Muscle and Electric Organs 619 



lasts about 2 msec.'^'^- '^•^' '**' (Fig. 237). In Torpedo occidentalis spike dura- 

 tion is 3.5 msec. In the electric eel there may be, in addition to the larger 

 spikes, minor discharges either preceding a major discharge or appearing in- 

 dependently."- The minor discharge arises in the small organ of Sachs sepa- 

 rate from the main electric organ. These minor discharges occur when the 

 fish are cruising about for food, and there is good evidence that prey are lo- 

 cated by the reflection of electric waves. 



The synchrony of the electric discharge is remarkable and is essential for 

 maximum power output. The two organs of Torpedo discharge within 0.1 

 msec, of each other! In the electric eel each point in the electric organ is 

 positive with respect to all points behind it, and measurements of time dif- 

 ference between the two ends indicate a wave travelHng 450-2500 M./sec. 

 Propagation stops at a cut in the spinal cord.''^ There is evidence that when 

 Electrophorus is probed with an active lead while a ground lead is placed 

 on the tank, a point about one third of the distance back is electrically neu- 



.v«^A^A. 





■> "^ 



L 



Fig. 237. Electric organ discharge in Electrophorus. Upper, records showing small 

 followed by large pulses; lower, records at higher speed to show shape of discharges. 

 From Coates, Cox, and Granath.'" 



tral. This near synchrony of all parts of the electric organs indicates very 

 precise timing in the central nervous system; the motor impulses going to 

 distant electroplaxes must leave the brain earlier or travel faster than do 

 the impulses to near parts of the organ. 



The total peak voltage measured without external resistance is usually 

 20-30 volts in Torpedo marmorata, 230 volts (sometimes 500-600 v.) in Elec- 

 trophorus.^'-^- ^-^ Older measurements are somewhat lower. In Electrophorus 

 the thickness of the plates increases from the anterior end backward, and 

 the voltage per centimeter length diminishes (Fig. 238). The calculated 

 peak voltage per electroplax is remarkably constant at 0.05-0.15 v. per plate 

 for all species investigated. 



The voltage has been measured for various shunting external resistances 

 and the current output calculated. Zero current corresponds to the maximum 

 voltage and, as current increases, voltage decreases linearly; the maximum 

 current developed by the electric eel is less than one ampere, whereas from 

 the lower-voltage ray fish higher currents are obtained (2 amperes for Nar- 

 cine and 60 amperes for Torpedo occidentalism. Power as a function of ex- 



