ANIMAL ELECTRICITY. 



97 



electricity than those of a phlegmatic tempera- 

 ment. 3. An increased accumulation of elec- 

 tricity takes place in the evening. 4. Spirituous 

 drinks augment its intensity. 5. The elec- 

 tricity of women is more frequently ne<jative 

 than that of men. 6. In winter, while the body 

 is very cold, no electricity is manifested, but it 

 gradually reappears as the body is warmed. 

 7. The whole body naked, as well as every part 

 of it, shews the same phenomena. 8. During 

 the existence of rheumatism, the electricity is 

 greatly diminished in intensity, but as the dis- 

 ease declines it again increases. Gardini found 

 that the electricity of women during menstrua- 

 tion and pregnancy is negative. 



Some individuals exhibit electrical pheno- 

 mena much more readily than others. Some 

 persons, for instance, hardly ever pull off articles 

 of dress worn next the skin without sparks and 

 a crackling noise being produced. It is related 

 of a certain monk that sparks were always 

 emitted from his hair when it was stroked back- 

 wards; and of an Italian lady that her skin, 

 when rubbed with a linen cloth, gave out sparks, 

 attended with a crackling noise. The same 

 phenomenon, as exhibited by the cat, and by 

 other animals covered with a soft fur, is daily 

 observed. But it has been stated that the cat's 

 electricity may be accumulated in its own body 

 and given off suddenly, so as to produce a 

 shock. Homer says,* " If one take a cat in his 

 lap, in dry weather, and apply the left hand 

 to its breast, while with the right he strokes 

 its back, at first he obtains only a few sparks 

 from the hair; but, after continuing to stroke 

 for some time, he receives a sharp shock, which 

 is often felt above the wrists of both arms. At 

 the same moment, the animal runs off with 

 expressions of terror, and will seldom submit 

 itself to a second experiment." In repeating 

 this experiment, we have obtained the like 

 result. 



We are not aware of any other observer having 

 met with any thing resembling an accumulation 

 of electricity in quadrupeds, excepting Cotugno, 

 who asserted that, in dissecting a living mouse, 

 he felt an electric shock when its tail touched 

 his finger.-f 



XI. Uses of animal electricity. The pur- 

 pose which the electrical function is fitted 

 to serve in the animal economy is proba- 

 bly not single. It is very evident that the 

 discharge from the organs frequently strikes 

 terror into the enemies of their possessors, and 

 thus it may be regarded as a means of defence ; 

 while, in certain circumstances, it may be useful 

 in enabling the fish more easily to secure its 

 prey. But this, probably, is not all. It is 

 very likely, as Dr. Roget has suggested,} that 

 the electrical organs communicate to the fish 

 perceptions of electrical states and changes in 

 surrounding bodies, (very different from any 

 that we can feel,) in the same way as other 

 organs of sense convey perceptions with regard 



* Gilbert's Ann. der Phys. B. xvii. 

 t Humboldt. Ueber die gereizte Muskel-und- 

 Nervenfaser. Berlin, 1793. i. 30. 

 $ Bridgewater Treatise, i, 31. 

 VOL. II. 



to light and sound. Such perceptions we can 

 conceive to be very useful and pleasurable to 

 animals living in the dark abysses of the waters. 



Some of Dr. John Davy's observations make 

 it very doubtful whether the electrical function 

 is ever subservient to that of prehension of food. 

 He kept young torpedos for a period of five 

 months or more, in large jars of salt water, 

 during which time they ate nothing, although 

 very small fishes, both dead and alive, were put 

 into the water. Yet they grew, and their elec- 

 trical energies and general activity increased.* 

 The small fishes seemed to have no dread of the 

 torpedos. On one occasion, however, when a 

 lively torpedo was placed in a small vessel 

 along with a smelt, and excited to discharge, 

 the smelt was evidently alarmed, and once or 

 twice, when exposed to the shock, leaped nearly 

 out of the vessel, but it was not injured by the 

 electricity. It has also been frequently ob- 

 served of the gymnotus that it eats very few of 

 the fishes that it kills by its discharge. 



The electrical power of the young fish is 

 proportionally very much greater than that of 

 the old, and can be exerted without exhaus- 

 tion and loss of life much more frequently. 

 After a few shocks, most of the old fish which 

 Dr. Davy has endeavoured to keep alive have 

 become languid, and died in a few hours, 

 whilst young ones, from three to six inches 

 long, remained active during ten or fifteen days, 

 and sometimes lived as many weeks. Hence 

 Dr. Davy concludes that the chief use of the 

 electrical function is to guard the fish from its 

 enemies, rather than to enable it to destroy its 

 prey, and so provide itself with food. He fur- 

 ther conjectures that, besides its defensive use, 

 the electrical function may serve also to assist 

 in respiration by effecting the decomposition of 

 the surrounding water, and so supplying the 

 gills with air when the fish is lying covered 

 with mud or sand, in which it is easy to con- 

 ceive that pure air may be deficient. And Dr. 

 Davy has often imagined that he saw something 

 of this kind going on. After repeated dis- 

 charges, he has observed, all around the margin 

 of the pectoral fins, an appearance as if very 

 minute bubbles of air were generated in it and 

 confined. That this may be one purpose 

 which the electrical function is designed to 

 serve, is rendered still more probable by the 

 circumstance, that the gills (in the torpedo at 

 least) are largely supplied with twigs of the 

 electrical nerves. In fishes in which he had 

 cut the electrical nerves, Dr. Davy found the 

 secretion of the cutaneous mucus considerably 

 diminished or altogether arrested ; and hence 

 he supposes that the electricity assists in the 

 production of this fluid. 



Lastly, it has been conjectured that the elec- 

 trical function is subservient to that of digestion. 

 This idea was started by Mr. J. Couch some 

 years ago.f He says, " Without denying that 

 the torpedo may devour that which it disables 

 by the shock, I conceive that the principal use 

 of this power has a reference to the functions of 



* Phil. Trans. 1835. 

 t Linn. Trans, xiv. 89. 



