GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 43 



A much stronger contraction is obtained if the muscle be connected with 

 a large conductor, such as the human body, a large surface of tin-foil, a con- 

 denser, or the earth, for in the process of charging and discharging these 

 bodies there is a large flow of current through the preparation. Further 

 uniting the free pole of the secondary coil with the earth, because increasing 

 the difference in the potential of the two poles, increases the effect. In case 

 the free pole of the secondary coil be united to a large insulated conductor, 

 and this be brought near the nerve-muscle preparation without touching it, 

 the amount of excitation will be increased through what is known as " influ- 

 ence" action. For example, if the observer touch the free pole of the 

 secondary coil with one hand and approaches the other to the nerve prepara- 

 tion a larger contraction will be seen when the primary current is made or 

 broken. The effect produced on the preparation by the presence of a con- 

 ductor, which is suddenly given an electrostatic charge of opposite sign, as in 

 the case just mentioned, cannot be discussed here ; suffice it to say, it is 

 analogous to the influence exerted by the primary coil of an induction appa- 

 ratus on the secondary coil at the time that the battery current is made and 

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In all cases which we have cited the excitation of the nerve and muscle 

 was caused not by the change of electric potential, but by the sudden flow of 

 current accompanying the change. The exciting effect of the current depends 

 not only on the quantity of current, but also on the density of the stream. In 

 the unipolar experiments thus far described the nerve-muscle was brought 

 into connection with the secondary coil only at the point where the nerve 

 touched the electrode ; the electrical charge had to pass the length of the 

 nerve to reach the muscle, and all the charging current had to flow in a 

 dense stream the length of the nerve. This can be obviated by greatly 

 enlarging the electrode and letting it come in contact with a large part of 

 the nerve and muscle — e. g., by using for an electrode a piece of thin tin-foil, 

 or better gold-foil, and applying this to a large part of the surface of the 

 nerve and muscle (see Fig. 22). By this arrangement the change in electric 

 potential will be transmitted practically instantaneously throughout the good 

 conducting foil, and the nerve and muscle will be charged from a vast 

 number of points of contact and will at no part be subjected to a large quan- 

 tity of electricity flowing in a dense stream. The whole of the nerve-muscle 

 preparation will be charged, as before, to the potential of the pole witli which 

 it is connected, but it will not be stimulated. That the nerve-muscle receives 

 an electrostatic charge under the above conditions can be readily observed by 

 approaching the finger to the muscle at the time that the primary circuit is 

 closed or opened. If the body of the observer has a large capacity, a large 

 amount of current will flow through the nerve and muscle to the finger. This 

 current will pass in a dense stream from the muscle at the point of contact 

 with the finger, and the muscle-fibres at this part, because subjected suddenly 



1 Hermann: Handburh der Physiologic, Bd. ii. Thl. 1, S. 87 ; Biedermann : Electro-physiology 

 (translated by F. A. Welby), 1897, vol. ii. p. 219. 



