THE ELECTROMOTIVE FORCE OF THE RESPONSE. 583 



was fresh, although only two or three times when it had been kept for 

 over twenty-four hours. 



The residual effect of the response. — In Torpedo the electromotive 

 changes, due to the excitatory explosion, are followed by others of the 

 same sign ; these may be termed residual effects, and are not improb- 

 ably strictly analogous to the negative after-effect observed in both 

 muscle and nerve. In the organ of Malapterurus they are of small 

 amount, and it is of interest to note that, in this fish, the so-called 

 resting current of du Bois-Eeymond is also inconsiderable. In the organ 

 of Torpedo and in that of the skate, such residual effects are far more 

 marked. 1 The simplest experiment suffices to show the change. A 

 strip of organ with its attached nerve is connected with a galvano- 

 metric circuit, and any existing difference of potential is carefully 

 compensated. The galvanometer circuit is now disconnected, and the 

 organ excited several times by stimulating its nerve. On again con- 

 necting the galvanometer, although the excitatory explosions have had 

 ample time to develop and subside, the dorsal end of the Torpedo 

 columns is found to be galvanometrically positive to the ventral. This 

 wake or residuum of the excitatory disturbance slowly subsides ; it 

 resembles the initial response in sign, but is unlike it in other respects, 

 since the change is of comparatively low electromotive force, and sub- 

 sides slowly. It is of interest, not merely because it accounts for the 

 so-called resting difference, but also because its presence shows that the 

 molecular disturbance, which is the basis of the pronounced shock, is 

 such that the tissue does not completely regain its poise for some con- 

 siderable time. It must be remembered that, since the residual effect 

 is present in every disc, the change observed in a preparation is the sum 

 of such effects in all the discs constituting the columns. In any one disc 

 it is thus of very small amount, but is magnified into a distinct effect 

 by the pile arrangement of the tissue. 



The electromotive force of the response. — Various methods have 

 been employed for this interesting determination. These have been 

 chiefly concerned with the electromotive force of the discharge which 

 is obtained from an uninjured electrical fish, but it is probable that 

 the intermittent character of the effect in such cases only allows of 

 an approximate determination. In Torpedo the telephone results 

 of Schonlein gave an electromotive force of 30 volts, or over; 2 in 

 Malapterurus the total electromotive force must certainly be at least 

 six times as great as this. With the excised organ the electromotive 

 force of a single response may be ascertained within certain limits, 

 either by balancing the effect, when a known rheotomic fraction of the 

 response is permitted to traverse a galvanometric circuit, or by analysing 

 the photographed curves of the excursion of the capillary electrometer pro- 

 duced by such a response. If the strip of organ stimulated is subsequently 

 prepared for microscopic purposes, the number of discs placed in series in 

 the strip can easily be counted, and thus the electromotive force of the 

 change in any one disc can be calculated, on the supposition that all 

 such discs are the seat of similar changes. In this way it has been 

 found that in the comparatively feeble organ of the skate the change in 

 each disc amounts to about 0'03 volt, in Torpedo to about - 04 volt, 

 in the powerful organ of the Malapterurus it may reach as much as 



1 du Bois-Reymond, loc. cit. ; Gotcli, loc. tit. 



-Schonlein, Ztschr. f. Biol., Munchen, BJ. xxxiii. S. 408. 



