572 THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



ventral and dorsal skin is extremely small, and only appears as the 

 after-effect of any prolonged organ activity. In the excised organ there 

 is always a difference, but this is dependent upon the extent of the 

 mutilation involved in its excision. The amount is always greatest 

 immediately after the necessary incisions have been made, and then 

 dwindles until in half-an-hour it is comparatively small. It may, 

 however, be renewed by a fresh mutilation, especially that produced by 

 dipping the organ preparation for a brief period in - 6 NaCl at 80° C. ; 

 such immersion causes death of the surface tissue, whilst the internal 

 columns remain uninjured. 1 



A piece of organ treated in this way shows a large difference, the 

 dorsal end being galvanometrically positive to the ventral. The sign of 

 the electromotive change is independent of the seat of the injury ; it is 

 indifferent whether the sides, dorsal end, or ventral end is the part 

 affected ; the resultant effect is always that the dorsal end becomes 

 galvanometrically positive to the ventral. The extent of the change, on 

 the other hand, is definitely related to the amount and position of the 

 injury; it is greatest when the injury involves all the sides of the 

 columns, i.e. all the entering nerves ; it is small when the ends alone 

 are injured, since under these conditions the mutilation spreads but a 

 short distance along the sides of the subjacent columns. An effective 

 mutilation is thus one which involves local injury and hence excitation 

 of the nerves which enter at the sides of the columns, whilst the 

 resultant electromotive change is always similar, both as regards sign 

 and character, to that of functional activity. It thus seems not impro- 

 bable that the resting organ current of du Bois-Eeymond should be 

 regarded as an instance of that prolonged residual effect which will be 

 described as succeeding every intense organ response, and if so, then 

 no organ current apart from that due to activity has been observed. 



This view is confirmed by experiments upon the organ of the skate, 

 where the excitatory response is one in which the caudal end of the 

 organ columns becomes galvanometrically positive to the cephalic end. 

 Here, too, the organ current may be produced by injury, and, when thus 

 caused, is always similar both in direction and character to the residual 

 effect of the response. 



In the organ of Malapterurus, very little residual effect is observed 

 to follow functional activity, and the response appears to be never 

 succeeded by that prolonged residuum which is so characteristic a 

 feature in Torpedo ; it is most suggestive that in this fish the resting 

 organ current is either absent or very small, even when excised strips 

 through the entire organ are examined. 2 



Conditions affecting the magnitude of the excitatory response 

 of the organ.— The functional response of a nerve organ preparation 

 can be evoked by such a stimulus as the passage of a sufficiently intense 

 electrical current, whether this traverse the nerve or the isolated organ. 

 For the present the terminology employed in muscle may be used to 

 denote this distinction, the first being termed a response to indirect, the 

 second that to direct electrical stimulation. Whichever method is 

 employed, the magnitude of the response, as determined by that of 

 either the galvanometric deflection or the excursion of the capillary 

 electrometer, varies under a variety of conditions as follows : — 



1 Gotch, Phil. Trans., London, 1887, vol. clxxviii. B. 



2 Gotcli and Burcli, ibid., 1896, vol. clxxxvii. B. 



