XI 



ELECTRICAL FISHES 431 



IV. TIME-DISTRIBUTION OF DISCHARGE FROM ELECTRICAL 



FISHES 



Seeing the close relation between most, if not all, electrical 

 organs, and striated muscle, it is interesting to compare the time- 

 distribution of the twitch, or accompanying current of action, 

 with that of the discharge. In the first place it must be asked 

 whether, with a single momentary stimulus, there is any latent 

 period of the elementary discharge which it elicits from the 

 organ. Marey at first decided in the affirmative for Torpedo. 

 By means of a pendulum-myograph the circuit (in which there was 

 a rheoscopic frog's leg, as well as the organ which was excited 

 from its nerve by single induction shocks) could be closed for a 

 moment at any given time after the excitation, so that a fraction 

 = ^Ly" was cut out of the discharge. This fraction, expressed 

 on the leg as a twitch, might therefore be shifted along the dis- 

 charge, so that on one hand the total duration ( T V')' on ^ ie 

 other the presence of a perceptible latency, could be determined, 

 since a certain interval between the fraction cut out and the 

 moment of stimulation was required in order to produce con- 

 traction. The time occupied by the conduction of excitation 

 from nerve to organ was thought by Marey to be negligible on 

 account of the shortness of the nerve. 



Another of Marey's methods was founded on the earlier 

 experiment of v. Helmholtz, by which the fraction of the negative 

 variation of the muscle current that discharges a secondary 

 twitch was determined. Two twitches of a frog's nerve-muscle 

 preparation were graphically recorded, one being discharged 

 directly by an induction shock, the other through the discharge 

 of the organ, generated by the induction current at the same 

 position of the indicator (Fig. 272). The displacement of the 

 curves corresponds with the latent period of the discharge, and 

 less with the time lost in nervous conductivity, which is again 

 neglected, although Marey had already remarked that excitation 

 travels more slowly in electrical than in frogs' nerves, as was 

 subsequently confirmed by Jolyet and Gotch. Gotch determined 

 the commencement of the galvanometer effect on a nerve-organ 

 preparation by stimulating the nerve at points farthest from and 

 nearer to the organ. If the distance amounted' to 13 mm. the 

 galvanometer effect began YO%O" earlier on stimulating the 



