THE FUNCTIONAL ACTIVITY OF THE ORGAN 



5 6 9 



the substance of the discs, flow through these from the nerve entry 

 layer to the opposite side. However, Pacini's generalisation obviously 

 breaks down since it is opposed to the condition of affairs in Malaj>- 

 terurus. 1 This will be rendered clear by the following table : — 



These and several other general characteristics of the activity of 

 electrical organs may be readily ascertained, by experiments upon living 

 specimens of fish when the specimen is placed in a suitable experimental 

 tank. In the case of the sluggish torpedo, the fish is allowed to rest 

 with the ventral surface upon a zinc plate, forming the floor of the tank, 

 whilst a second zinc plate is brought into contact with the dorsal 

 surface ; if both metallic contacts are connected by means of wires 

 with a suitable galvanometer, a forcible movement of the needle occurs 

 whenever the fish is aroused by mechanical means. The active Mala- 

 pterurus may be caught in an appropriate net, into which two sets of 

 wires have been woven, so that one shall be in contact with the cephalic 

 and the other with the caudal extremity. Finally, in the case of the 

 Gymnotus, it is sufficient to immerse two zinc plates or rods at each end 

 of a long narrow tank, along the floor of which the Gymnotus lies 

 extended. 



In this way it has been ascertained that, when the fish is aroused, 

 intense currents flow through its body, causing strong derivations to pass 

 through the surrounding water and along the wires connected with the 

 metallic contacts. 



If the ends of the wires are grasped by the hands, shocks are felt ; 

 if connected with a telephone, sounds are heard ; if connected with a 

 coil of wire surrounding a soft iron core, this is magnetised (hence an 

 electro-magnetic signal is effected) ; and if connected with liquid capable 

 of electrolysis, the products of chemical dissociation occur. It is difficult 

 to obtain from even a large torpedo any indication of an electrical 

 spark, for even when the external wires are separated by only *005 mm., 

 no such effect was observed by du Bois-Keymond ; but a small spark 

 has been seen on separating the external wires from contact with each 



1 The ending of the nerve in the caudal stalk of the disc of Malapterurus organ forbids 

 at present any generalisation from structure to function. The nerved part becomes in 

 Malapterurus galvanometrically positive to the unnerved, since the organ shock is from iiead 

 to tail ; it is thus the opposite of the condition in the other electrical fishes. A further 

 difficulty is raised by the localisation of the nerve-endings to the tip of the stalk, the large 

 expanded disc containing no nervous twigs. 





