cox AND OTHERS: ELECTRIC TISSUE 493 



others to follow, it is implied that the two paired organs discharge simul- 

 taneously. In Narcine and Torpedo, where the organs are far apart, 

 a simple experiment shows this is true. The evidence in respect to 

 Electrophoru.s points to the same conclusion, but it is not certain.) 



If opening the external circuit prevented any current in the organs, 

 the voltage measured with the circuit open would be equal to the elec- 

 tromotive force of the part of the organs included between the elec- 

 trodes. Then, the maximum voltage per electroplax layer would be 

 equal to the electromotive force of the layer, and its quotient by the 

 maximum current per cm.^ would be the resistance of 1 cm.- of the 

 layer at the peak of the discharge. However, even with the external 

 circuit open, there must be closed circuits within the body of the fish, 

 during the discharge. Consequently, the voltage per electroplax layer 

 must be somewhat less than the electromotive force of the layer. Its 

 quotient by the maximum current per cm.- is still of some significance 

 as a lower limit for the resistance of 1 cm.^ of electroplax layer. It 

 seems likely, also, that this lower limit is not very much less than the 

 actual value. In Electrophonis, minimum values thus found for the 

 resistance of 1 cm.- of electroplax layer have varied in different speci- 

 mens between 2 and 5 ohms. In two specimens of Narcine brasiliensis, 

 the values were about 1 ohm. 



It is interesting that, in Electrophorus, the resistance of unit area of 

 electroplax layer does not increase caudally, although the thickness of 

 the layer increases about ten-fold from the anterior to the posterior end 

 of the main organs. This suggests that the resistance resides prin- 

 cipally at boundaries in the electric tissue. 



From the observations considered thus far, it is seen that the single 

 electroplax layer in Electrophorus has characteristic electric quantities 

 which are roughly uniform, in spite of wide variations in the arrange- 

 ment of the electroplaxes and in the size of the fish observed. Also, 

 in those cases in which comparison has been possible, it is found that 

 these quantities have the same order of magnitude in Narcine and 

 Torpedo as in Electrophorus. 



We have studied, in a number of different specimens of Electrophorus, 

 the variation during an impulse of the electrical characteristics of the 

 tissue.* The oscillograph was connected, as already described, to 

 electrodes placed 10 cm. apart against the main organs of each speci- 

 men studied. Impulses with the external circuit open and closed, 

 through resistances from 400 to 50 ohms, were recorded photographic- 

 ally. With each specimen and each value of the external resistance, 

 measurements were made on a number of oscillographic traces at each 



