92 Tait 



Throughout this experiment the drum was kept uniformly revolving, 

 and the figure shows a record of eight minutes' duration. 



As to the internal processes in the nerve corresponding to the kind of 

 tetanus seen in tracing 3, all we can say is that the nerve readily transmits 

 at least the first excitation of the series, but this preliminary effort is 

 followed by temporary disablement which, as the stimulation proceeds, is 

 gradually'' recovered from. That the preliminary twitch in the tetanus 

 represents only one excitation is probable from its correspondence in height 

 with the twitches seen in tracing 5, which, from other experiments, we 

 know to correspond to one excitation alone. But why the first excitation 

 of the series is followed by a temporary fall in conductivity while later 

 excitations are not, is hard to say. 



III. Nerve Fatigue after Freezing. 



In a previous paper (2) I have shown that, after being in cold rigor, 

 nerve may be readily fatigued during the stage of recovery of conduction 

 due to subsequent warming, and that the fatigue then induced may be 

 more or less long-lasting. The method adopted to produde such fatigue 

 was sometimes by means of alternate central and peripheral rhythmical 

 stimulation, sometimes by means of central stimulation alone. As some- 

 what similar results have been obtained after freezing of the nerve, I shall 

 now describe them. 



(a) Short-lived Fatigue. 



On p. 87 it was pointed out that, during the recovery stage after 

 freezing, the refractory period corresponding to different intensities of 

 stimulation may sometimes be shortest when the intensity is greatest, 

 while in other cases again the reverse is the case. It would follow from 

 this that in certain cases during recovery the refractory period may be 

 almost the same for all intensities of stimulation. The example shown in 

 fig. 3 is apparently a case in point. 



In the experiment of which this is a record, a minute portion of the 

 nerve was frozen and the conductivity found to remain absent for some 

 considerable time after thawing. The nerve was taken off the electrodes 

 and put back into Ringer's solution for an hour and a half. At the end of 

 that time it was found to have almost entirely regained its conductivity, 

 the tetani on central stimulation being practically as high as those obtained 

 on peripheral stimulation. The previously frozen part of the nerve was 

 now gradually cooled to —1° C, at which temperature cold rigor came on. 

 On gradually warming the nerve again conductivity returned, at first 

 imperfectly and then more and more completely. At a temperature of 

 -l-3"5° C. isolated make-and-break shocks at intensity 200 are seen to 

 produce single twitches, while rhythmical stimulation at a rate of 144 per 

 second produces " fatigue tetani " both at 200 and at 500 units of intensity. 



