ANIMAL ELECTRICITY. 



87 



every possible precaution, he could neither, in 

 the light, detect the slightest indications of the 

 passage of electricity through even very small 

 intervals of air, nor observe a spark in the dark. 

 He was equally unsuccessful in using an elec- 

 troscope formed on the principle of Coulomb's, 

 which displayed sparks when touched either 

 with a small rod of glass slightly excited, or of 

 sealing-wax. He varied the trials, using highly 

 rarefied air at ordinary temperatures, and also 

 condensed air deprived of moisture, with the 

 same negative result. He insulated the fish on 

 a plate of glass, wiped its margin dry, and 

 besmeared it with oil, but no spark could be 

 procured. 



Dr. Davy was more successful in obtaining 

 indications of the evolution of heat during the 

 torpedo's discharge. He used Harris's electro- 

 meter, and saw proof of an elevation of tem- 

 perature in the motions of the fluid in the air- 

 thermometer; thus corroborating the prediction 

 of Dr. Faraday, who was previously convinced 

 that, by means of this instrument, the evolution 

 of heat by animal electricity would be made 

 evident. Dr. Davy made several experiments 

 with the view of ascertaining whether very fine 

 platina wire might not be ignited in the passage 

 of the electricity of the torpedo, but never 

 witnessed the expected effect. Upon this he 

 remarks, " This want of ignition may, at first 

 view, seem contrary to the effect on the ther- 

 mometer ; but perhaps it ought not to be con- 

 sidered so, taking into account the rapid mau- 

 ner in which the heat evolved in the fine pla- 

 tina wire must be carried off by the adjoining 

 compound wire of platina and silver."* 



From the discharge of the Gymnotus, Walsh, 

 Fahlberg, Guisan, and other observers of the 

 last century, obtained sparks. Walsh attached 

 a thin sheet of pewter to a plate of glass, cut a 

 very fine slit in it, and then passed the discharge 

 along the metallic sheet, the fish being at the 

 time out of the water. A spark was very dis- 

 tinctly seen at the margins of the slit. Fahlberg 

 of Stockholm used the same kind of apparatus, 

 but with gold leaves instead of pewter, and 

 placed the margins of these about a line apart. 

 Dr. Williamson fixed two brass rods in a frame, 

 and brought their points to within one-hundredth 

 of an inch of each other, but, although the dis- 

 charge of the gymnotus passed from one rod to 

 the other through the intervening air, there was 

 no spark. Humboldt watched an active Gym- 

 notus for a long time during the night, and 

 irritated it so as to obtain from it many sharp 

 discharges, but he saw no spark. 



VIII. Results of experiments in which the 

 nerves, electrical organs, and other parts were 

 mutilated. The general result of these experi- 

 ments is, that destruction of the communications 

 between the electrical organs and the nervous 

 centres is followed by annihilation of the power 

 of discharging. 



According to Mr. Todd, (whose experiments 

 were made on the torpedo at the Cape of Good 

 Hope,) it is necessary to cut through all the 

 nerves going to the electrical organs to destroy 



* Phil. Trans. 1834. 



their peculiar powers. He cut through all on 

 one side, and some on the other, but still 

 shocks were given. He also lacerated the 

 organs themselves extensively, without destroy- 

 ing the discharging power. Mr. Todd found 

 that fishes in which all the electrical nerves had 

 been cut appeared more vivacious after the 

 operation than before it, and actually lived 

 longer than others not so injured, but which 

 were excited to discharge frequently.* 



In repeating Mr. Todd's experiments, Dr. 

 Davy obtained very similar results; but he 

 mentions that " when a small portion of brain 

 was accidentally left, contiguous to the elec- 

 trical nerves of one side, and with which they 

 were connected, the fish, on being irritated, 

 gave a shock to an assistant, who grasped the 

 corresponding electrical organ ."f 



Spallanzani found that the torpedo loses its 

 power of giving shocks after the aponeurotic 

 covering of the electrical organs is removed ; 

 but that the cutting out of the heart does not 

 lessen this power until the animal life begins to 

 suffer from the loss of blood. 



Humboldt cut a Gymnotus through the mid- 

 dle of the body transversely, and found that the 

 anterior portion alone continued to give shocks. 



Experiments of this kind have not yet been 

 performed on the Silurus ; but, judging from 

 the structure of the organs in this fish, we have 

 every reason to expect that the results of such 

 experiments on it would be the same, ^hile 

 we would not be understood to sanction the 

 wanton repetition of experiments such as these, 

 which cannot but be productive of much suffer- 

 ing to the subjects of them, we must yet repeat 

 here the suggestion recently made by Professor 

 Miiller of Berlin with regard to future experi- 

 ments on the Gymnotus and Silurus. He points 

 out how very desirable it is to ascertain whether 

 the double organs of these fishes act as opposite 

 electromotors, which might be determined by 

 cutting out one organ from either side, and then 

 exciting the fish to discharge. The same dis- 

 tinguished physiologist remarks that if he had 

 an opportunity of experimenting on the torpedo, 

 his first experiment should be, after having cut 

 through the nerves going to the electrical organs, 

 to irritate their cut extremities, still in connexion 

 with the organs, with mechanical and galvanic 

 stimulants, with the view of discovering whether 

 these would excite the organs to discharge their 

 electricity.! 



IX. Anatomy of the electrical organs. The 

 experiments referred to in the former section 

 sufficiently demonstrate that the manifestation 

 of the peculiar power possessed by electrical 

 fishes depends on the integrity of the connexion 

 between their nervous centres and certain 

 organs of a peculiar structure, which have 

 been named the electrical organs. These have 

 been particularly examined in the Torpedo, 

 Gymnotus, and Silurus, by several anatomists, 

 and no doubt is entertained that they, together 



* Phil. Trans. 1816. 

 t Phil. Trans. 1834. 120. 



t Handbuch der Physiol. des Menschen. Co- 

 blenz. 1833. 



