Kl.KCTRICITY OF ORGANIC BEINGR 



Kl.r.rTlUCITY OF ORGANIC BKI 



> 



able to detect current* of electricity in tho muscles of animal*, by 

 cutting into them and placing one extremity of the nenre deep in the 

 wound and the other at iU lips. The experimenU of M..- 

 followed up by Du BoU-Raymond, who has arrired at the following 

 cnncliuions : 1. That galranic currenU may be observed in any liuiK 

 of any animal whether cold or warm-blooded. Theee currenU in some 

 limb* are directed downwards, in others upwards. They are of dif- 

 ferent intensity in different limb* ; but their intensity and direction 

 are always the same in the tame limb of different individuals of the 

 same species. 2. The electro-motive action on which these current* 

 depend doe* not arise from the contact of heterogeneous tissues, as 

 Volta supposed ; for the different tissues, the nerves, muscles, and 

 tendon*, in an electric point of view, are quite homogeneous. 3. These 

 currenU are produced by the muscles. If any undissected muscle of 

 any 'n'"^* 1 be brought into the circuit longitudinally, it generally 

 exhibit* an electro-motive action, the direction of which depends on 

 the poaition of the muscle. The current of the whole limb is nothing, 

 bat toe resultant of the partial cnrrenU which are engendered by 

 each muscle of the limb. It is therefore a ' muscular current.' 4. The 

 law of the muscular current may be expressed as follows : " Any point, 

 of the natural or artificial longitudinal section of the muscle is positive 

 in relation to any point of the natural or artificial transverse section." 

 5. By means of the above-mentioned law an explanation is afforded of 

 the muscular current appearing in one instance an upward one, in 

 another a downward one, which occurs according as the upper or the 

 under of the two transverse sections is made to touch one of the 

 ends of the galvanometer wire, whilst the other end is applied to the 

 longitudinal section of the muscle. This is true even as regards 

 shreds of muscle consisting of only a few primary fibres, and such as 

 only admit of observation by the microscope. 6. The nerves are 

 possessed of an electro-motive power which acts according to the same 

 law tut the muscles. Whilst still in organic connection with the 

 muscles, and forming part of a circuit in which the muscles give rise 

 to a current, the nerves simply play the part of an inactive conducting 

 body, provided their own current be prevented from entering the 

 circuit 



There are certain animals which possess the power of accumulating 

 electric force within their bodies, and of discharging it at will in n 

 violent form, and, with the exception of some insecU and Molliaca 

 which have been said (though this is doubtful) to communicate sensible 

 shocks, these animals are all included in the class of Fishes. About 

 seven species of this class, belonging to five genera, are known to 

 possess electric properties, and it is curious that these genera belong 

 to tribes very dissimilar from one another, and that, though each has 

 a limited geographical range, one species or other is found in almost 

 every part of the world. Thus, the three species of Torpedo, belong- 

 ing to the Ray tribe, are found on most of the coasts of the Atlantic 

 and Mediterranean, and sometimes so abundantly as to be a staple 

 article of food. The Gymnotiu, or Electric Eel, is confined to the 

 rivers of South America. The f-ilurtu (more correctly the Mala- 

 pttrunu), which approaches more nearly to the Salmon tribe, occurs in 

 the Niger, the Senegal, and the Nile. The Trirhiuriu, or Indian 

 Sword-Finn, is an inhabitant of the Indian Seas ; and the Tetraodon 

 (one of a genus allied to the Ltioiton, or Globe-Fish) has only been met 

 with on the coral banks of Johanna, one of the Comoro Islands. 

 These fishes have not all been examined with the same degree of 

 attention, but it seems probable that the phenomena which they 

 exhibit, and the structural peculiarities with which these are con- 

 nected, are essentially the same throughout. 



The peculiar characteristic of all is the power of giving, to any 

 living body which touches them, a shock resembling in iU effect* that 

 produced by the discharge of a Leydcn jar. This is of very variable 

 Intensity in different species and individuals, and at different times. 

 The Oymnottu will attack and paralyse horses, as well as kill small 

 animal* ; and the discharges of large fish (which are 20 feet long) 

 sometimes prove sufficient to deprive men of sense and motion. The 

 sffcoU of the contact of the Torpedo are less severe, and soon pass off; 

 bat the shock is sttended with considerable pain when the fish is 

 vigorous. The electrical organs appear to be charged and discharged 

 to a certain extent at the will of tha animals. Their power is generally 

 exerted by the approach of some other animal, or by some external 

 irriution ; but it is not always possible to call it into action, even in 

 rigorous individual*. It usually diminishes with the general feeble- 

 ness of the system, though sometimes a dying fish exerts considerable 

 power. All eUctrical fishes have their energy exhausted by a con- 

 tinued saris* of discharges ; hence it is a common practice with con- 

 voys in Sooth America to collect a number of wild horses and drive 

 them into the rivers, in order to save themselves, when they pass, 

 from being injured bv the fish. If excessively exhausted, the animals 

 may even die ; but they usually recover their electrical energy after 

 a few hoars' rest. 



