570 THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



other just as the organ discharges. The explanation of this is related 

 to the character and situation of the organ in the fish. This is itself 

 a moist conductor, surrounded by other moist tissues, which afford a 

 perpetual short circuit for any current flow which is caused by electro- 

 motive changes in the organ discs. It is impossible, therefore, to com- 

 pletely open the circuit, for the separation of the external wires merely 

 opens one of the derivation circuits. 1 



The short circuit afforded by the body and surroundings of the fish 

 inclined the early physicists to dispute the possibility of an external 

 derivation being adequate for the production of the shock-effect on 

 man ; but Cavendish demonstrated that shocks similar to those given 

 by Torpedo could be easily obtained from a model containing an electro- 

 motive source, when immersed, like the fish-organ, in moist sur- 

 roundings. 2 



It is obvious that the intense electrical currents produced by 

 the simultaneous activity of the discs in G-ymnotus, Malapterurus, or 

 Torpedo traverse the columns, and that the lines of current-flow must 

 comprise the moist-conducting tissues of the body of the fish. These 

 tissues are not only such excitable tissues as muscle and nerve, but the 

 central nervous system itself. In the case of the G-ymnotus, the head 

 forms, as it were, one terminal of the system of powerful batteries 

 constituted by the functional activity of the very extensive organs, yet 

 although an extremely intense current must traverse the brain of this 

 creature, the vitality of the tissue is not impaired. The excitable 

 structures of such electrical fish as G-ymnotus, Torpedo, and Malapterurus 

 thus appear to have become relatively immune to the passage of intense 

 electrical currents. 



The simultaneous development of electromotive changes in all the 

 discs causes each column to be transformed into a series of batteries, 

 coupled up in series for intensity, and when, as in the organ of G-ymnotus 

 and Malapterurus, the series of discs is a very extensive one, the arrange- 

 ment is one eminently adapted for a circuit comprising a large external 

 resistance. Such a resistance is offered by the fresh water in which 

 these fishes live. On the other hand, groups of shorter columns, stacked 

 side by side, afford an arrangement like that produced by coupling up 

 batteries in parallel series, and adapted for a circuit which comprises 

 a low external resistance. This is more or less the case in the organ of 

 Torpedo, in which the columns are comparatively short, but so arranged 

 that from 400 to 1000 are placed side by side in each organ ; in this 

 connection, du Bois-Eeymond pointed out that the electrical resistance 

 of sea water is one million times less than that of fresh water. 3 



As to the releasing cause of the activity of an electrical organ in the 

 entire fish, it is undoubtedly a central nervous discharge, the excitatory 

 state reaching the organ through the electrical nerves ; but, like 

 that of muscle, the activity can be evoked either reflexly in the 

 entire fish, or in separated masses of the organ by excitation of the 

 entering nerves. 



A mass of electrical organ, when removed with its attached nerves 

 from a recently killed fish, thus resembles a muscle nerve preparation, 

 inasmuch as it affords opportunities for the study of the response of a 



1 du Bois-Reymond, Sitzungsb. d. k. preuss. Akad., d. Wissensch., Berlin, 1883, 1885. 



2 Cavendish, Phil. Trans., London, 1776, vol. Ixvi. pt. 1. 



3 du Bois-Reymond, loc. cit. 



