440 ELECTRO-PHYSIOLOGY CHAP. 



self-excitation of the organ, by its own discharge, is not merely 

 possible but the rule. Gotch refers the multiple apices of the 

 curve of discharge (supra), 011 stimulating with single induction 

 shocks, principally to a second set of discharges excited from 

 other prisms by the current of those first discharged by the 

 impulse from the nerve, so that the later discharges are in a 

 sense analogous with secondary contraction. Schonlein urges 

 against this view that oscillating discharges might then be 

 expected with brief closures of the battery current, which is not 

 the case. 



V. IMMUNITY OF ELECTKICAL FISHES TO THEIK OWN 



DISCHARGE 



It is in the last degree surprising, in view of the intensity 

 of physiological action in the discharge of electrical fishes, that 

 the most powerful shocks, which at once kill fish or other animals 

 within reach, should apparently not have the smallest effect upon 

 the generators of these electrical batteries, although " the body 

 of an electrical fish is better fitted to receive the shock of its own 

 organs than the body of any other animal " (du Bois-Reymond). 



Humboldt made experiments on Gymnolus which show the 

 insensibility of the animal to the most powerful shocks from its 

 own kind. He chose out one strong and two very weak gymnoti, 

 placing them so that the weak fish led the discharge from the 

 vigorous animal into his own body. The two weak fish were 

 totally unaffected. He suggested that the skin might be a pro- 

 tection against the electrical current, and this opinion was widely 

 held before the publication of du Bois-Eeymond's " preliminary 

 sketch." Du Bois showed first in Malapterurus that two wires 

 insulated down to the ends, and introduced into mouth and gut, 

 received the discharge in any position, and led it off externally 

 in accordance with the received theories, thus proving that the 

 shock really passes through the body of the fish, though, strangely 

 enough, the point was again disputed by de Sanctis in 187-J. 

 Mcdapterurus, moreover, proves to be as insensible to other electrical 

 shocks as to its own. " The alternating currents of an induc- 

 torium, which soon killed the fresh-water fish in the trough, were 

 hardly detected by Malapterurus. It only pointed its barbels 

 backwards, and placed itself with its body vertical to the least 



