Fishes of the Wester?! North Atlantic 8 3 



all the properties of electricity, being capable of producing a spark, of deflecting or 

 magnetizing a needle, of electrolyzing chemical compounds (e. g., of dissociating iodide 

 of potassium), and so forth; also, it is audible on a telephone suitably connected. 



It is commonly said that the production of the shock is under the voluntary 

 control of the Torpedo, both as to time of discharge and as to its strength. Electric 

 Rays, lying undisturbed on the bottom of an aquarium, have been observed (by tele- 

 phone) to give oft' a succession of discharges spontaneously; i. e., without any apparent 

 stimulation." However, the regularity with which a discharge follows when the skin is 

 touched or otherwise stimulated suggests that it is chiefly a simple reflex action induced 

 by tactile stimulation. It has long been known that the fish lies quiet for some little 

 time without further discharge after delivering a shock, and the delivery of several 

 discharges at rather brief intervals leaves it in an exhausted condition, after which it 

 requires a considerable rest period before it can discharge again. We may cite the case 

 of an Australian specimen of Hypnarce that delivered 50 successive shocks within about 

 ten minutes, intense at first but weakening until hardly discernible. ^^ And it has been 

 observed in laboratory experiments that the voltage and power decline rapidly as the 

 fish becomes increasingly fatigued. 



The individual discharges or pulses, each lasting perhaps 0.03 second, follow 

 one another in rapid succession" in trains. In Torpedo nobiUana of the western Atlantic, 

 the number of pulses per train appears to average about 1 2 but may go as high as 

 100, exceptionally more than that. Either one train, or a few trains following one 

 another in rapid succession, constitute what is commonly termed a "shock." The 

 electromotive force of the discharge varies not only from species to species and from 

 specimen to specimen of a given species but with the condition of the fish, while dif- 

 ferences in recorded results are partly to be explained as due to differences in the sen- 

 sitivity of the apparatus employed. Measured voltages range from as low as 8—17^* 

 to as high as 70— 80^* for the European Torpedo marmorata, with estimates going as 

 high as 200.1^ Seven to 37 volts, with various resistances, have been recorded for 

 Narcine brasiliensis\ 25 volts was recorded for one specimen of Torpedo nohiliana and 

 220 volts for another of about the same size, a divergence which illustrates the dif- 

 ferences in the electric capabilities of different specimens of the same species." This 

 last voltage (220), which probably approximates the maximum to be expected from any 

 Electric Ray, is about equal to that of the Electric Catfish {Malopterurus) of North 

 African rivers but falls considerably below that of the so-called Electric Eel (Electro- 

 phorus) of South America. 



The literature on the Electric Rays includes almost endless references, from 

 classic times down to the present, pertaining to the effects of the shocks received by 



II. Schonlein, Z.Biol., 31 (N. S. 13), 1S95: 451. 12. McCuUoch, Aust. Mus. Mag., i (3), 1921: 89. 



13. Rates reported as being up to 150 per second. 14. d'Arsonval, C. R. Acad. Sci. Paris, I2i, 1S95: 145. 



15. Cremer, Verh.Gesell. dtsch. Naturf., Art. 80, samml. Cologne, 1909 (2), 2 half. 2 grup.: 523. 



16. Gotch and Burch, Proc. roy. Soc. Lend., 65, 1900: 442. 



17. See Coates and Cox (Zoologica N. Y., 27, 1942: 28) and Cox and Breder (Zoologica N. Y., 28, 1943 : 49) for tabul- 

 ations of voltage, current, and power for Torpedo nobiliana and Narcine brasiliensis. 



