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METHODS OF ELECTRICAL STIMULATION 73 



ing experiment shows that even very small sur- 

 faces will suffice. 



4. On a carefully dried, clean glass plate lay 

 four nerve-muscle preparations. Let the nerve 

 of the first rest on a single wire the other end of 

 which is fastened in one of the binding posts of 

 the secondary coil. Place the end of the second 

 nerve on the tendon of the muscle of the first 

 preparation, the third on the second tendon, and 

 the fourth nerve on the tendon of the third. 

 Eemove the secondary coil some distance (a few 

 centimetres) from the primary, and set the in- 

 ductorium in action. Gradually approximate 

 the coils. 



As the tension at the ends of the secondary 

 wire increases by the approximation of the coils, 

 the first preparation will contract. On further 

 approximation, the first and second; then the 

 first, second, and third ; and finally all four will 

 contract. 



This instructive experiment shows that when 

 the conducting surface is small, as in the present 

 instance, the unipolar action is greater on the 

 parts nearer the secondary wire than on parts 

 farther away. The danger of unipolar action on 

 tissues lyig near the electrodes in ordinary 

 artificial stimulation of nerves and muscles in 

 situ is obvious. 



