LIVING TORPEDOS IN BERLIN. 423 



circuit, according to the parallelepiped of forces 1 . For a complete 

 theory it would be necessary to take into account induction and 

 the manifold polarisations which exist, the main fact, however, 

 would remain unaltered by these considerations. 



4. Method of leading-off the Torpedo-shock into an 

 experimental Circuit. 



Difficulties are met with in the endeavour to carry out the same 

 principles in leading-off the Torpedo-shock in the most satisfactory 

 manner. The dorsal and ventral surface of each organ must have 

 a metallic cover applied to it, and these covers must be led off from 

 their median edges which, for reasons hereafter to be mentioned, are 

 the most positive points on the back and the most negative points 

 on the belly (see p. 430). 



If the fish is in air nothing stands in the way of such a leading 

 off; and Boll who simply fixed his Torpedo, used guttapercha 

 plates lined with tinfoil after the pattern of my leading-off cover 

 for Malapterurus, one of these plates being in as close contact as 

 possible with the dorsal and the other with the ventral surface of 

 the electrical organ 2 . But if the fish remains in the water it is no 

 easy problem to apply the plates to the ventral surface of the 

 organ ; and it is still more difficult to insulate the rest of the fish at 

 the same time, which is, however, especially desirable on account of 

 the conductivity of sea water 3 . All this may be effected with such 

 a fish provided that it is laid down in the experimental tub upon 

 a guttapercha plate of greater extent than its body, the plate being 

 provided with two metal shields corresponding to the organs, the 

 median edges of these shields being in connection with one end of 

 the experimental circuit. A guttapercha plate must at the same 

 time be placed upon the back and moulded to its convex form. 

 This plate must also bear two suitable shields applied and led 

 off in the same manner. The root of the tail must be left free, 

 but the two plates surrounding the body must be everywhere in 

 connection with each other. 



Unfortunately this plan theoretically so faultless is by no means 

 convenient in practice. The fish refuses to lie on the lower plate 



1 See Helmholtz, loc. cit. p. 219. In the Gesammelte Abhandlungen, I gave an 

 explanation of the different action of the long and short lining which I had less 

 thoroughly thought out ; in this the insufficiently determinate conception of a ' mean 

 tension of the lining ' was introduced. In place of this explanation the one given in 

 the text must be taken. 



2 Reichert und du Bois-Reymond's Archiv fur Anatomic und Physiologic, 1873, p. 78. 



3 Compare Arthur Christian! in the Untersuchungen, pp. 41 1 et seq. 



