LI.] 



EXCITABILHT OF NERVE. 



257 



IM. 



be attached and through which vapours or gases can be passed, and 

 also with electrodes so that the nerve can be stimulated within or 

 outside the tube. Use a Pohl's commutator for this purpose. 



{h.) Pass CO^ from a Kipp's apparatus through the tube; on 

 stimulating the nerve at A 

 with repeated shocks, there is 

 no response, but on stimulating 

 at B there is. Find a strength 

 of stimulus which just excites 

 the nerve at A and B. On 

 passing COg A no longer re- 

 sponds to this stimulus, but 

 rerjuires a stronger stimulus, or 

 it may not respond at all. It 

 would s^fem that the excitatory 

 change set up at B is propagated 

 through A, although its excita- 

 bility is very feeble or nil. It 

 thus seems to conduct, even 

 though it is inexcitable. 



{('.) On passing the vapour of 

 alcohol the conductivity appears to vanish before the excitability. 

 It is better to suck the vapour through by means of an}'' form of 

 exhaust pump. The results, however, may be capable of a dififerent 

 interpretation. (Gad, Dm Bou-ReymoncVs ArcJiir, 1888, p. 395, 

 and 1889, p. 350; Piotrowski, " Trennung d. Peizbark. v. 

 Leitungsfah. d. Nerven," iUd.^ 1893, p. 205.) 



{d.) Cold. — Apply cold to a nerve as in 8, i.e., lay the nerve over 

 a glass tube through which cold water is conducted. Cold, like 

 CO.^, abolishes or diminishes the excitability, but not the con- 

 ductivity. 



The action of other substances, such as chloroform, ether, and 

 CO, have been investigated. 



Fig. 179 



Gninhagen's Experiment on 

 Conductivity v. Excitability. 



ADDITIONAL EXERCESES. 



8. Influence of Localised Cold upon Excitabili y (Grotch). 



A. Upon Nerve. 



The influence of changes in temperature upon excitability can be investi- 

 gated by arranging in the moist chamber a glass tube j)laced at right angles 

 to the nerve of a nerve-muscle preparation, and situated so that a small 

 portion of the nerve shall lie athwart the tube. Through the tube water at 

 temperatures varied at will from 10° to 30° C. is allowed to flow. 



The alteration in temperature causes a marked alteration in the electrical 



