62 ELECTRO-PHYSIOLOGY CHAP. 



very remarkable, and of great theoretical interest. We found 

 (vol. i. pp. 359, 450), in considering the effect of ether on muscle, 

 that conductivity is first abolished, next contractility, and last of 

 all local excitability. This last is still expressed in certain 

 secondary electromotive phenomena (including the positive 

 polarisation current), and in the demarcation current, at a time 

 when contractility is already abolished. In nerve also, conduc- 

 tivity appears to surfer in first degree from the action of ether, 

 chloroform, alcohol, etc., as appears directly from the persistence of 

 the nerve-current with abolished conductivity (if this be accepted 

 in the sense laid down above as the expression of persistent 

 local excitation). By using a method first applied by Griinhagen 

 (20), the conductivity of nerve may easily be abolished locally 

 if the narcosis is confined to the lower end of an exposed frog's 

 sciatic, by drawing the nerve through a glass tube which leaves 

 the central end free, and is itself closed at both ends save for a 

 small opening for the passage of the nerve. Three other glass tubes 

 are fused into the wall of this tube ; two serve to lead in the 

 gases or vapours, the third is for the electrodes ; the middle 

 portion of the nerve rests upon the electrodes. There will then 

 invariably be a stage of narcosis, in which the strongest excitation 

 above the narcotised tract is ineffective, while a much weaker 

 stimulus still excites below (i.e. in the tube). Eventually, of 

 course, this part is also anaesthetised. If air is passed through 

 the tube the normal condition will be reinstated. Under these 

 circumstances, therefore, the conductivity of the nerve is ex- 

 tinguished, while local excitability is maintained, and even at 

 first augmented, in the narcotised tract a state which we found 

 to be the rule in muscle under similar conditions (supra). In 

 these experiments again, as pointed out by Pereles and Sachs 

 (21), there are perceptible differences between the centripetal and 

 centrifugal fibres of a mixed nerve (sciatic). If the minimal 

 stimulus, which discharges a movement of the foot, is first deter- 

 mined above the central tract that is to be narcotised, along with 

 the strength of stimulus necessary to produce a reflex movement 

 of the leg from the web of the foot, the inevitable consequence 

 of narcosis is the earlier disappearance of reflex than of direct 

 movements. The same result follows even more infallibly 

 from analogous experiments in which the nerve-trunk is excited 

 by tetanising, now above and now below the etherised tract. 



