0-> 



indefinitely. In the connection the two currents go in 

 the same direction, but break it and the secondary cur- 

 rent returns in a contrary direction. In this way the 

 two currents '"an be made to pass forward and back- 

 ward, with regularity of a weaver's shuttle. It is 

 worthy of note that the return current, induced by the 

 break of connection, is much stronger in this parallel 

 Avire, on the *' home stretch," than is that running in the 

 same direction as the fluid in the connecting wire. If 

 a number of insulated wires are coiled S2)irally round 

 the primary wire, instead of running parallel to it, not 

 only will these intermittent currents be produced, but 

 also an extra or third current is produced in all the 

 wires, no doubt induced by the magnetic influence of 

 one upon the other. These facts will be of importance 

 when we come to consider nerve influence, especially 

 when we find that the larger the wire, the greater the 

 number of spirals, the more powerful is the magnetic 

 influence. The larger the healthy nerve is, the more 

 capable it is to transmit magnetic power, in proi)orti(ni 

 to its size. Apparent exce])tions do not violate this 

 law. The point of a ])in makes a limited impression 

 on the end of my finger, yet, small thougli the injury 

 may be, the nerve disturbance is consideral)le. There 

 is no reason to believe that the irritation is confined to 

 the fibre of nerve injured ; nor that the influence travels 

 to the nearest ramifications, and ft'om them sends mes- 

 saijes of alarm to the neiij^hborinii* surface, as well as to 

 the seat of sensation. According to the laws above 

 mentioned, synchronous impulses can be sent through 

 adjacent nerves, by induced electric currents, and at 

 the cessation of excitation a powerful return current i» 

 set up, which ])roduces the contraction of muscles, even 

 before the will has power to act. I need scarcely add 

 that a large number, if not all, of jihysicid automatic 



