XI 



ELECTRICAL FISHES 



411 



(4 g, h) finally decided on the arrangement shown in Fig. 268, as 

 the most convenient for leading off from the torpedo in water. 

 A circular zinc-plate, covered with flannel, about the same size 

 as the body (v vj, was placed at the bottom of a glass vessel 

 30 cm. wide and 10 cm. deep. A portion of the zinc was bent 

 outwards for leading off. The fish lay upon the flannel. The 

 dorsal shield, for leading off from the back, is again a zinc-plate 

 shaped to the fish with the edge turned up ; the upper surface is 

 lacquered, and a wooden knob in the middle carries the second 

 wire for leading off. 



By this method it is easy to lead off the shock, and to 

 experiment without injuring the animal. A valuable instru- 

 ment, with many applications, is the nerve-muscle preparation 



FIG. it>i ;. 



Fit;. -T'7. 



of a frog, employed as early as 1797 by Galvani, and later again 

 by Matteucci, in experiments on Torpedo. Du Bois-Eeymond 

 constructed the so-called "frog-alarum" (Fig. 268, FW), by lead- 

 ing off part of the discharge that was passing through the water 

 containing the fish, by means of a pair of submerged electrodes, 

 to the nerve of a rheoscopic leg, the muscle of which rang a bell 

 when it contracted, and thus indicated the successive dis- 

 charges of the organ. In this way the electrical activity of a 

 fish under water can be observed with little trouble and absolute 

 certainty for hours at a time. 



Schonlein (30) has recently employed the telephone for the 

 same purpose, with very good results. He connected one end of 

 it with a lead plate lying 011 the floor of the fish-trough, while 

 the wire from the other pole ended in a smaller lead plate, that 

 dipped into the water. Even in weak animals (Torpedo} 



