Freezing of Nerve, with Special Reference to Fatigability 87 



stimulated before freezing, during the frozen condition and after thawing. 

 For all we know, any one of these factors may influence the result, and 

 although I have carried out experiments to determine the possible influence of 

 various of them, I have as yet reached no positive conclusion. 



It must not be assumed that in every case recovery of the nerv^e occurs 

 after freezing. In a certain small number of cases in my experiments the 

 nerve did not recover even after a prolonged rest. In each of these cases, 

 however, there was reason to believe that the nerve before b^ing frozen 

 was not in a normally healthy condition, so that we may look on death of 

 the nerve from freezing as quite an unusual phenomenon. 



No matter whether the return of conductivity after thawing be rapid 

 or delayed, it is always possible to detect stages in the re-establishment of 

 full conduction. As recovery occurs the nerve first of all regains the power 

 of transmitting strong excitations ; only at a later period is it able to conduct 

 weak excitations, and in a case where recovery takes place slowly the 

 gradual improvement of the nerve in the transmission of successively 

 weaker and weaker excitations is easily followed. Such observations may 

 be made by using single-break shocks of different intensity to excite the 

 nerve. 



When one uses, on the other hand, series of rhythmical stimuli of 

 varying rate so as to examine the duration of the refractory period, one 

 finds that at first single initial twitches are got even with low rates of 

 stimulation, at a later stage tetanus; only after some time does tetanus 

 occur on rapid stimulation, but eventually even with the most rapid rates 

 at one's command the muscle is always thrown into tetanus. This points 

 to a gradual and progressive shortening of the refractory period throughout 

 the stage of recovery. 



As regards the duration of the refractory period corresponding to stimuli 

 of different intensities, the result seems to fall out in two different ways 

 according to circumstances. As a rule it is found that the refractory 

 period corresponding to a strong excitation is shorter than that correspond- 

 ing to a weak one. This is indicated by the fact that rhythmical stimulation 

 of high intensity tends to produce full tetanus of the muscle at a time when 

 stimulation at the same rate but of lower intensity causes only an initial 

 twitch. In a minority of cases an opposite effect is got, viz. full tetani 

 occur on weak stimulation, while initial twitches follow on strong 

 stimulation, pointing to the fact that in these cases the refractory period 

 is shorter for weak stimulations than for strong. The conditions determin- 

 ing which of these two effects should follow I have been unable to discover. 



The fact that, under the special conditions of freezing followed by 

 thawing, the refractory period of nerve may apparently be shorter thf 

 more intense the preceding excitation, is worthy of special attention. 

 Frohlich, who first systematically investigated changes in the refractory 

 period of nerve by means of the method of rapid rhythmical stimulation (10), 

 was inclined to conclude, from the coexistence in ana3sthetised ner^•e of long 



