viii CONDUCTIVITY AND EXCITABILITY OF NERVE . 63 



Here, too, the disturbance of the body caused by the centripetal 

 conduction of a sensory excitation, on stimulating the lower point, 

 is the first to die away, while movements of the foot can still be 

 excited from above, although the stimulus which produces them 

 is weaker than the other. " In local narcosis of the frog's sciatic, 

 conductivity is first abolished in the sensory, and later in the 

 motor nerve-fibres. On recovery from narcosis, the motor fibres 

 sooner become capable of conducting than the sensory fibres." 



More exact investigation shows that the ratio between con- 

 ductivity and excitation in nerve may alter in quite another sense. 

 Grunhagen (I.e.) observed, at a certain stage of C0 2 narcosis, that 

 the local excitability of a (peripheral) tract of nerve may be 

 considerably depressed, while the effect of stimulating the un- 

 poisoned part of the nerve is unaltered, although the excitation 

 process there discharged must be transmitted through the 

 narcotised area. Similar experiments were carried out later by 

 Szpilmann and Luchsinger, Hirschberg, Efron, Gad and Sawyer, 

 Goldscheider, and lately in detail by Piotrowsky (22). From 

 these the very significant fact appeared, that with local application 

 of alcohol vapour, ether, or chloroform, conductivity was as a rule 

 first and most fundamentally affected at such parts of the nerve, before 

 excitability underwent any perceptible diminution. With C0 2 , 

 on the contrary, as well as CO, conductivity is quite unaffected, 

 while local excitability is quickly abolished. These observations 

 are the more striking because they seem to contradict the current 

 opinion that excitability and conductivity are in the same ratio, 

 i.e. that when one declines the other sinks, and vice versa. Yet 

 we must admit the double capacity of nerve-fibres, on the one 

 hand to conduct excitation, on the other to be thrown into 

 excitation at any point of their course by external factors 

 (stimuli), to be but different expressions of the same fundamental 

 property of nerve-substance, and consequently inseparable. The 

 most natural conclusion from this is, in the language of Hermann, 

 that the excitatory process repeats itself constantly during con- 

 duction that each particle of the nerve falls into the same state, 

 whether it is affected by the impulse running along the nerve, 

 or is directly excited by an external stimulus, so that the process 

 of conductivity is first initiated in it. 



From this point of view conductivity in nerve is, like every 

 conductive process within an excitable substance, no more than 



