xi ELECTRICAL FISHES 407 



the two electrical nerve-fibres (Bilharz). This spot is distinguished 

 from the surrounding matter of the cord by its darker colour, and 

 is found under the microscope to be a multipolar ganglionic body 

 of giant dimensions, its axis-cylinder process forming an electrical 

 nerve. The two ganglionic bodies (Fig. 265) are lenticular in 

 form, the equatorial diameter being as much as 0'21 mm., the 

 axial about one-half this. Internally there is a large blistered 

 nucleus, which, like the cell itself, is ellipsoid. ' " The body of the 

 cell is never rounded towards its neighbours, but lengthens gradu- 

 ally into large protoplasmic processes, which subsequently curve 

 distinctly, and form a loose tissue at about the middle diameter of 

 the cell." This becomes more dense after the axis-cylinder process 

 has been given off, and forms a kind of sieve (base of the electrical 

 nerve), from which the nerve emerges, and becomes invested on the 

 other side with the medulla. This structure is the more remark- 

 able since the protoplasmic processes, as well as the axis-cylinder 

 developed from them, are certainly of nervous 'origin. 



II. GENERAL ACTION OF DISCHARGE FROM ELECTRICAL FISHES 



The physiological action of the shock is, of course, of first 

 interest, in so far, at least, as concerns the powerful discharges 

 from the highly differentiated electrical organs of Torpedo, 

 Gijmnotus, and Malapterurus. The subjective physiological action 

 of the shock of the fish may, as was pointed out by du Bois- 

 Eeymond, take effect under different conditions. It is, however, 

 indispensable (since all action of an animal or vegetable electro- 

 motor is produced by short-circuiting) that the curves of current 

 should impinge upon the human body at sufficient density, either 

 directly, or by means of a conductor of resistance parallel with 

 that of the organic tissues, e.g. water, moist non-conductors, 

 etc. Metal, employed as the intermediate layer seeing that its 

 resistance vanishes against that of the moist parts is a protection 

 against current-diffusion, according to Kirchhoff's law of refrac- 

 tion for electrical currents ; so that it is possible- as shown by 

 Humboldt and Gay Lussac to carry an electrical fish between 

 two movable electrical plates that are in contact, without dis- 

 turbance from shocks. This fact was compared by the elder 

 Becquerel to the well-known experiment in which the secondary 

 twitch from muscle to nerve (Matteucci's contraction) may be 



