PRIMARY 

 AND SECONDARY CIRCUITS. 



represents the time which it has taken for the wave of contraction 

 to pass along the length of the fibres which intervene between the 

 two places on which the levers rest. Take a tuning-fork tracing, and 

 measure this time, and from it and the length of muscle traversed by 

 the wave (measure with compasses) calculate the rate of propaga- 

 tion of the muscle wave per second. 



It is essential for the success of this experiment that the muscles used should 

 have most of their fibres running longitudinally and parallel with one another. 

 If very large frogs are obtainable the two sartorius muscles may be used with 

 advantage instead of the adductor preparation described. 



