XI 



ELECTRICAL FISHES 427 



muscle, a discontinuous change of state in the organ. That is to 

 say, it causes repeated discharges at the rhythm of the excitation, 

 which summate into a true electrical tetanus, as may be proved 

 each time by the secondary tetanus of a rheoscopic frog's leg lying 

 on the organ, or otherwise brought into the discharging circuit. 

 From observations with galvanometer and telescope Sachs describes 

 the phenomenon of electrical tetanus (at great distance of coil) in 

 the Gymnotus organ as follows : " The thread moves slowly up- 

 wards in an absolute, positive direction (i.e. according to that of the 

 direction of the discharge), pauses there with twitching up-and- 

 down movements, and then falls again after a short time, although 

 not to the zero-point. Sometimes the thread will suddenly rise 

 again from the initial height at which it rests. When tetanus 

 ceases, the thread drops quickly as though released (4 e, p. 193). 

 Eapid succession of the single induction currents is essential on 

 tetanising the organ from the nerve, since even the most rapid hand 

 make and break of the current from 4 Groves proves ineffective. 



In Malapterurus also, according to Babuchin, the tetanisation 

 of the electrical nerves is followed by discontinuous discharges, 

 which last for a longer or shorter time according to the vitality 

 of the organ -preparation. "The shocks can be felt with the 

 fingers, and make the same impression as when the fingers actually 

 touched the inductorium." 



The trunk-fibres of the electrical nerves of Malapterurus were 

 found by Babuchin to be little sensitive to tetanising currents. 

 This seems partly due to the thick perineurium, since currents 

 that failed to excite the thick fibres of the trunk excited the 

 thinner branches effectively. Schonlein (30), too, on tetanising 

 the nerves to the organ of Torpedo with the rheotome (in order 

 to determine the time-distribution of the discharge), found the 

 threshold of stimulation to be very high in comparison with the 

 stimulus required by frog-preparations, and he is inclined to refer 

 this solely to the large size of the electrical nerves. The diameter 

 in large specimens is over 4 mm., and the cross-section is fifty 

 times as great as in an average frog's sciatic. And, in fact, on 

 splitting up the fibres of an electrical nerve " until the bundles 

 were as fine as in the frog's sciatic," Schonlein found that " the 

 distance of coil for minimal stimulation lay within the same 

 range as for the frog," a fact that is of great importance in the 

 question of immunity, which we shall presently discuss. 



