1905.] The Action of Anaesthetics on Living Tissues. 275 



Sei'ies V. 



The effect on the electrical resistance of the application of anaesthetic 

 vapours is of great importance in endeavouring to give an explanation of 

 the facts recorded above, and so, although the question has already been 

 studied by Waller,* I have performed a considerable number of experiments 

 in order to eliminate as far as possible the numerous sources of error present. 



The method finally adopted was to place the nerve on non-polarisable 

 electrodes in a chamber, pass in air saturated with water vapour, and take 

 several successive readings until either they remained constant or else the 

 rate of change was determined. Moist CHCI3 vapour was then admitted 

 for five minutes, a reading taken, the chamber washed out with moist 

 air for four minutes, and the final value observed. A linen thread wet 

 with M/10 NaCl solution rested on non-polarisable electrodes in the same 

 chamber, and readings of its resistance were taken alternately with the 

 nerve. A thermometer as close to the nerve and thread as possible gave 

 an approximation to the temperature ; as will be seen, the mean variation 

 of this is about 04° C, and in view of the difficulty of securing an equal 

 amount of moisture and an equality of salt content in the electrodes, threads 

 and nerves, the temperature error may for the present purpose be disregarded. 



Two methods of determining the resistance were used : — 



(1) The ordinary Wheatstone bridge, using non-polarisable electrodes and 

 a constant current from one Leclanche cell. 



(2) A slightly modified Kohlrausch apparatus, using the same electrodes 

 and alternate currents. 



With the control threads the results were identical ; both sets of readings 

 show a diminution of resistance of about 2 per cent, after CHCI3, in part due 

 to temperature alterations, in part to other causes. The nerves on the other 

 hand gave markedly different figures with the two methods. 



* Waller, ' Proc. Physiol. Soc., ; November 12, 1898 



