164 ELECTRO-PHYSIOLOGY CHAP. 



ments on nerve, relating to preparations enclosed for several 

 hours in a moist chamber at the temperature of the room ; 

 excitability being in consequence much diminished. Immediately 

 after dividing such a nerve near the electrode distal to the muscle, 

 a weak descending current will discharge a break twitch, along 

 with the make twitches, which are,not essentially altered in magni- 

 tude by the incision. The ascending closure twitch may indeed 

 appear rather larger than before, but is nothing like its original 

 height. It thus appears that other factors come into play near 

 a point of section, which favour the appearance of the opening 

 twitch independently of augmentation of excitability. 



At this point we must ask whether the opening excitation 

 of the nerve is conditioned to the same extent as the closing 



o 



excitation by its state of excitability at the moment. Whether, 

 in other words, it is possible to produce opening twitches with 

 weak currents, by artificially increasing the excitability to closure 

 stimuli. 



This question might seem to be already decided by the experi- 

 ments of Kosenthal and v. Bezold (32) to which we have fre- 

 quently alluded, since in these observations the opening twitch 

 appears even with weak currents, owing to the alleged rise of 

 excitability during the spontaneous dying of the nerve. But 

 this appears to occur only under certain conditions. At all events, 

 Biedermann has been unable, on repeating the experiment, to dis- 

 cover the regular succession of the three stages of the so-called 

 law of contraction in moribund nerve, on exciting any point with 

 uniformly weak currents provided the preparation was enclosed 

 in a moist chamber, and carefully preserved from injury, and 

 especially from evaporation. As was pointed out above, even 

 the primary stage of increased excitability described by Rosen- 

 thai in the moribund nerve was not apparent under these 

 circumstances ; there was rather for the most part a gradual 

 sinking of excitability. It should also be noted that, with un- 

 altered position of electrodes, the closure of the ascending 

 current is first to become ineffective, so that at a certain stage 

 of dying the descending closure twitch is the sole effect of weak 

 currents. This fact agrees with the so-called Eitter-Valli law, 

 by which excitability is more quickly extinguished at points 

 nearer the centre than at the periphery. It would seem, how- 

 ever, as already pointed out, that the facts which support this 



