384 OBSERVATIONS AND EXPERIMENTS 



3., Frog-alarum and frog-interrupter. 



One of the greatest improvements which I made in the method 

 of these experiments, consisted in perfecting a contrivance which 

 Galvani had already used in 1797 in his experiments on the 

 Torpedo 1 , namely, in employing a nerve muscle preparation of the 

 frog, in order to make the twitches produced by the shock serve a 

 double purpose. 



First, the preparation indicates that the fish has discharged, as 

 to which no certainty can otherwise be had, as the shock pro- 

 duces no visible effect in the fish itself, and the absence of any 

 action in the experimental circuit may be dependent on defect in 

 the circuit. Galvani and Matteucci were content with laying 

 the frog preparations on the Torpedo itself and observing the 

 twitches. I diverted a part of the discharge passing through the 

 mass of water in the experimental tub, led it through the nerves 

 which were in contact with the ring electrodes of the ' moist exci- 

 tation tube,' and let the muscle indicate its contraction by ringing 

 a bell. This was the origin of the ' frog-alarum 2 ,' which is 

 described in detail, and of which a diagram is given in a former 

 paper, and I will therefore not repeat it here. Within the limits 

 of accuracy there stated, the frog-alarum affords a means of watch- 

 ing the electrical activity of a fish in the experimental tub for 

 many hours together (comp. above, p. 377). If the electrodes of 

 the excitation tube were connected by wires with the iron hoop of 

 the landing-net and with a small iron disk at the bottom of the 

 net, the frog-alarum indicated the discharges made by the fish 

 during its removal from the trough to the experimental tub, but 

 for the most part, these did not begin to act until the fish emerged 

 from the large mass of water in the trough 3 . 



1 Memorie sulla Elettricita animale . . . al celebre Abate Lazzaro Spallanzani, 

 Bologna, 1797, 4. p. 74 ; Opere edite ed inedite ec. Bologna, 1841, 4. pp. 411, 412. 

 Matteucci made use of the same contrivance without naming Galvani (Essai sur 

 les phenomenes electro-physiologiques des Animaux, Paris, p. 144 ; Lezioni di 

 Elettro-Fisiologia ec. Torino, 1856, p. 2; Corso di Elettro-Fisiologia ec. Torino, 1861, 

 p. 115). 



2 See * Description of some apparatus and modes of experiment,' etc., Gesammelte 

 Abhl. vol. i. p, 213. (Fig. n with its description are interpolated from a previously 

 published paper, not included in this volume. Ed.] 



3 Comp. above, p. 380. Gay-Lussac had already observed the intensifying of the 

 discharges in Torpedos, when they were lifted out of the water (Humboldt, Obser- 

 vations, etc., p. 79). The fact recalls the disappearance of the current of a gastro- 

 cnemius immersed in a dilute salt solution. 