The Torpedo, from iU proximity to European shores, has been most 

 frequently made the subject of observation and experiment ; and the 

 following are the most important remit* of the investigations which 

 have been made upon it by various iiii|iiin-n .That the shock 

 received by the organ* of sensation in man is really the result of an 

 electric discharge, luu now been fully established. Although no one 

 has ever teen a spark smittted from the body of one of the fish, it 



msy be easily manifested by causing the Torpedo or (fymitoliu to send 

 iU discharge through a slightly interrupted circuit The galvano- 

 meter is influenced by the discharge of the Torpedo, sn.l . !. 

 decomposition may be effected by it, as well as magnetic properties 

 communicated to needles. It seems essential to the proper re< 

 of the shock, that two parts of the body should be touched at the 

 same time, and that these two should be in different electrical states. 

 The most energetic discharge is procured from the Torpedo by touch- 

 ing the back and belly simultaneously, the electricity of the dorsal 

 surface being positive, and that of the ventral negative ; and by this 

 means the galvanometer may be strongly affected, every part of the 

 back being positive with respect to every part of the opposite surface. 

 When the two wires of the galvanometer are applied to the corre- 

 sponding parts of the two sides of the same surface, no influence is 

 manifested ; but, if the two points do not correspond in situation, 

 whether they be both on the back or both on the belly, the index of 

 toe galvanometer is made to deviate. The degree of proximity to 

 the electric organ appears to be the source of the difference in the 

 relative state of different parts of the body ; those which are near to 

 it being always positive in respect to those more distant Dr. Davy 

 found that, however much Torpedoes were irritated through a single 

 point, no discharge took place ; and he states that, when one surface 

 only is touched and irritated, the fish themselves appear to make an 

 effort to bring the border of the other surface, by muscular contrac- 

 tion, into contact with the offending body ; and that this is even done 

 by foetal fish. If a fish be placed between two plates of metal, the 

 edges of which are in contact, no shock is perceived by the hands 

 placed upon them, since the metal is a better conductor than the 

 human body ; but if the plates be separated, and while still in contact 

 with the opposite sides of the body, the hands be applied to them, 

 the discharge is at once rendered perceptible, and it may be passed 

 through a line formed by the moistened hands of two or more persons, 

 the extremities being brought into relation with the opposite plates. 

 The electrical phenomena of the llymnotut are essentially the same 

 with those of the Torpedo ; but the opposite electrical states are found 

 to exist, not between the dorsal and ventral surfaces, but between the 

 head and tail ; so that the shock is most powerful when the connec- 

 tion is formed between these two extreme points. 



It has been ascertained by experiment, that the manifestation of 

 this peculiar power depends upon the integrity of the connection 

 between the nervous centres and certain organs peculiar to electrical 

 fishes. In the Torpedo the electrical organs are of a flattened shape, 

 and occupy the front and sides of the body, forming two large masses, 

 which extend backwards and outwards from each side of the head. 

 They are composed of two layers of membrane, between which is a 

 whitish soft pulp, divided into columns by processes of the membrane 

 sent off so as to form partitions like the cells of a honeycomb ; tho 

 ends of these columns being directed towards the two surfaces of the 

 body. The columns are again subdivided horizontally by more 

 delicate partitions, which form each into a number of distinct 

 the partitions are extremely vascular, and are profusely supplied with 

 nerves, the fibres of which seem to break up into minuter lilin 

 form plexuses upon these membranes. The fluid coutmned in tho 

 electrical organs forms so large a portion of them, that the >>\ 

 gravity of the mass is only I'OM, whilst that of the body in \- 

 is about 1'060 ; and from a chemical examination of iU constituents, 

 it seems to be little else than water, holding one-tenth part of albumen 

 in solution, with a little chloride of sodium. The electrical organs of 

 (jymnottu are essentially the same in structure, though differing in 

 shape, in accordance with the conformation of the animal ; they 

 occupy one-third of its whole bulk, and run along nearly its entire 

 length ; there are however two distinct pairs, one much larger than 

 the other. The primus are here less numerous, but are much longer ; 

 for they run in the direction of the length of the body, a difference 

 which i productive of a considerable modification of the character 

 of the discharge. In the Silvrtu there is not any electrical organ so 

 definite as those just described ; but the thick layer of dense cellular 

 tissue, which completely surrounds the body, appears to be subser- 

 vient to this function ; it is composed of tendinous fibres interwoven 

 togetber,and of analbuminouasubstancuo>ntaiii<><l in tin -n- interstices, 

 so as to bear a close analogy with the cellular partitions in the special 

 organs of the Torpedo and (rymnolut. The organs of tho other known 

 electrical fishes have not yet come under the notice of any anatomist. 



In all these instances the electrical organs are supplied itli nerves 

 of very great size, larger than any others in the same animals, and 

 larger than any nerve in other animals of like bulk. They all arise in 

 the Torpedo from a ganglionic mass situated behind the cerebellum, 

 and connected with the medulla oblongata, to which the name of 

 ' electric lobe ' has been given ; the first two of them issue from the 

 cranium in close proximity with tin- fifth pair, ami have been regarded 

 as belonging to it, although their real origin is diflerent; wliiUt, from 

 the distribution of the third electrical nerve to the stomach, after 

 sending IU principal portion to the electrical organ, it would seem 

 analogous to tho eighth pair or pnoumogastric. 



The electrical nerves in the liymnoliu are believed to arise from the 

 spinal marrow alone ; ami tl. .luriu are partly intercostal* 



and partly belong to the fifth pair. The integrity of the nerves is 

 itial to the full action of the electrical organs. If all the trunks 



