88 Tait 



refractory period with strong excitations, that such coexistence is a general 

 phenomenon. As I have found exceptions to this rule, not only in nerve that 

 has been frozen and thawed again, but also in nerve which is recovering 

 from simple cold rigor, we are not at liberty to generalise and say that a 

 strong excitation in nerve is always accompanied by a longer refractory 

 period than a weak excitation. The exceptional behaviour in this regard 

 of nerve which has been frozen and then thawed would indicate that the 

 internal state of such nerve is not quite comparable with that of 

 anaesthetised nerve. 



If at any stage during the recovery of a nerve which has been frozen 

 and warmed again to room temperature, the nerve be once more frozen at 

 the same spot as before, freezing occurs this time without any twitching of 

 the muscle. The reason of this is clear when, instead of actually freezing 

 the recovering nerve, we simply lower its temperature a few degrees below 

 that of the room.^ Cold rigor then occurs at a temperature many degrees 

 above zero, although the nerve, previous to being frozen, ina,y have retained 

 its conductivity at all temperatures down to the freezing-point. Evidently, 

 therefore, a nerve which has been frozen, and subsequently thawed, is, for a 

 time at least, very susceptible to the influence of low temperature. 



This condition of the nerve, whereby it loses its conductivity so readily 

 with depression of temperature after having been once frozen and warmed 

 again to room temperature, is not limited to the first stages of recovery 

 after freezing. Long after the conductivity, as tested by rhythmical 

 stimulation at the fastest rate possible with the Kronecker apparatus, may 

 have to all appearance completely returned, the nerve still tends to go into 

 cold rigor at moderately high temperatures, though as time goes on this 

 tendency progressively diminishes. By testing the nerve in this way we 

 see that changes are produced by freezing which persist for a long time 

 after thawing. 



In showing such susceptibility to the depressing action of low tempera- 

 ture, thawed nerve does not stand alone. A similar condition is found in 

 nerve which, without being frozen, has been cooled to some temperature 

 sufficiently low to abolish its conductivity, and has then, during the stage 

 of recovery which ensues upon warming, been fatigued by rhythmical 

 stimulation.^ Furthermore, under certain nutritive conditions nerve may 

 normally, i.e. without any special experimental treatment, show a similar 

 extreme susceptibility to the action of slightly lowered temperature. The 

 temperature relations in regard to the conductivity of nerve under different 

 conditions have as yet been very imperfectly worked out. 



As was previously mentioned, the time for recovery of conductivity after 



1 By arranging that the freezing apparatus should fit on to the apparatus which I 

 used for simple cooling of nerve, it was possible, after freezing and then thawing a minute 

 portion of the nerve, to subsequently cool this portion to any desired temperature without 

 any shifting of electrodes. 



2 For details as to the method of treating the nerve, see paper previously referred to 

 on Fatigue of Medullated Nerve by the Method of Cooling (2). 



