cox AND OTHERS: ELECTRIC TISSUE 491 



three times this length, but, in any group of longer specimens, the varia- 

 tions in voltage appear to be random. 



By measuring the peak voltage between electrodes 5 or 10 cm. apart 

 at different places along the organs, it is possible to compare the volt- 

 age per cm. in different parts. At the anterior end, where the number 

 of electroplax layers is greatest, the voltage per cm. is also greatest. 

 It decreases caudally, as the electroplax layers thicken. The voltage 

 per electroplax layer is roughly uniform along the organs. In four 



T 



t » 



Figure 3. Oscillographic traces of the discharge of Electrophorus: 



(a) An impulse from Sachs' organs followed by five impulses from the main organs; sweep 

 period, 50 msec. 



(b) Impulses from the main organs, superimposed by successive sweeps; sweep period, 4 

 msec. (From Zoologica.) 



specimens, values from 0.11 to 0.16 volt were found at the anterior ends 

 of the organs. Somewhat lower values are found in the posterior parts, 

 but, over most of the length, the voltage per electroplax layer is 0.1 

 volt or more.^' ^ Values around 0.1 volt per electroplax layer are found 

 also in Narcine brasiliensis. In Narcine, however, and also in Torpedo, 

 the voltage of the organs varies widely with the condition of the fish. 

 When a conductor is connected between the electrodes, so that the 

 electric tissue produces an external current, the peak voltage is lower 

 than with the external circuit open. If care is taken not to tire the fish, 

 the voltages obtained with a given resistance are reproducible. The 

 resistance R of the external conductor being known, the external cur- 

 rent / is found from the measured voltage V, by the relation, / = V/R. 

 When conductors of successively lower resistance are employed, the 

 voltage continues to decrease, as the current increases. The results of 



