80 



ON THE INTERNAL POLARISATION OF NERVES. 



arm t 2 of the Morse, the contact t^-a is broken. The two con- 

 tacts are carefully insulated by a plate of ebonite I4 mm thick. The 

 base-plate of the Morse key is cut in two, and a is isolated from b 

 by a layer of pitch. In the diagram the continuous lines and 

 arrows indicate the path and direction of the polarising current ; 



Fig. 3. 



the dotted lines and arrows show the path and direction of the 

 current going to the galvanometer. 



There is therefore no possibility of the polarising current break- 

 ing into the circuit of the galvanometer. Du Bois-B/eymond found, 

 however, that such an insulation is not sufficient when strong 

 currents are employed, inasmuch as, in spite of it, especially if the 

 atmosphere is moist, there may be a slight escape of the polarising 

 current to the galvanometer 1 . This drawback, however, did not in- 

 terfere with the investigation. In the first place I used only pretty 

 weak currents ; the strongest being produced by 3 Meidinger's 

 elements with 20,000 units in the rheochord. In the second place I 

 was favoured in my work by dry weather, in consequence of which, 

 for a long time, no action on the galvanometer from this source 

 of error could be perceived. Even when the atmosphere became 

 more highly charged with moisture and in consequence my gal- 



1 Du Bois-Reymond, Untersuchungen iiber thierische Elektricitat, ii. Th. 

 p. 496, 1848. 



Abth. 



