Freezing of Nerve, with Special Reference to Fatigability 85 



The next stimulation also evokes tetanus, but of a less height. Immediately 

 thereafter the muscle goes into freezing tetanus. When next tested, con- 

 ductivity is seen to be abolished. This is a case in which, by an accident, 

 the temperature of cold rigor corresponding to the definite length of nerve 

 cooled and the freezing-point of the nerve coincide, and the immediate 

 improvement in conductivity just before freezing sets in is well shown. 

 Similar tracings, none of them, however, so strikingly illustrative as this 

 one, might be repeated indefinitely. 



Once or twice it was noted that mere stimulation of the nerve, when 

 the temperature was very low, sufficed to send the muscle at once into a 

 tetanic contraction as if over-cooling had occurred and the molecular com- 

 motion due to stimulation had suddenly induced freezing : but such cases 

 are rare. 



During the process of freezing the conductivity is not necessarily at 

 once abolished. After the muscle has begun to twitch convulsively, 

 rhythmical stimulation of the central end of the nerve may produce a 

 smooth and elevated tetanus which stands up above the irregular twitches 

 immediately preceding it, and corresponds exactly in duration to the 

 period of stimulation on the cessation of which the irregular twitching 

 begins again. If the freezing be interrupted during this stage, the conduc- 

 tivity is not necessarily abolished. Further, even after the muscle twitch- 

 ings due to the occurrence of freezing have entirely ceased, the property of 

 conductivity may still be retained by the frozen portion. The muscle 

 may react by single twitches to isolated shocks, and to rapid rhythmical 

 stimulation applied centrally ; but these twitches quickly fall off in height 

 and the frozen portion soon ceases to conduct. Hitherto I have not ob- 

 served tetanus of the muscle to follow upon rapid rhythmical stimulation 

 under these conditions. 



To sum up: — When freezing takes place the nerve first becomes 

 white externally. About the same time an improvement in con- 

 ductivity suddenly occurs: excitatory processes are not so much 

 cut down in amplitude on passing through the cold area and 

 the refractory period becomes shorter. 



Immediately thereafter, in consequence of the molecular dis- 

 turbance due to freezing, the whole nerve is, as a rule, thrown 

 into excitation. In cases, however, where the temperature of 

 cold rigor is normally high, the disturbance arising at the site of 

 freezing is not propagated outwards because of the existence 

 of cold rigor in immediately adjoining parts of the nerve. 



When the nerve is in this state of more or less tumultuous 

 agitation due to the occurrence of local freezing, it may retain 

 for some time the property of conducting rhythmical stimuli 

 of external origin throughout its whole length, including the 

 actual site of freezing. Conductivity, finall}', becomes abolished 

 if the nerve be sufficiently cooled, though often enough it does 



