152 ON NERVE-EXCITATION BY THE NERVE-CURRENT. 



ascending (abterminal) in the end of a sciatic nerve which I had 

 divided above the knee. 



Just as it is possible to obtain secondary contraction or secondary 

 tetanus from any muscle which is set in action by excitation of its 

 nerve, when the nerve of the secondary is laid upon the muscle of 

 the primary preparation, so it is possible to obtain similar effects 

 in muscles in which contraction is produced by secondary action 

 derived from nerve. If I caused secondary contraction of the thigh 

 muscles as above described by the application of weak induction 

 currents to the extremity of the sciatic nerve at the knee, then a 

 second nerve-muscle preparation with its nerve lying upon the thigh- 

 muscles of the first frog gave what I may call 'tertiary' contraction, 

 and it passed into strong or * tertiary ' tetanus even when the currents 

 applied to the first nerve were only just sufficient to tetanise it. 



I have already pointed out above that the secondary contractions 

 from nerve are most easily obtained just after the plexus has been 

 divided. It follows that with the repetition of the experiment 

 upon otherwise quite unaltered preparations, the secondary action 

 diminishes more and more and finally ceases. This is not at all 

 due to fatigue alone, but chiefly to the decline of the nerve excita- 

 bility which had been previously enhanced owing to the section. 

 For even if one waits a little after division of the nerve without 

 subjecting it to excitation, and then excites, the secondary action is 

 weak or absent. With comparatively sluggish preparations a delay 

 of a few seconds is usually sufficient for this to be shown, but with 

 good preparations several minutes on an average are required. But 

 if a new transverse section is now made at the plexus, or if it is liga- 

 tured or crushed below the point where it was first divided, excitation 

 of the peripheral end of the nerve, when the muscles have come to 

 rest, gives, with good preparations, renewed and strong secondary 

 effects. In this way, and without altering the seat of peripheral 

 excitation, I have reproduced the secondary effects with the same 

 preparation after they had vanished, as many as six times. It how- 

 ever often happens with less excitable preparations, that a secondary 

 effect is obtained only after the first severance of the plexus. This 

 rapid disappearance of the heightened excitability consequent upon 

 section which is necessary to the success of the experiment, is the 

 real reason why these have escaped the attention of previous investi- 

 gators and especially of du Bois-Reymond, who must otherwise 

 certainly have met with them in the course of his experiments on 

 paradoxical contraction. 



