iv GENEKAL PHYSIOLOGY OF NEKVOUS SYSTEM 229 



tube which served as a gas chamber, and plugged the ends with 

 china clay saturated with isotonic salt solution. By using two pairs 

 of electrodes he was able to excite both the part of the nerve that 

 was being treated with C0 2 and the more proximal part outside 

 the gas chamber (A and B of Fig. 144). At a certain time after 

 passing the current of C0 2 into the gas chamber, stimulation of 

 the nerve at point A produced only a feeble response, which 

 gradually disappeared altogether; while stimulation at point B 

 was still fully effective. The impulse starting at B can therefore 

 be transmitted along the portion A of the nerve, in which excit- 

 ability has been depressed or abolished. This important experi- 

 ment is complementary to Waller's researches on the effects of 

 C0 2 on the electromotive response of nerve (Figs. 138, 139), and 

 proves that excitability and conductivity, while closely associated, 

 behave on artificial excitation as two distinct properties of the 

 nerve. 



Griinhagen's experiments were continued by Luchsinger, and 

 more particularly by Piotrowski, who extended them to anaes- 

 thetics, and endeavoured to differentiate the action of the latter 

 upon the excitability and the conductivity of nerve, by means 

 of various forms of electrical and mechanical stimuli. He con- 

 cluded as follows : 



(a) Carbon dioxide and carbon monoxide gases always produce 

 a marked depression of excitability in the intoxicated segment 

 without injuring conductivity. 



(6) Alcohol vapour causes an initial rise of both excitability 

 and conductivity : later on the second decreases more rapidly than 

 the first, until a stage is reached in which excitations aroused 

 above the intoxicated portion are no longer conducted, although 

 the nerve is still perfectly excitable at that point. 



(c) Ether and chloroform depress both excitability and con- 

 ductivity, but affect the former more rapidly and fundamentally 

 than the latter. Chloroform attacks the vitality of nerve more 

 powerfully than ether, so that its effects may become permanent. 

 Gotch also confirmed these results. 



(d} In all these experiments conductivity returns more rapidly 

 than excitability, when the action of these gases upon the nerve 

 is stopped. 



The results of these and many similar experiments are 

 obviously unsatisfactory, and are far from giving any clear idea of 

 the relations between excitability and conductivity in nerve. The 

 work in Verworn's laboratory of his pupil Fr. W. Frohlich (1903) 

 has thrown more light on this subject. Frohlich found that on 

 anaesthetising or asphyxiating a tag of nerve its excitability 

 diminishes gradually and almost evenly, while conductivity i.e. 

 excitability of the more central and uninjured parts of the nerve 

 is at first unaltered, and then, when the excitability has fallen to 



Q2 



