456 ELECTRO-PHYSIOLOGY CHAP. 



even more apparent later on in preparations of Torpedo, in which 

 the homodromous current (of 30 Groves) was more than double 

 as strong as the heterodromous. A similar effect was seen still 

 more plainly on stimulating with induced currents, when the de- 

 pendence of the seeming irreciprocity of conduction upon current 

 density in the electrical organ was apparent. Du Bois- 

 Reymond " sent opening shocks from the sliding inductorium 

 (the primary coil being filled with rods), from surface to 

 surface of the skin in a preparation of Torpedo, which rested 

 between the clay shields of the leading-in vessels. The galvano- 

 meter was included in the same circuit." Each shock sent in by 

 opening the mercury key traversed the preparation alternately 

 in the homodromous and heterodromous directions. In the 

 following table RA stands for distance of coil, the figures 

 correspond with the deflections, reduced from 5000 turns at 

 2 mm. distance from the galvanometer mirror : 



RA= -^501 -|215 -f 5 l i 21 ^ ^453 ^215 ^477 

 RA = 10cm. ^25 ^28 ^27 -^28 -f 27 -f 27 



KA = 15cm. ^7^7^7^7 



RA= ^453 ^227 



Above a certain limit of current density the homodromous 

 current is thus much stronger than the heterodromous (^). 



It should not be unnoticed that, as has been said, " positive 

 polarisation " exhibits the same dependence upon the density of 

 the polarising (homodromous) current. Since it further shows 

 augmentation in proportion with the length of prismatic tract 

 between the leading-off clay points, and therewith the number 

 of polarised plates, the difference in intensity between homo- 

 dromous and heterodromous current is the more distinct accord- 

 ing as the distance between the leading-in electrodes on the 

 lateral surface of the organ-preparation is greater, so that we 

 may say that the apparent irreciprocity of conduction grows, like 

 positive polarisation, with the length of the prismatic tract 

 traversed. In this respect also it has been proved that the 

 ascendency of the homodromous current is much more pro- 

 nounced with induction shocks, or brief constant currents, 

 than with longer closures. Both manifestations are further 

 associated with vitality, and do not appear with sodden or 

 spontaneously defunct preparations, or with transverse passage 



