492 NERVE. 



The results were the same, whether the nerve stimulus was the induced 

 current, the galvanic current, the condenser discharge, or mechanical 

 compression ; in all cases C0 2 or CO caused a marked diminution of the 

 nerve excitability in the chamber, but had no such obvious effect upon 

 the conductivity of this portion of nerve ; on the cessation of the gas the 

 excitability was rapidly restored to its normal value. On the other hand, 

 alcohol vapour caused an initial increase in the local excitability and to 

 a less degree in conductivity ; this soon changed, the conductivity 

 becoming rapidly impaired before the local excitability diminished ; on 

 the cessation of the alcohol vapour the normal conductivity and excita- 

 bility were reinstated, but the latter returned quickly, the former much 

 more slowly. A stage in the alcohol treatment was always obtained in 

 which the excitation of the central end of the nerve was quite in- 

 effectual, whilst that of the altered nerve in the chamber was increased 

 in effectiveness. This result cannot be due simply to the fact that 

 propagation occurs along a considerable length of the affected nerve when 

 the excitation is central, but along a much smaller length when this 

 occurs in the gas chamber. It is not due to the spread of the vapour or 

 gas beyond the chamber to the central end, since simultaneous observa- 

 tion of the electrical change at this end shows that the central stimulus 

 is not influenced as to its exciting value by the play of the gas or vapour 

 on the more peripheral portion of the nerve. It must therefore be 

 concluded that C0 2 and CO are agents which influence local excitability 

 more than conductivity, whilst alcohol influences conductivity more than 

 local excitability. The distinction between the effects of C0 2 and alcohol 

 as regards conductivity is further demonstrated by determining the 

 rate of propagation from the central excitation to the motorial nerve- 

 endings. C0 2 and CO have but little influence upon this, whereas 

 alcohol vapour causes a retardation from 28 to 4 metres per second. 



Ether and chloroform act by diminishing both local excitability and 

 conductivity ; the former, however, is diminished much earlier and in a 

 more pronounced manner than the latter. Thus, in one of the writer's 

 experiments, ether vapour for thirty seconds produced a fall of local 

 excitability such that the stimulus (break induction current) became 

 quite inadequate, whilst conductivity, as tested by a similar central 

 stimulus, was unimpaired. "When the vapour was allowed to act for 

 two minutes, the excitability was very much diminished, but still longer 

 exposure was necessary to produce impairment of conductivity. On the 

 Cessation of the ether, the central excitation became again adequate in 

 two minutes, showing the return of conductivity, whilst the local ex- 

 citability did not reappear until fifteen minutes had elapsed, and even 

 then was not restored completely for another ten minutes. Chloroform 

 is far more toxic than ether ; it produces the same effects, but is apt to 

 permanently injure the nerve. 



To the above experiments with ether, obtained under the direction 

 of the present writer, may be added some with C0 2 . These show 

 that it is always possible to abolish conductivity by this gas, but that 

 excitability is invariably affected first, and the subsequent impairment 

 of conductivity occurs only when the action of C0 2 is prolonged. Just 

 as with ether, recovery takes place rapidly as regards conductivity, and 

 far more slowly as regards excitability. Similar experiments with 

 nitrous oxide showed no anaesthesia as affecting either nerve function ; 

 the local excitability seemed to be always slightly augmented by the 



