1896.] 



Observations on Isolated Nerve. 



309 



nerve effected by weak tetanisation at the two exciting electrodes 

 e, e, but principally affecting a less disturbed portion L, undergoes a 

 negative variation (du Bois-Reymond), the magnitude of which is 

 taken as the index to the magnitude of chemico-physical change 

 aroused in the nerve under various chemical conditions. 



Care is observed to avoid the ordinary fallacies, and to obtain 

 a " negative variation " as far as possible clear of electrotonic 

 effects. Action-currents (significant of physiological effects in nerve) 

 are distinguished from physical effects by means of anaesthetics, 

 C0 2 ,Et,0,CHCl 3 * 



The physiological state of the nerve is tested by tetanising currents 

 of low and uniform intensity, of uniform duration (7^ and later 15 

 seconds), at uniform intervals (1 minute), in both directions. The 

 series of negative variations or action currents led off to the galva- 

 nometer, gives a corresponding series of deflections which are regis- 

 tered on a slowly descending photographic plate. 



The plan of procedure adopted throughout has been to take for a 

 period a normal series of deflections, then to submit the nerve to 

 the action of a reagent (without removal from the electrodes in the 

 case of gases, but with such removal in the case of solutions), finally 

 to take for a further period the series of increasing or decreasing 

 or reversed deflections of the chemically modified nerve. Altera- 

 tions of resistance were controlled by aid of a standard deflection of 

 0*001, volt let into the nerve and galvanometer circuit at beginning 

 and end of experiment. 



The results so far acquired may be considered under the following 

 heads : — 



1. The effects of anaesthetics, and of some gases. 



2. The effects of several chemical substances in solution. 



3. The effect of carbon dioxide. 



4. Theoretical considerations 



1. Anaesthetic vapours were employed at the outset of these ob- 

 servations with a view of distinguishing between physiological and 

 physical effects. Their action was subsequently studied in detail, 

 more especially as regards the comparison between ether and chloro- 

 form (and other chloromethanes and chloroethanes) upon living 

 matter as represented by nerve. f 



Ether vapour (Et 2 ; also EtCl, EtBr, and EtI) produces a more 

 or less prolonged abolition followed by complete recovery of excit- 

 ability. 



Chloroform vapour (CHC1 3 ; also other chloromethanes and chloro- 

 ethanes) produces still more prolonged and frequently final aboli- 

 tion. 



* 1 Physiol. Soc. Proc.,' February, 1896. 

 t ' Physiol. Soc. Proc.,' "November, 1895. 



