ELECTRO-PHYSIOLOGY. 335 



sufficient to press the fisli lightly with the upper plate in order to have the dis- 

 charge, and thence to obtain the electric effects in the circuit of the copper wire. 



If it is proposed to produce the heating of the platina wire, I take a piece as 

 fine as possible, and form of it a small spiral ; with this I connect the two ex- 

 tremities of the copper wire united to the plates. Ou provoking the torpedo to 

 give several discharges in succession, the platina wire will be found to have bo- 

 come perceptibly heated. Magnetization is obtained by closing the circuit with 

 the usual small spiral of copper wire, in which is placed a needle of steel ; after 

 the discharge the needle is found to be magnetized, and the position of the poles 

 indicates the direction of the discharge. To obtain the indications of electro- 

 chemical action, we unite to the extremity of each of the copper wires two 

 pieces of platina wire, and these are placed with their extremities on paper pre- 

 pared with a mixture of starch and ioduret of potasBa. Each time that the 

 torpedo gives the discharge there is a blue spot formed under the extremity of 

 the platina wire which is united to the plate resting in contact with the back of 

 the animal. 



It is rather more difficult to obtain the spark of the discharge, and the reason 

 is clear, because it is necessary that at the moment the animal yields the dis- 

 charge there should be between the extremities of the circuit not a perfect com- 

 munication, but a slight interval of air, in which the spark is transmitted. 

 Among different means Avhich I have devised for the purpose, that which suc- 

 ceeds best is to connect one of the usual copper wires with a large iron file, and 

 while the fish is lightly pressed with the upper plate with a view to induce tho 

 discharge, to pass the other copper wire over the file. By operating thus in tho 

 dark, the spark is not long in making its appearance on the file. It was in this 

 way that I obtained the phenomenon in experimenting at Naples, on a living 

 gymnotus, during the scientific congress of 1845. 



In order to ascertain the effect of the discharge on the galvanometer, we 

 should have two laminte of platina united to the wires of the instrument, and 

 touch with these laminaj the two faces of the organ of the torpedo on which are 

 spread galvanoscopic frogs. Whenever the fish yields the discharge, the frogs 

 contract and the galvanometer shows a prompt deviation. Any galvanometer 

 of 500 or 600 coils, with a system judiciously astatic, suffices for the experi- 

 ment. The constant result is, that in the circuit of the galvanometer a current 

 passes directed from the back to the belly of the fish. It is worth noticing that 

 on introducing into the circuit of the galvanometer a liquid stratum somewhat 

 long and divided by diaphragms of platina, if the fish be quite vivacious, the 

 current indicated by the galvanometer undergoes no variation from the re- 

 sistance introduced into the circuit. 



If the operation be conducted after the surface of the fish is wiped dry, and 

 when some little enfeeblement has taken place, it will be soon apparent that the 

 discharge is stronger at those points of the organ which are thickest, that is, in 

 proximity with the median line of the animal. Hence it is that on touching 

 with the extremities of the galvanometer two points of the same face of one of 

 the organs, provided they correspond to different thicknesses, we have the dis- 

 charge ; if the back be touched, the discharge proceeds from the thicker points 

 of the organ to those less thick ; if the ventral face of the organ be touched, the 

 discharge passes from the thinner points of the organ to those which are thicker. 

 For the same reason and by the same law the discharge is procured ou 

 touching upon the same face two non-symmetrical points of the two organs. 

 From this we may infer why it is that the galvanoscopic frog well isolated con- 

 tracts if a long piece of its nervous filament is extended ou the organ. 



I will mention, finally, that on cutting perpendicularly one of the organs of 

 the living torpedo, the discharge is obtained in the galvanometer by touching 

 with the ends of platina two points of the incision, and that this discharge is 

 proportionably stronger as the points touched are further fron^ one anoiher, ti:io 



