THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 247 



negative polarisation, According to Du Bois-Reymond, 

 further, heterodromous shocks induce no relatively positive 

 polarisation, or only infinitely little (see down curve in lower 

 part of figure). On sending congruent alternating currents 

 from Saxton's machine, he ^ 



obtained only the absolutely 

 positive polarisation - effect. 

 This he accounted for by 

 supposing the relatively nega- 

 tive polarisations in both 

 directions to cancel each 

 other ; the heterodromous 

 positive to be so small as 

 to be practically negligible ; 

 and the homodromous posi- 

 tive therefore to be alone 

 effective. 



Du Bois-Reymond failed 

 to recognise the element of 

 excitation in these phe- 

 nomena. What he calls 

 positive polarisation has been 

 shown by subsequent workers 

 to be due to local polar ex- 

 citation. But the question 

 as to how polarising-currents 

 in both directions could give 

 rise to a single-directioned 

 responsive effect has not up 

 to the present, so far as I am 

 aware, been explained fully 



FIG. 157. Diagrammatic Representa- 

 tion by Du Bois-Reymond for Ex- 

 planation of Electrical Response in 

 Organ of Torpedo. 



The natural discharge is here supposed 

 to be from below to above. A 

 homodromous current \ (upper half 

 of figure) is supposed to induce 

 two opposite polarisations, positive 

 and negative. The resultant, repre- 

 sented by shading in figure, is 

 absolutely and relatively positive. 

 A heterodromous current \ , on the 

 other hand, is regarded as inducing 

 a resultant absolutely positive and 

 relatively negative polarisation 

 (lower part of figure). 



and satisfactorily. The ex- 

 periments carried out on leaves, which I am about to 

 describe, will, however, throw much light on this subject. 



It has already been shown, from anatomico-physiological 

 considerations, that there are certain leaves which approxi- 

 mate to the character of single plates of such electrical organs 



