THE PHENOMENA OF CONDUCTION IN NERVE 



125 



it (at B). A pole changer is made use of so as to be able to divert the current in 

 the shortest possible time. Provided that the nerve has not been injured, the mus- 

 cle reacts when stimulated at either point. If carbon dioxid is now permitted to 

 flow into this chamber, the stimulation at A becomes ineffective, while that at B 

 persists. This procedure may be repeated a number of times, but the excitability 

 of the nerve returns very soon after the carbon dioxid hasbeen removed from the 

 chamber. It seems, therefore, that small quantities of this gas destroy the irrita- 

 bility of the nerve, but do not affect its conductivity, and hence, these two proper- 

 ties may be said to occur independently of one another. ^ If vapors of alcohol are 

 now introduced into this chamber, the nerve 

 loses even its conductivity, as is evinced by 

 the fact that the stimulation at B is now 

 quite ineffective. In a similar way, it may 

 be shown that ether and chloroform diminish 

 the irritability as well as the conductivity, 

 but the former more intensely than the 

 latter. Furthermore, it may be observed 

 that when the effect of these depressants 

 wears off, the conductivity is reestablished 

 more rapidly than the irritability. 



The Direction of Conduction. — 



In studying the different phenomena 

 connected with the conduction of nerve 

 impulses, it is customary to make 

 use of a musculomotor nerve which 

 is still attached to its muscle. Nerves 

 exhibit no visible signs of their ac- 

 tivity, i.e.f they do not liberate me- 

 chanical energy nor do they generate 

 heat or electricity in amounts suffi- 

 cient to be recognized by means of 

 our unaided sense-organs. In this 

 case, therefore, the muscle serves the 

 purpose of an indicator of the activity 

 of the nerve, because under normal 

 conditions every excitation of the latter gives rise to a muscular con- 

 traction. But naturally, before this effect can make itself felt, the wave 

 of excitation must have been transmitted from the seat of the stimula- 

 tion to the motor end-organ. Conduction, therefore, is the specific 

 function of nerve, its property of irritability enabling the stimulus to 

 produce certain chemico-physical changes which are then propagated 

 onward in the form of a wave of excitation or nerve impulse. It must 

 also be evident that any other motor mechanism or even a sensory 

 nerve, may be employed for these experiments. In the latter case, 

 however, it is necessary to arrange the sensory nerve in such a way 

 that it can give rise reflexly to a motor effect, because this is the most 

 convenient way of proving its activity. 



The preceding discussion pertaining .to the serial arrangement of 



^ Grunhagen, Pfluger's Archiv, vi, 1872, 181; and Luchsinger, ibid., xxiv, 1881, 

 347. 



Fig. 72. — Conductivity and 



TABILITY OF NeBVE. 



M, muscle; N, nerve; D, glass 

 chamber; C, Kipp apparatus; A and 

 B, electrodes inside and outside the 

 gas chamber. 



