90 Tait 



contraction, the tetanus ceased at once when the nerve was snipped across 

 with scissors just peripheral to the site of freezing. It would consequently 

 seem that, under certain conditions, after freezing the nerve is in a state of 

 highly unstable equilibrium and may easily pass into a state of violent 

 commotion. On one occasion at least, after such a violent disturbance had 

 occurred in the preparation, the conductivity of the portion of nerve affected 

 by freezing was found to remain permanently absent although the muscle 

 still responded to peripheral stimulation of the nerve. 



One further phenomenon requires to be mentioned. When the nerve, 

 after being thawed, has recovered to such an extent that tetani of the 

 muscle follow on rapid stimulation, these tetani often tend to take at 

 first a peculiar form. This is illustrated in fig. 2. (Although the figure 

 illustrates more than the point immediately in question, a complete ex- 

 periment has been shown, partly because it happens to demonstrate in 

 small compass a number of points already described, partly because the 

 conditions under which this peculiar form of tetanus is got are thereby 

 rendered more clear.) 



The tracing marked 1 shows the condition of the conductivity at the 

 commencement of the experiment, the whole preparation being at room 

 temperature. The muscle tetani corresponding to rhythmical stimulation 

 (rate 144 per second) are smooth and elevated : in other words they are 

 normal tetani. Tracing 2 shows a freezing tetanus followed by ultimate 

 loss of conductivity. The nerve was then warmed by turning on fluid at 

 room temperature at the spot marked " hot." Tracing 3, which illustrates 

 the point immediately under discussion, shows a progressive and rapid 

 return of conductivity, rhythmical stimulation at the same original rate 

 (144 per second) being used throughout to test the condition of the nerve. 

 The first three muscle responses are practically single twitches, the nerve 

 being stimulated at intensities 30, 100, and 300, respectively. The next 

 three are examples of the peculiar form of tetanus in question. In each of 

 these the muscle first gives a single twitch and immediately thereafter 

 relaxes. Then it begins to contract again, not in the rapidly summated 

 fashion of the tetani in tracing 1, but more deliberately and slowly. With 

 each successive series of stimulations the relaxation of the muscle after the 

 preliminary twitch becomes less marked ; this change is due, as other 

 experiments have shown, to the rapid recovery going on in the nerve. 

 Further, the preliminary twitches all show a certain regularity in height, 

 thus indicating that the corresponding nerve processes are somewhat 

 similar and of approximately the same magnitude. 



A little later the tetani following rhythmical stimulation are free from 

 irregularities (tracing 4), though the tetani are not so high as in tracing 1. 

 The cold fluid was now made to run slowly through so as to cool the 

 nerve gradually, and as a result the muscle responses become single initial 

 twitches of approximately the same height as the preliminary twitches in 

 tracing 3. These finally become abolished, and the nerve freezes again 



