On the Electric Organ in Malapterurus electricus. 437 



Since the constants of this particular electrometer had been accu- 

 rately determined, it might have appeared feasible, after measuring the 

 resistance of the preparation and the resistance of the shunt, to calcu- 

 late the E.M.F. of the Malapterurus shock directly from the photo- 

 graphic record. Such a method would not, however, have been satis- 

 factory, owing to the character of the experimental conditions obtaining 

 in the present research, and it was deemed preferable to obtain the 

 comparison curves given by an E.M.F. nearly comparable with that of 

 the organ response, for the following reasons. The meniscus of the 

 electrometer indicates the E.M.F. acting upon it at any moment, 

 partly by its position above or below zero, and partly by the velocity 

 with which it is moving at that instant, the position being measured in 

 divisions of an arbitrary scale, and the velocity by the subnormal to 

 the curve, expressed in polar co-ordinates. But the ratio between the 

 value of a division on the subnormal and a division on the scale varies 

 with the resistance in circuit, and is consequently affected by the use 

 of a shunt. Obviously, therefore, the simpler method, and the one- 

 least open to objection, was to photograph the normal excursion given 

 by an E.M.F. not many times smaller than that of the organ response 

 through a circuit as nearly as possible similar to the actual one, i.e., 

 through an equivalent resistance and through the identical shunt. 

 The organ itself could not be employed for this purpose, because even 

 if it gave no response to such a stimulus, the possible effects of electro- 

 lytic polarisation might impart to the record time-relations different 

 from those of a normal excursion. 



We therefore carefully measured the resistance of the preparation 

 with the leads in the position employed in obtaining the curves referred 

 to previously (No. 3012 and 3013); we then substituted for it an 

 equivalent non-polarisable, non-inductive resistance, and photographed 

 the excursions given on throwing in a constant E.M.F. of 9 volts 

 through this circuit with a shunt of three-lamps for comparison with the 



Fig. 2. 



Analysis of No. 3012, showing the E.M.F. of the single shock of 15 mm. of 

 electrical organ, and representing about one-eighth part of the E.M.F. of the 

 shock from the entire fish. 



