ELECTRICAL FISHES 425 



of which corresponds to an elementary motor impulse, producing 

 tetanic contraction of the muscle. Du Bois-Keymond proposes to 

 call each such elementary shock a " partial discharge " (" Theil- 

 entladung "), not to be confounded with the earlier local 

 (" Strecken-") discharges of the organ. The rate of the incomplete 

 discharges, which as Marey showed with the Marcel-Desprez 

 signal, as also with the capillary electrometer and telephone make 

 up a shock, depends much upon the greater or less energy with 

 which the animal reacts, and it falls with increasing fatigue or 

 cooling. There are usually some 25 shocks at a rate of 100 

 200, on an average 150 per sec. This gives a duration of the 



24 

 total discharge of + 0'07" = 0'23 sec., assuming for the 



.LOU 



duration of an incomplete discharge the figure cited by Marey for 

 the shock from the organ produced by a single impulse from the 

 nerve, i.e. ^" = 0-0 7". 



The buzzing sensation often noted in the shock of electrical 

 fishes is riot, in the opinion of du Bois-Keymond, to be referred to 

 the tetanic character of the discharge, since the partial dis- 

 charges follow too quickly, and a total discharge is too soon over. 

 He rather holds " this sensation to be due to a succession of total 

 discharges, which may become half fused, so as to form maxima 

 and minima of the curve uniting the maxima of the incomplete 

 discharges : hence there arises a double tetanising ctenoid " (4 e, 

 p. 239). 



Among artificial stimuli the electrical current is really the 

 only suitable means of studying the indirect excitation of the 

 organ exactly for the same reasons as in the nerve-muscle 

 preparation. In mechanical excitation (pinching, cutting) of the 

 electrical nerve of Torpedo, Schonlein (30) heard a "very slight 

 scratching noise " in the telephone, which could only be detected 

 when the room was quiet. Crushing the nerve between two glass 

 plates gave the same result. On the other hand, Babuchin found 

 the electrical nerve of Malapterurus to be sensible at all points to 

 mechanical stimulation. " The bisection of the trunk, and also of 

 its branches, with sharp scissors, pressure, stabbing with a thorn 

 or pointed glass needle, never failed in effect." Chemical stimu- 

 lation (bathing in saturated solutions of sodium or potassium salts) 

 was practically inactive. In electrical excitation, single induction 

 shocks acted, if at all, only at high intensities. Sachs was unable 



