ON LIVING MALAPTERURUS. 



385 



The second purpose for 

 experiments on electrical 

 fishes is the following. The 

 frog-alarum teaches that 

 the excited Malapteruras, 

 if it is at all vigorous, 

 seldom discharges once 

 only. Generally two or 

 three strokes of the bell 

 occur, sometimes follow- 

 ing each other closely, 

 sometimes separated by a 

 longer interval. Without 

 having recourse to other 

 means, it is therefore im- 

 possible to ascertain the 

 effect which any given 

 condition exercises on the 

 strength of the branch 

 current led into the ex- 

 perimental circuit. For it 

 always remains doubtful, 

 whether the differences 

 observable result from 

 that condition, or from the 

 varying number and suc- 

 cession of the discharges. 

 For reasons easily under- 

 stood, nothing could be 

 effected here with the 

 usual mechanical means. 

 But it is obvious that the 

 frog-preparation might be 

 relied on for the timely 

 opening of the experi- 

 mental circuit after exci- 

 tation by the first shock. 

 With a given nerve- 

 length and a muscle of 

 given size and effi- 

 ciency, the muscle raises 



which the frog-preparation is adapted in 



Fig. II. E and E t) zinc electrodes in the trough 

 containing the fish. F, H, & the bell, hammer, 

 and muscle arranged to form an alarum, a, p, q, 

 lever of the frog-interrupter. G-,/, its muscle, p, the 

 platinum point which rests upon the supporting 

 plate, q, amalgamated copper wire which dips into 

 mercury. K, K,, keys. B, galvanometer. The 

 action of the interrupter is such, that only one 

 shock can pass through the galvanometer, for by 

 the contraction of the muscle G,, the galvanometer 

 circuit is broken at q and not again closed. The 

 alarum of course goes on ringing. 



C C 



