Animal near the spine, and attached to its muscles and to the Electricity, air-bladder above, and separated into a right and left organ by a septum. The other pair, which is much smaller, is beneath the former. The space separating the right from the left is occupied by the muscles which move the long abdominal fin. These organs consist of numerous membranes, lying horizontally over one another, and connected by numerous septa. They are supplied with numerous nerves of great magnitude, both from the spinal cord and the great sympathetics. The shocks communicated by this animal are much stronger than those which the torpedo gives, so that it is impossible, on account of their violence, to extend our knowledge of the physiology of the animal by handling it freely in its living state. It communicates at pleasure a shock to an animal at a short distance from it in the water. This is its first object in securing its prey. It swims up near to a fish, looks at it, then conveys to it a shock, which either instantly kills it, or stuns it so that it is deprived of all voluntary motion. When its end is not fully accomplished, it gives a second and stronger shock; very often it kills in this manner fishes which are larger than itself, and which it either cannot or will not eat. This shock is proved to be as decidedly electrical as that of the raia torpedo. The particulars of the experiments made by Dr Williamson, and also an anatomical account of it by Mr John Hunter, with large plates, are contained in the 65th volume of the Philosophical Transactions. 543 The silurus A third electrical fish, is the silurus electricus, which electrieus differs in the situation and form of its peculiar organs from both of the two preceding. These organs form a universal envelope over the body, immediately under the skin. They consist of a collection of cellular tissue, so compact, that it might at first view be considered as a stratum of fat; but, when minutely examined, it is found to consist of tendinous fibres, forming a reticulation, the meshes of which require the aid of a magnifying power to distinguish them: these are filled with a gelatinous substance. Thus it appears, that neither the situation of the electric organs, nor the form of the cells, is to be considered as constant in animals of this description. It is also discovered, by anatomical examination, that no branch of the nervous system is particularly set apart for this set of organs, as the nerves sent to it are different in all the species. The essential circumstances are, multiplied aponeuro ses, with extensive surfaces, forming numerous cells, Animal and these cells filled with gelatinous matter, and sup- Electricity. plied with nerves of great size and length. Other spe cies of rays, besides the torpedo, have a collection of gelatine, in a part of the body corresponding to the electric organ of the raia torpedo; but it is not separated into numerous minute portions by close aponeurotic cells. It lies in large continuous quantities, in lengthened cavities, communicating with the surface by open orifices; and hence the nerves distributed to it, though of considerable size, are incapable of eliciting from it any electrical phenomena. Other two fishes are known to possess a similar power, viz. the trichiurus indicus, and the tetraodon electricus, both found in the Indian seas: but we know nothing of the distinguishing characters of their electric organs. 544 Electrical phenomena, occasionally developed by Electricity other animals, and also by the human body, have been of the hu recorded by naturalists and historians, both ancient and man body. modern. In some individuals it has been excited by stroking their own hair backwards, or by combing. Some people have habitually observed electrical light to be given out when their shirts were moved. This has occasionally been remarked to occur in cases of disease, such as consumption. It has been further observed that, besides these palpable appearances of occasional occurrence, others are capable of being regularly produced by motion of the body, provided the clothes are of the same temperature with the body itself, and there is no perspiration present. This electricity is made apparent by the condenser, when it has been excited while the body was insulated. A quantity is present, independently of motion. It is different in degree in different persons. It differs in kind on different occasions, and even varies in this respect in the course of one experiment. On the whole, however, it is naturally positive. When it is negative, the body is in an unnatural state. Cold weakens it, or reduces it to zero, or changes it to the negative form. Lassitude has a similar operation. Sudden and violent motion changes every kind of animal electricity to the opposite. Continual straining of the thoughts is favourable to positive electricity. The breath has no effect on it, and does not sensibly conduct it. Such are the leading results made on this subject by the delicate experi ments of Mr Hemmer, an account of which is contained in the 5th volume of the Philosophical Magazine. PART VIII. APPLICATION OF ELECTRICITY TO MEDICINE. AT one time, the powers of electricity over the animal economy, were represented by some persons in Italy as so remarkable, that a suspicion of exaggeration and fable was naturally excited. It was asserted, that by means of the electrical shock, the virtues of medicinal drugs held in the hand were diffused through the whole body. The abbé Nollet and others exposed, by a set of careful experiments, the imposture of these pretensions, in a visit which they paid to Italy for the VOL. VII. Part II. + 545 express purpose of investigating the subject. Other similar frauds have been practised upon this subject, which it would serve no purpose to describe. But Mode of there can be no doubt, that the application of electri- applying it city bas, in many instances of disease, proved useful. to medical Shocks may be communicated in quick succession, and uses. of a regulated strength, by means of a Leyden jar fitted up with Lane's electrometer. Two directors of metal are employed, with a metallic ball at one end of 5 K each, Opacity of the cornea is sometimes cured by electri- Medical Suppressed menstruation has been relieved, but not In a few cases of pain and swelling of the knee, re- In chronic rheumatism the success is very fre- Chorea has been frequently relieved; palsy occa- It must, however, be remarked, that the indiscrimi- amusement. |