ELECTRICAL CHARACTERISTICS OF 

 ELECTRIC TISSUE 



By R. T. Cox, C. AV. Coaxes, and M. Vertner Brown 



The Department oj Physics, The Johns Hopkins University, Baltimore, Maryland; 



The New York Aquarium, New York Zoological Society; and the 



Department of Physics, College of the City of New York. 



The group of electric fishes comprises a number of very different 

 varieties, both fresh water and marine. All of them possess special 

 organs capable of producing transient electric discharges, which, in 

 some species, are quite weak, but in others, are powerful enough to give 

 a severe shock. These organs vary widely among the different species 

 in their shape and size and in their position and orientation in the body 

 of the fish. They are alike in having a common unit of structure, the 

 electroplax. 



The arrangement of the electroplaxes has its highest geometrical regu- 

 larity in the electric rays, Torpedo and Narcine}' ^ In the electric or- 

 gans of these genera, they are piled in columns, an average one of 

 which contains about 400 electroplaxes in Torpedo marmorata and per- 

 haps 300 in Narcine brasiliensis. Each column extends from the ven- 

 tral to the dorsal surface of the body. A number of them, side by side, 

 form each of the two electric organs, which lie in the disk-like body of 

 the fish to the right and left of the body cavity, just outside the line of 

 gill slits. In each organ, there are four or five hundred columns in 

 Torpedo marmorata and Narcine brasiliensis, and about a thousand in 

 T. occidentalis. During the discharge, the current traverses each organ 

 in the direction from its ventral to its dorsal face. Thus, the columns 

 of electroplaxes discharge in parallel, while, within each column, the 

 electroplaxes act in series (figure 1). 



In Torpedo and Narcine alike, the electric tissue comprises about one 

 sixth of the whole volume of the fish. In the electric eel, Electrophorus 

 electricus, it makes, by contrast, about one half. Organs of such a size 

 must conform, in part, to the shape of the fish, and hence there cannot 

 be so regular an arrangement of the electroplaxes as in the rays. It is 

 customary to distinguish in Electrophorus three pairs of organs: the 

 main organs, which extend along the posterior four-fifths of the length 

 of the fish ; the much smaller organs of Hunter, which lie under the main 

 organs along their entire length; and the organs of Sachs, which lie 



(487) 



