620 



Comparative Animal Physiology 



ternal load passes through a maximum at about 3 watts for Electro-phorus. 

 One large specimen of Torpedo occidenialis^'^ developed a maximum power 

 of 6 kw! 



Records made from single electroplaxes or groups agree well in duration 

 and voltage with those calculated from measurements of the total dis- 

 charge.'"^ Single electroplax discharges are all-or-none, with a rising phase 

 of 0.5-0.7 msec. Each discharge is monophasic because it is not propagated, 

 shows no after-potential, and is all-or-none except after fatiguing, where- 

 upon the voltage diminishes. A single stimulus to the nerve gives one dis- 

 charge of the electroplax. When the nerve fibers to a portion of an electric 

 organ are allowed to degenerate the organ becomes totally inexcitable.^"^ 

 Injections of curare or of atropine reduce the electric discharge to zero.'^ 



QCh.E. V/cm. 



\ I 



500--I94P 



400--15^ 



3o6__n,4 



200 --7. 6 



loo- -3.6 



10 



20 



Head end 



30-* cm. 

 Caudal end 



Fig. 238. Relation between potential and cholinesterase in electric organ of Electrophorus. 

 • , Average QChE; ■, volts per cm. From Nachmansohn, Cox, Coates, and Machado."^ 



In addition to being electrically similar to muscle end-plate, the electric 

 organ is chemically similar. The electric organ is the richest tissue yet as- 

 sayed for acetylcholine, having 40-100 micrograms per gram fresh weight, 

 or nearly 0.1 per cent dry weight. Acetylcholine appears in the eserinized 

 perfusate from an electric organ stimulated through its nerve.^^ Intraarterial 

 injection of as little as 2.5 fig. of ACh elicits a brief electrical discharge. 

 Injection of eserine prolongs the spike duration, promotes facilitation of 

 subliminal impulses, and hastens fatigue of the electric tissue.'"- Cholin- 

 esterase is high in concentration in electric organ tissue, and in the electric 

 eel the cholinesterase in centimeter lengths of the organ decreases toward 

 the posterior end along a curve similar to the curve for diminution in voltage; 

 i.e., the cholinesterase per electroplax tends to be constant (Fig. 238)."^ 



