iv ELECTROMOTIVE ACTION IN MUSCLE 417 



the other end of the frog's sartorius, connected at both ends with 

 the bones, the strongest excitation fails to produce any trace 

 of secondary action, notwithstanding a marked twitch of the 

 primary muscle and favourable position of the test-nerve, so 

 long as both (thread) electrodes are placed on the continuity of 

 the muscle, so that the lines of current must traverse it in a more 

 or less oblique direction at the point where they enter, as well 

 as leave, the muscle. No alteration of this negative result can 

 be detected, however much the muscle is extended. On the other 

 hand, secondary effects of great intensity may regularly be seen 

 with weak excitation of the primary muscle, if the galvanic 

 current leaves the muscle, at either end, by the natural uninjured 

 ends of fibres (51). It is sufficient to connect up one electrode 

 (kathode) with the stumps of bone, and to place the other, by 

 which the current enters, directly 011 the muscle. The secondary 

 twitch occurs with one direction of current only, while closure in 

 the other direction is followed by a vigorous twitch of the primary 

 muscle, without excitation of the second preparation. It is not 

 improbable that with simultaneous and equal excitation of the 

 collective ends of fibres on one side of the sartorius (as occurs 

 when the current leaves the muscle by one or the other end in 

 the longitudinal direction of the fibres), the wave of electrical 

 variation might be essentially distinguished from that which is 

 discharged with a more or less oblique exit of current through 

 an electrode placed at the side of the muscle. In every case, 

 however, we must assume that the excitatory wave discharged 

 by immersion of a fresh transverse section in conducting fluid, 

 owes its peculiar aptness for secondary action to the same condi- 

 tion as the wave produced by closure of an atterminal battery 

 current, so that the secondary inefficiency of the directly excited 

 curarised muscle is only apparent, and produced by purely external 

 conditions. 



With regard to these experimental results, it is very striking 

 that the position of the secondary nerve on the primary muscle 

 should have comparatively little influence on the consequences. 

 If, as it is impossible to doubt, this is an electrical excitation of 

 nerve by the action current of the primary muscle, two points 

 must be connected which present a considerable difference of 

 potential at a given moment. The most favourable position of 

 the secondary nerve is apparently that in which it lies upon the 



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