580 COMPARATIVE HISTORICAL. 



special electrical organs (Rcdi, 1666), these animals can in part voluntarily (gymnotus and 

 malapterurus), and in part reflexly (torpedo), give a very powerful electrical shock. The 

 electrical organ consists of "compartments" of various forms, separated from each other by con- 

 nective-tissue, and filled with a jelly-like substance, which the nerves enter on one surface and 

 ramify to produce a plexus. From this plexus there proceed branches of the axial cylinder, 

 which end in a nucleated plate, the "electrical plate" {Billharz, M. Schulzc). When the 

 M electrical nerves " proceeding to the organ are stimulated, an electrical discharge is the result. 



In Gymnotus, the electrical organ consists of several rows of columns arranged along both 

 sides of the spinal column of the animal, under the skin as far as the tail. It receives on the 

 anterior surface several branches from the intercostal nerves. Besides this large organ there is 

 a smaller one lying on both sides above the anal fins. Here the plates are vertical, and the 

 direction of the electrical current in the fish is ascending, so that of course it is descending in 

 the surrounding water {Faraday, du Bois-Rcymond). 



In Malapterurus, the organ surrounds the body like a mantle, and receives only one nerve- 

 fibre (p. 529), whose axis cylinder arises near the medulla oblongata from one gigantic ganglionic 

 cell (Billharz), and is composed of protoplasmic processes (Fritsch). The plates are also vertical, 

 and receive their nerves from the posterior surface. The direction of the current is descending 

 in the fish during the discharge (du Bois-Rcymond). 



In the Torpedo, the organ lies immediately under the skin laterally on each side of the head, 

 reaching as far as the pectoral fins. It receives several nerves which arise from the lobus 

 clectricus, between the corpora quadrigemina and the medulla oblongata. The plates, which do 

 not increase in number with the growth of the animal (Delle Chiaje, Babuchin), lie horizontally, 

 while the nerve-fibres enter them on their dorsal surfaces, the current in the fish being from the 

 abdominal to the dorsal surface (Galvani). 



It is extremely probable that the electric organs are modified muscles, in which the nerve 

 terminations are highly developed, the electrical plates corresponding to the motorial end-plates 

 of the muscular fibres, the contractile substance having disappeared, so that during physiological 

 activity the chemical energy is changed into electricity alone, while there is no "work" done. 

 This view is supported by the observation of Babuchin, that during development the organs are 

 originally formed like muscles ; further, that the organs when at rest are neutral, but when 

 active or dead, acid ; and lastly, they contain a substance related to myosin which coagulates 

 after death ( 295 Wcyl). The organs manifest fatigue; they have a "latent period" 

 of '016 second, while one shock of the organ (comparable to the current in an active muscle) 

 lasts 0*07 second. About twenty-five of these shocks go to make a discharge, which lasts 

 about 0*23 second. The discharge, like tetanus, is a discontinuous process (Marey), 

 Mechanical, chemical, thermal, and electrical stimuli cause a discharge ; a single induction 

 shock is not effective (Sachs). During the electrical discharge the current traverses 

 the muscles of the animal itself; the latter contract in the torpedo, while they do not 

 do so in the gymnotus and malapterurus during the discharge (Steiner). A torpedo can 

 give about fifty shocks per minute ; it then becomes fatigued, and requires some time to 

 recover itself. It may only partially discharge its organ (Al. v. Humboldt, Sachs). Cooling 

 makes the organ less active, while heating it to 22 C. makes it more so. The organ becomes 

 tetanic with strychnin (Becqucrel), while curara paralyses it (Sachs). Stimulation of the 

 electrical organ of the torpedo causes a discharge (Matteucci) ; cold retards it, while section of 

 the electrical nerves paralyses the organ. The electrical fishes themselves are but slightly 

 affected by very strong induction shocks transmitted through the water in which they are 

 swimming (du Bois-Rcymond). The substance of the electrical organs is singly refractive ; 

 excised portions give a current during rest, which has the same direction as the shock ; tetanus 

 of the organ weakens the current (Sachs, du Bois-Reymond). Perhaps the electrical organs of 

 malapterurus is evolved from modified cutaneous glands (Fritsch). 



Historical. Richer (1672) made the first communication about the gymnotus. Walsh 

 (1772) made investigations on the torpedo, on its discharge, and its power of communicating a 

 shock. J. Davy magnetised particles of steel, caused a deflection of the magnetic needle, and 

 obtained electrolysis with the electrical discharge. Becquerel, Brechet, and Matteucci studied 

 the direction of the discharge. Al. v Humboldt described the habits and actions of the gym- 

 notus of South America. Hausen (1743) and de Sauvages (1744) supposed that electricity 

 was the active force in nerves. The actual investigations into animal electricity began with G. 

 Aloisio Galvani (1791), who observed that frogs' legs connected with an electrical machine con- 

 tracted, and also when they were touched with two different metals. He believed that nerves 

 and muscles generated electricity. Alessandro Volta ascribed the second experiment to the 

 electrical current produced by the contact of dissimilar metals, and therefore outside the tissues 

 of the frog. The contraction without metals described by Galvani was confirmed by Alex. v. 

 Humboldt (1798). Pfaff (1793) first observed the effect of the direction of the current upon the 

 contraction of a frog's leg obtained by stimulating its nerve. Bunzen made a galvanic pile of 

 frogs' legs. The whole subject entered on a new phase with the construction of the galvano- 

 meter and since the introduction of the classical methods devised bv du Bois-Reymond, i.e., 

 from 1 843 onwards. 



