94 



poison, /. e., when all reflexes cease, expose both sciatic nerves 

 as far up as the vertebral column and as far down as the knee. 



Stimulate the rig-ht sciatic nerve. There is no contrac- 

 tion. Stimulate the right g'astrocnemius muscle ; it contracts. 

 The poison has therefore not affected the muscle. 



Stimulate the left sciatic nerve above the lig-ature, the 

 left leg- contracts. The poison has not affected the nerve 

 trunk. The nerve impulse is blocked by the curare, in all 

 probability by paralysis of the end plates of the motor nerves 

 within the muscle. Apply several drops of a strong solution 

 of curare to the left gastrocnemius, and after a time stimulate 

 the left sciatic nerve ; there should be no contraction, but on 

 stimulating the muscle directly, contraction occurs. 



333. Bernard's Method. Two nerve-muscle preparations are made. The 

 nerve of one (A) is immersed 20 to 30 minutes in a solution of curare in a 

 watch-glass. The muscle of the other preparation (B) is immersed in the curare 

 in another watch-glass for an equal length of time. On stimulating the nerve 

 of A, its muscle contracts ; on stimulating the nerve of B, its muscle does not 

 contract, but the muscle contracts when it is stimulated directly. In A, although 

 the poison is applied directly to the nerve trunk, the nerve is not paralyzed. 



334. Relative Kxcitability of Muscle and of Nerve. 

 Determine the minimal break shock which will cause a muscle 

 twitch through the sciatic nerve, and then apply the same 

 stimulus to the gastrocnemius muscle directly. It will not 

 cause contraction. 



Slide the S coil nearer to the P coil until the stimulus is 

 strong enough to cause the muscle to contract, and note the 

 difference in strength required. 



This experiment does not permit of the conclusion that 

 the muscle possesses independent irritability, as the nerve 

 terminations in the muscle are not excluded. (See Curare 

 Experiment. ) 



335. Changes in the Excitability of a Nerve 

 When Dying. Dissect out the sciatic nerve of a frog, but do 

 not cut it from its connection with the myel. Place under its 

 whole length a strip of thin rubber or a piece of waxed paper 

 and keep the nerve moist with the saline solution. 



Carefully raise the nerve with the glass rod or camel's 

 hair brush and explore it from one end to the other with 

 minimal single induction break shocks, the effect of which 

 have been tested first at the middle of the nerve, and note if 



