Freezing of Nerve, with Special Reference to Fatigability 89 



freezing may be long. If the nerve be frozen twice at the same spot, the 

 time for recovery of conductivity after the second freezing is still further 

 prolonged, though full recovery of conduction, as far as it can be tested 

 with the most rapid rate of stimulation possible with the Kronecker 

 apparatus, does ultimately occur. Hitherto I have carried out no experi- 

 ments to test the effect of repeated freezings and thawings carried out on 

 the same nerve. Botanists have shown that plants subjected to repeated 

 freezings show gradual diminution in vitality with each freezing and 

 ultimately die. Arguing from the result of two freezings on nerve, it is at 

 least possible that freezing never occurs in excised nerve without some 

 slight irreparable alteration in its structure. 



To sum up at the present stage : — 



Nerve which has been frozen and thawed again is not, for 

 some time at least, in normal condition. After thawing, slow 

 changes begin to occur which ultimately lead to the more or 

 less complete restoration of its function. The time for such 

 restoration may vary greatly in different cases. As recovery 

 proceeds the nerve first of all becomes capable of transmitting 

 strong excitations; only at a later period is it able to transmit 

 weak excitations, and this improvement in functioning power 

 takes place gradually. Meantime, the refractory period becomes 

 progressively shorter and shorter. At any given stage the 

 refractory period corresponding to strong excitations may 

 apparently be shorter than that corresponding to weak; in 

 other cases again the reverse holds true, and the refractory 

 period for strong excitations is longer than that for weak. 



After a frozen nerve has been warmed to room temperature 

 and its conductivity is beginning to return, it may again cease 

 to conduct if simply lowered a few degrees in temperature. 

 By testing the nerve in this way for disappearance of con- 

 ductivity at different temperatures, it is found that a tendency 

 to cold rigor at relatively high temperatures persists for a con- 

 siderable time after freezing, though, as time goes on, this passes 

 off. In consequence of this exaggerated tendency to cold rigor, 

 a second freezing of the nerve following closely upon a first is 

 attended by no twitching of the attached muscle. 



On numerous occasions now I have observed that some time after 

 freezing, and especially after two acts of freezing, the muscle, which had 

 been lying quite still, would suddenly begin to move convulsively, or pass 

 into an irregular tetanus like a Hitter's tetanus. The result was in no way 

 due to drying either of the muscle or of the nerve, for care was taken 

 throughout to keep the preparation moistened with Ringer's solution ; 

 nor did any electrical stiunilation act on the preparation. That the source 

 of the disturbance lay in the previously frozen portion of nerve is indicated 

 by the fact that, on one occasion, when the muscle was thus in active 



