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effect of electricity may be conveniently applied to test the nature of a particular nerve, as far as its motor and sensitive function is concerned; for if a current of low tension traverse a spinal nerve after the careful division of its anterior root, not the slightest motion ensues, whilst if the other root only were divided, contractions would instantly occur.

When a current is allowed to act upon the nerves of special sense, it seems simply to produce the effect of exciting their proper function. Thus if an electric current be allowed to pass from one ear to the other, a loud noise is audible; if through the eyes, flashes of light are seen; if the tongue, an acrid taste, &c. According to Grapengiesser, these results are always best noticed when the positive current enters the organ: thus on making contact, in that ear where the positive electricity enters, the loudest sound is heard, whilst on breaking connection with the battery the sound is most audible in the other ear: just what might have been expected from the observations already made on the action of cur

rents on nerves.

It must not be supposed that the feeble currents of electricity we have employed are alone active on frogs, for effects sufficiently energetic are produced by them on warm-blooded animals, and I hope to produce evidence, when speaking

of the medical application of these agents, to show that important remedial effects may be thus developed. I shall now content myself with adducing two or three recorded facts in illustration of this position.

Aldini placed a zinc plate in the mouth of a recently killed ox, and a piece of silver in the anus; on connecting them with a piece of wire, the abdominal muscles were convulsed, and a discharge of fæces occurred. This curious experiment was repeated by Achard of Berlin on himself; he experienced, almost immediately, pain in the pelvis, and soon after the contents of the bowels escaped. Humboldt tried this experiment with a linnet which was lying on its back exhausted, and in fact dying; no result occurred until the metal placed in its beak was connected with that in the cloaca, when, in an instant, the bird appeared to be resuscitated; it opened its eyes, stood up, flapped its wings, breathed for eight minutes, and then quietly died. He then tried an experiment on himself by blistering a small surface over both deltoid muscles, placing on the raw surfaces plates of zinc and silver. On connecting the metal with a conductor a distinct shock and contraction of the muscles were felt, followed soon after by others rather weaker. He also observed that the blister to which the silver was applied, soon healed up, whilst that to which

the zinc was applied discharged for a long time, and if previously nearly dry before the application of the zinc, had its discharge renewed. I shall have occasion soon to allude to some very remarkable consequences I lately observed on repeating this experiment on some patients in the wards of the hospital.

The effects produced by electricity upon the different tissues of the living body will of course vary with its intensity and quantity; for if these be at all considerable, convulsions and contractions, more or less violent, are excited in all muscular structures, whether composed of striped or plain fibres, and whether under the dominion of the will or not. These movements are accompanied by painful sensations, if the part acted upon by the electricity be supplied with nerves of sensation. If a series of powerful currents, rapidly succeeding each other, be transmitted through a limb, a state of complete tetanic convulsion is excited, accompanied, especially if the currents be alternately reversed, with sensations of intense pain. Thus, if any person, having his hands moistoned with water, grasp the conductors of the electrodynamic apparatus before me, a rapidly repeated series of alternating currents will pass through his arms, contracting the muscles so forcibly with almost tetanic rigidity, that it would be impossible to unclasp the hands and leave hold of the con

ductors. This state is accompanied by the most intensely painful sensations; so severe, indeed, that it was once soberly suggested by the contriver of one of these machines, for adoption in the army as a substitute for military flogging. If the influence of the electricity be limited to a particular muscle, contraction of that organ will alone ensue; thus, if the charge of a Leyden jar be transmitted from the scrobiculus cordis to the back, it will only influence the diaphragm, causing that muscle to contract violently, and expelling the air from the lungs with a loud shout.

When a current of electricity is made to influence the skin as exclusively as possible, great congestion of the cutaneous capillaries is produced, the surface becoming vividly reddened. If electricity of tension is employed, as by drawing large sparks from a person seated on an insulating chair, not only is this erythematous state produced, but a copious eruption of white papulæ, or rather wheals, is excited, forming indeed a good specimen of Urticaria febrilis.

103

LECTURE IV.

Medical electric Apparatus. — Common Electric Machine — Mode of exciting. Origin of Electricity in the Prime Conductor.. Positive Sparks. Insulating Chair ·

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Substitute for..

Gal

vanic Trough. - Mode of exciting. Induced Electric Currents -Mode of exciting. — Primary and Secondary Currents. Description of Electro-magnetic Machine with double Current with single Current.—Electricity of different Tensions.— Employment of Electricity at Guy's Hospital. Influence of single Pair of Plates. - Electric Moxa. — Rationale of its Action. — Treatment of indolent Ulcers.-Removal of malignant Structure. - Dr. Babington's Researches.

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I PROPOSE to-day making a few remarks regarding the forms of apparatus employed in the application of electricity and its modifications, to the treatment of disease. Of these, the common electrical machine and the electro-magnetic apparatus are the most important: by aid of the former we obtain small quantities of electricity in a state of high tension; and by the latter we obtain very large quantities of a lower tension, but still far higher than when elicited from the galvanic trough, which, indeed, is now very seldom employed for medical purposes.

You are all well acquainted with the construction of the common electrical machines; but

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