CHAMBERS'S INFORMATION FOR THE PEOPLE. 



between the pectoral fins, the head, and gills. 

 Each battery consists of a number (varying 

 according to age) of hexagonal prisms, some- 

 what like the cells of a honeycomb. The double 

 set of organs is completely under the control of 

 the torpedo ; it can give a shock similar to 

 that of a Leyden jar ; and Matteucci has even 

 obtained sparks from it. 



Among other kinds of fish with a similar power, 

 the most noted is the Gymnotus electricus, or 

 electrical eel, found in the rivers of Bengal and 

 Surinam, and common in all the streams flowing 

 into the Orinoco. It is from three to four feet in 

 length usually, though it has been found even six 

 feet long. The whole of its viscera and digestive 

 organs lie near the head, the rest of the body 

 being taken up with the electrical apparatus. This 

 consists of four batteries two on each side, and 

 placed one above the other, the upper being the 

 larger. The batteries are made up of a number 

 of piles, looking very like galvanic troughs, and 

 numbering from thirty to sixty in the upper, and 

 from eight to fourteen in the lower battery. 



Faraday experimented, about 1840, on a speci- 

 men of this eel, exhibited in the Adelaide Gallery, 

 in London. The shock which the animal was 

 capable of giving was very great, equal to that of 

 a good-sized Leyden battery. It was strongest 

 when one hand communicated with the head, and 

 the other with the tail, and it was sufficient to stun 

 or even kill fish. 



In all such cases we have the extreme of electric 

 development in the animal system. But apart 

 from special organs, living nerve and muscle have 

 an electricity of their own, which fails as life dies 

 out, and is wanting altogether after death. Much 

 attention has been given of late years to this 

 electricity of muscles and nerves ; and the dis- 

 coveries of Du Bois-Reymond, Matteucci, and 

 others, have given the study a title to be regarded 

 as a branch of physical science. 



Galvani must, however, be credited with being 

 the father of the science. Frog-limbs, as prepared 

 by him, are still one of the best means of shewing 

 not only the effect of galvanic action on the animal 

 frame, but also the existence of an electro-motive 

 force in the frame itself. Galvani proved that two 

 metals in contact are not required to cause con- 

 vulsions in the frog-limbs. A single wire joining 

 the spinal nerves with the muscles of the leg 

 causes sensible convulsions, and he argued from 

 this the existence of muscular and nervous 

 currents. 



The existence and principal laws of such cur- 

 rents are now beyond a doubt ; but we are still in 

 darkness as to their real origin, and their analogy 

 to other known sources of electricity. 



In living animals, or in those very recently 

 killed, there is always a current flowing from the 

 interior of a muscle or of a nerve to its surface. 

 These currents cease in warm-blooded animals in 

 a few minutes after death ; but in cold-blooded 

 animals, such as the frog, they continue for a 

 much longer period. 



That there are natural electricities resident in 

 the nerves and muscles to cause these currents, 

 may be shewn by a delicate galvanometer, or by 

 the quadrant electrometer of Sir W. Thomson, i 

 By means of this sensitive electrometer, it is ] 

 found that the surfaces and the ends of nerve (or i 

 muscle) fibres are oppositely charged like the two 



286 



coatings of a Leyden jar. The sheaths of the 

 fibres are supposed to be such bad conductors 

 that they can act as a dielectric, like the glass of 

 the Leyden jar. A charge is given to the outer 

 surface by oxygenation, or in some other way, and 

 an opposite charge is induced by it on the inside. 

 The current that affects the galvanometer arises 

 from the connecting two oppositely charged parts. 



But the curious thing is, that the muscle and 

 nerve fibres are charged, while they remain at 

 rest, and action is accompanied with a disappear- 

 ance or discharge of the electricities. This is like 

 the discharge which occurs when the torpedo puts 

 itself in action. Indeed, the discharge of the 

 torpedo may only be ' the unmasked form of what 

 occurs in a masked form in every case of muscular 

 and nervous action.' 



As, then, a natural activity of nerve and muscle 

 coincides with natural electric discharges in their 

 tissues, so an artificial activity is induced by arti- 

 ficial discharges. Mere charge or electrification 

 has no effect, so long as it is constant. It is only 

 a. sudden change of charge (which is really a dis- 

 charge) that produces an involuntary and arti- 

 ficial activity. 



This explains why the passage of a voltaic 

 current is attended with no artificial production of 

 action so long as it is constant. It is just equiv- 

 alent to a constant charge of the fibres, and, there- 

 fore, to a state of rest. Only at the letting on or 

 taking off of this charge do we have a change of 

 state, which is really a discharge ; only then do 

 we feel the shock ; and only then are the fibres 

 excited. This is easily verified by experiment 

 with the galvanic current, either on the living 

 body, or on the bodies of animals recently dead. 



The physiological effects of electricity were 

 among the first observed, and had doubtless a 

 good deal to do with the rapid development of 

 the science. The life-like convulsions excited by 

 it in the limbs of dead animals hinted that nerve- 

 force might be nothing but electricity. Many 

 experiments were made on the bodies of oxen, 

 horses, sheep, and such like, soon after death. 

 Executed criminals were even experimented on, 

 and many of the vital actions were alarmingly 

 induced. All this was to find the connection 

 between vital and electrical force. It was clear 

 there was some relation, and it was thought 

 probable that the two forces might be identical. 



Experiment has, however, failed to establish 

 any relation between electricity and life, so definite 

 as it has established between electricity and the 

 physical forces of heat, light, chemical, magneti- 

 cal, and mechanical force. Man would fain find 

 out the secret of life, and the panacea for all his 

 infirmities. But the problem remains, and will 

 remain, unsolved. 



HISTORICAL SKETCH. 



Magnetism. All that the ancients knew of 

 magnetism was the property of the loadstone. 

 Even the compass is comparatively modern. We 

 are not sure of its being known in Europe before 

 the end of the twelfth century, though some say 

 the Chinese had it long before. Columbus, on 

 his famous voyage, first noticed the variation of 

 the compass; and about eighty years after (1576), 

 a London instrument-maker discovered the dip. 

 In the beginning of the seventeenth century, 



