584 THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



0'045 volt. 1 In regard to the physiological effects produced by the 

 electrical discharge of an entire fish, it must be remembered that the 

 small quantity, the rapid character of the development, and the sudden 

 cessation, causes the physiological effects of the high potential upon the 

 tissues of other animals to be of a different order to those produced by 

 a similar voltage of longer duration; and since the seat of electrical 

 production, the discs, is set in the moist tissues of the organ, only a 

 derivation of the currents produced by the electromotive changes will 

 pass through such external conductors as are supplied by the tissues of 

 any other animals which chance to be in the neighbourhood. 



Polarisation phenomena in electrical organs. The peculiar struc- 

 ture of the electrical organ must undoubtedly complicate the pro- 

 duction of such polarisation effects as are demonstrable in nerve, during 

 and after the passage of electrical currents. The main features of polar 

 changes in nerve are those associated with alterations in the excitability 

 and in the electromotive conditions of the tissue respectively. Evidence 

 of similar effects is not wanting in the case of electrical organs, but 

 this evidence can be only rendered intelligible after a brief considera- 

 tion of the polarisable media presented by such a series of com- 

 partments as exist in these structures. Each compartment has a 

 protoplasmic disc, with a dense array of nerves, both being polarisable 

 structures ; it is bounded on both sides by a more liquid mass, the 

 electrical conductivity of which is on a par with that of O6 per cent. 

 NaCl solution. 2 The disc thus offers to the passage of currents along 

 the column length a thin central plate of higher resistance, and when 

 non-polarisable electrodes are used for the passage of a current from 

 an external source through the length of a column, the polarisation 

 interfaces will obviously be situated on each surface of each disc. In a 

 column, therefore, there will be, as far as the discs and the contained 

 nerves are concerned, multiple anodes and cathodes, an anode and a 

 cathode being present in each disc. The polar changes in excit- 

 ability, if present, will thus resemble those produced when a current 

 is directed more or less transversely through a series of nerve fibres 

 lying side by side. We know that the more the direction of a 

 current is transverse in these latter structures, the less becomes its excit- 

 ing efficiency, and the less, therefore, any evidence of polar interference 

 with such excitability, in consequence of reversal of the direction of the 

 traversing current. We should not, therefore, expect, on a priori grounds, 

 any pronounced change in the response of an electrical organ, dependent 

 upon altered direction of a polarising current, when this is allowed to 

 traverse the plates in the direction of the columns. On the other hand, 

 if the polarising current is applied to the trunk of the electrical nerve, 

 then the nerve divisions in the plate will be the seat of extrapolar 

 changes, and the response of the organ should be affected in much the 

 same way as is that of a muscle under similar conditions. 



1 Recent observations by Gotch and Burch, made in 1899, have enabled an accurate 

 calculation of the electromotive force of the effect obtained from a strip of Malapterurvs 

 organ 15 mm. long. The electromotive force of the strip reached a maximum of 26 volts, 

 giving for the whole fish a maximum of 200 volts, and for each disc a maximum of 

 0'044 volt, since the strip contained 500 discs in series (Proc. Roy. Soc. London, 1899). 



2 Recent experiments on Malapterurus organ, made at Oxford, show that the resistance 

 for currents directed longitudinally through the columns is four times as great as that 

 offered to transverse currents. The greater resistance in the former case is an indication 

 of that of the discs. The resistance to transverse currents was found to be the same as 

 that of 0-6 per cent, NaCl. (Proc. Roy. Soc. London, 1899). 



