200 



MUSCLE AND NERVE. 



Detach the latter as far up to its junction with the sciatic 

 as you can, lifting the nerve by means of the muscle. The 

 tendinous slip from the gastrocnemius will have to be severed. 



Lifting the nerve by means of the muscle, so that neither 

 of them touch the frog support, stimulate with interrupter 

 shocks by the hand electrodes, and increase the strength of 

 the current until the gastrocnemius contracts. 



Great care must be taken that there is no chance of 

 leakage of the current directly to the muscle or its nerve. 



It is often difficult to convince oneself that leakage is 

 not the cause. In case the doubt should exist, apply a 

 ligature to the peroneal nerve as high up as possible, but 

 clear of the other structures of the thigh, and stimulate 

 again. If the ligature has been drawn sufficiently tight, 

 nerve transmission will be excluded, and leakage will offer the 

 only explanation of the phenomenon. 



Another way of doing this experiment, which can be easily tried whilst 

 both sciatics are at the disposal of the student at the time he is performing 

 the experiments on secondary contraction, is as follows : 



Lay a couple of cm of the ends of the two sciatics parallel and in 

 contact with each other upon a small block of paraffin, the latter being 



of such dimensions that it 

 will leave between itself and 

 the muscles on each side a 

 space of 3 cm . 



Stimulate the nerve near 

 one muscle. Lift the muscle 

 A from the plate (to prevent 

 leakage of current along the 

 plate to the opposite muscle) 

 and stimulate the nerve at S 



P paraffin block, W waxed paper, E electrodes. as far from the P araffin block 



as possible. If the nerves 



are in a normal condition induction shocks of considerable strength will 

 have to be applied before any effect is produced, and the limit of 

 these must not overstep the strength at which leakage occurs. 



w 



