ix ELECTRICAL EXCITATION OF NERVE 221 



time the muscle-nerve was touched there was excitation, varying 

 in strength with the distance between the plates, and susceptible 

 with a suitable lead-off (by a fine metal point) of very exact 

 localisation. In this case also, the break shocks only took effect. 

 Schiff and Fuchs (60) also obtained unipolar action without 

 induction, with the exclusive action of static electricity. They 

 carried the charges from the ends of an open circuit into a large 

 conductor, or the plates of a condenser, and then led them 

 through an excitable nerve. The following experiment by 

 Eosenthal (60) is also suggestive. A nerve-muscle preparation 

 insulated on a glass plate, upon which the nerve and muscle lie 

 in a trough, is suddenly brought near a charged conductor, held 

 by an insulated glass handle, on which a small twitch may occur 

 when the end of the nerve is proximal to the conductor, never, 

 on the other hand, when the conductor is brought near the 

 muscle end. But if in the last case the nerve is led off by 

 contact, or even connected with an insulated conductor of any 

 size, there is always marked excitation. 



The theory of unipolar excitation, of which we have thus 

 been considering some instructive instances, was essentially 

 developed by du Bois-Eeymond, who showed that it depended 

 upon the electrical potential at the two free ends of an induction 

 coil. At the moment of opening or closing the primary circuit, 

 an open secondary circuit represents, as it were, an open battery, 

 with free electricity at its two ends. If each pole of the secondary 

 coil is connected respectively with the nerve of a frog's leg, loth 

 preparations twitch if one of them is led off to earth because 

 both nerves are traversed by the flowing electricity, in opposite 

 directions. The same thing of course takes place when only 

 one metal pole is connected with the nerve of a preparation, the 

 lead-off being either from the leg or from the other free pole. 

 The electricity necessary to charge the leg always flows through 

 the nerve, and thus excites it. Obviously, the intensity of 

 the excitation depends in first degree upon the amount of 

 electricity flowing through the nerve increasing accordingly 

 with difference of potential, approximation of coils, and lead-off 

 from free pole. Augmentation of the electrical capacity of the 

 leg produces the same result. To this is due the favourable 

 effect of connecting up a unipolar preparation with conductors 

 of a larger surface (human body, etc.), as well as the approxima- 



