246 



COMPARATIVE ELECTRO-PHYSIOLOGY 



Of great importance was the investigation carried 

 out by Du Bois-Reymond on the effects induced in the 

 electrical organ by the passage of currents in different 

 directions. Polarising-currents in the direction of the natural 

 discharge of the organ are distinguished, in the terminology 

 introduced by Du Bois-Reymond, as homodromous, and 

 those in the opposite as heterodromous. Polarisation-effects 

 in the direction of the natural discharge he distinguishes as 



' absolutely positive polarisation/ and 

 against that direction * as absolutely 

 negative.' A polarisation-current in 

 the same direction as the polarising- 

 current he calls ( relatively positive/ 

 and in the opposite direction 'rela- 

 tively negative' polarisation. It 

 was found by him that polarising- 

 currents of fair intensity and short 

 duration, whether homodromous or 

 heterodromous, would always give 

 rise to polarisation-currents in the 

 same direction as the natural dis- 

 charge. He believed this to be due 

 to the occurrence in the electrical 

 organ of two different polarisation- 

 Direction of responsive current effects, positive and negative. This 



will be understood from his own dia- 

 grammatic representation (fig. 157) 

 of the effect which he supposed to take place immediately 

 on the passage of the polarising-current. In the upper 

 figure the ascending arrow represents the homodromous 

 polarising-current This gives rise, according to Du Bois- 

 Reymond, to two opposite polarisation-effects. The de- 

 flection seen in the galvanometer is the resultant of these, 

 represented by the shaded part of the figure. The resultant 

 of a homodromous current, then, is positive polarisation, 

 both absolute and relative. The heterodromous current, on 

 the other hand, induces absolutely positive and relatively 



FIG. 156. Electrical Response 

 of Lamina QiNymphtta alba 

 due to Transmitted Excita- 

 tion from Petiole 



