XI 



ELECTRICAL FISHES 451 



tive below, the abscissa. With homodromous currents (upper 

 series, with ascending arrow) the course of the curve above the 

 abscissa is absolutely and relatively positive ; below, it is absolutely 

 and relatively negative. With heterodromous currents (lower 

 series and descending arrow) the upper portion of the curve is 

 absolutely positive (relatively negative), the lower portion absolutely 

 negative (relatively positive). The resulting polarisation current 

 through the galvanometer is in each cut represented by the 

 shaded surfaces which comprise the curves resulting from algebraic 

 summation of the two polarisations with the axis of the co- 

 ordinates. It is obvious that the relatively negative polarisation 

 is equal in both currents, while the relatively positive polarisation, 

 on the other hand, is widely different (and with heterodromous 

 currents may fail altogether). Consequently the absolute posi- 

 tive polarisation (which with heterodromous currents is also 

 relatively negative) is unequal in fresh, excitable preparations 

 (i.) at the beginning of the experiment in the two cases. At a 

 subsequent stage this ratio of magnitude may be reversed (ii.) ; 

 the resulting homodromous polarisation finally becomes absolutely 

 (and relatively) negative, but is always smaller than the relatively 

 negative heterodromous polarisation (iii.) ; until finally there is 

 equal, relatively negative polarisation with both directions of 

 current (iv.). Sachs also saw stage iii. and du Bois-Eeymond iv. 

 on Malapterurus. 



The results of these experiments, as well as of those subse- 

 quently undertaken by Gotch (I.e.}, may be summarised by saying 

 that constant currents, of whatever strength and direction, if led 

 for a considerable time through an organ-preparation, invariably 

 yield relatively negative after-currents which are much stronger 

 with a homodromous than with a heterodromous direction of 

 the polarising current. Stronger homodromous currents, be- 

 ginning at a certain limen and lasting only a short time, yield 

 strong, absolutely and relatively positive after-currents, that sink 

 very gradually (du Bois-Eeymond's positive internal polarisation). 

 Heterodromous currents of equal strength and duration generally 

 yield weaker after-currents, relatively negative, absolutely positive 

 (du Bois-Eeymond's internal polarisation). 



As the strength of the relatively negative after -currents 

 (negative polarisation), which must be partly caused by physical 

 internal polarisation, depends in first degree upon the duration 



