490 ANNALS NEW YORK ACADEMY OF SCIENCES 



long, the thickness of this single electroplax layer is about .01 cm. In 

 fish of this length, the cross-section of the organs near the anterior end 

 has an average area of about 30 cm^. Hence, the volume of the single 

 electropax layer is 0.3 cm-''. The organs taper caudally, but, as the 

 cross section decreases, there is a compensating increase in the thickness 

 of the layer, and the volume is nearly uniform over most of the length 

 of the organs. The structure is much as if uniform layers were assem- 

 bled in a long column, and then the column were drawn out thin toward 

 one end, the layers being changed in shape, but not in volume. 



These long organs found in Electrophorus offer remarkable advan- 

 tages in the study of the action of electric tissue in the living fish. The 

 series array of electroplax layers is accessible for electrical connection 

 all along its length, rather than only at the ends as in the rays. The 

 variation in structure makes it possible to compare in the same speci- 

 men the electrical characteristics of electroplax layers of very different 

 dimensions. Also, Electrophorus, which comes to the surface to breathe, 

 can be kept for some time out of water without injury, and the elec- 

 trical characteristics of its tissue remain constant during an interval in 

 which it can produce a thousand or more electric impulses. 



In our observations, the fish is removed from the water and laid in 

 a dry wooden trough. Electrodes made of aluminum strip 1 cm. wide 

 may be placed in any of a number of slots in this trough. These make 

 contact with the skin adjacent to the electric organs and, when they 

 are connected to a cathode-ray oscillograph, it is possible to record 

 photographically the discharge of the part of the organs included be- 

 tween the electrodes (figure 3). The measurements made with the 

 oscillograph are found not to vary appreciably with the area of con- 

 tact between skin and electrode, provided this area is not less than a 

 few square centimeters. Of course, no appreciable dependence on the 

 choice of a metal for the electrodes is to be expected, since the voltages 

 measured are very much greater than any contact potential differences. 



When the electrodes are at the extremities of the main organs of a 

 mature specimen, and the external circuit is open, so that there is no 

 electric current outside the body of the fish, the average peak voltage 

 is about 370 volts. ^ The highest voltage we have measured is 550. 

 There is also a discharge of much lower voltage, which is evidently pro- 

 duced by the organs of Sachs, since it is observed only when some part 

 of these organs lies between the electrodes. In immature specimens, 

 the voltages are smaller. The voltage of the main organs increases 

 with their length, at an average rate of 8 volts per cm., until the organs 

 attain a length of about 50 cm. The organs may ultimately attain 



