48 PRACTICAL PHYSIOLOGY 



CHAPTER IX. 

 THE RELATION BETWEEN MUSCLE AND NERVE. 



THE motor nerves by means of their end-plates are so intimately con- 

 nected with the muscle-fibres that it is impossible to stimulate the 

 muscle-substance alone by the direct application of a pair of electrodes 

 to the intact muscle. The question, therefore, arises whether muscle 

 possesses independent excitability, whether it can respond to a stimulus 

 without the intervention of its nerve. The development of muscle 

 from protoplasm, which is contractile and excitable although possessing 

 no nerves, would suggest that muscle itself is excitable and can respond 

 to a stimulus. This can be shown, for the fully developed muscle, after 

 its nerve has been paralysed by the action of a drug. 



Curare 1 is an alkaloid used as an arrow-poison by some natives of 

 South America. The following experiments show that it paralyses the 

 terminations of the motor nerves, but that the muscle still responds to 

 direct stimulation : 



(i) Two watch-glasses are almost filled with a 1 per cent, solution of 

 curare in normal tap-water saline. Two muscle and nerve-preparations 

 are made, care being taken to bisect the lower portion of the vertebral 

 column and thus obtain the entire length of the sciatic nerve. The 

 excitability of the nerve and of the muscle in the case of each preparation 

 is tested by the determination of the minimal stimuli. Then the nerve 

 of preparation A is placed in one watch-glass full of the poison, but its 

 muscle is left outside upon a piece of filter-paper moistened with normal 

 tap-water saline. The gastrocnemius muscle of the preparation B is 

 .placed in the solution of the drug and its nerve upon the damp filter- 

 paper (Fig. 50). Stimulation of the nerve B will soon produce no 

 contraction, even if the strongest induction-shocks be used ; on the 

 other hand, an examination of the nerve A will show that its 

 excitability has practically undergone no decrease. Stimulation of the 

 muscle B which has been exposed to the action of the drug readily 

 produces a contraction. The poison, therefore, must act upon some 

 portion of the terminations of the nerves, probably upon the end- 

 plates, for both muscle-substance and nerve-trunk retain their excita- 

 bility even after long exposure to the drug. 



Muscle will contract on direct stimulation even after its nerves have 

 degenerated. This experiment, however, is not suitable for a class, for 

 it would be necessary to keep the animal alive for two or three weeks 

 in order that the nerve-fibres might completely degenerate. 



*It is prepared from various plants of the genus Strychnos. 



