ELECTROTONUS 561 



the external galvanometric circuit, as indicated by the dotted 

 arrow. 1 



In the medullated animal nerve, the electrotonic currents 

 increase with the intensity of the polarising current. In the 

 vegetal nerve, I have obtained exactly similar results. 

 Taking a fresh and vigorous specimen, the polarising elec- 

 trodes were placed at a distance of 2*5 cm. from each other, 

 the pair of extra-polar electrodes, where the electrotonic 

 effects are observed, being separated from these by 2 cm. and 

 divided from each other by 2 cm. also. The value of the 

 acting polarising E.M.F. could be varied by the use of a 



-2 



M 



FIG. 338. Extra-polar Electrotonic Effects under an Acting E.M.F. 

 which rises from -6 to I -4 Volts 



A, an-electrotonic deflections seen to left ; K, kat-electrotonic to right. 



potentiometer arrangement. In order to induce in the extra- 

 polar electrodes, an-electrotonic and kat-electrotonic effects 

 alternately, the current in the polarising circuit can be sent 

 in one direction or the other by means of a reversing-key. 

 The record of the galvanometer deflection, in the extra-polar 

 circuit, gives a measure of the electrotonic effect induced. 

 In fig. 338 is seen such a record of effects both an-electro- 

 tonic and kat-electrotonic, taken while the acting E.M.F. was 

 increased from '6 to 1-4 volt, by steps of '2 volt at a time. 



1 Certain considerations, which need only be referred to here, cast some 

 doubt on the validity of this assumption. But as it is so widely current in 

 physiological literature, I shall confine myself, in dealing with the subject of the 

 electrotonic current and its variations, to those indications in the external circuit 

 which are afforded by the galvanometer. 



O O 



