On Miners' Nystagmus
Authors: S. Snell
Journal: BMJ (1891)

But in addition to a clhemical and thermal chanae taking place wlhen a muscle contracts, tllere is a remarkable one of aan electric character, which is supposed to be intimately con- nected with the irritability of the muscle, for it is found that these muscle curreints, as they are called, dimin-ish anld dis- appear as the irritability of the muscle decliines.Some years ago I removed a portion of a needle which had been embedded in a woman's finger upwards of two years.This piece of needle, wllich is still in my possession, was founid to be, and still remains, unattracted by an ordinary magnet, but easily attracted by a piece of steel, showing that it hals becomle magnietic.AWas it in some way rendered mag- netic through the agency of these electric muscle currents in thle living bodyIn regard to the setting free of eneray by muscular contrac- tioll, it may h)e stated broadly that the amount of contraction miiay be takein as a measure of the strengtlh and amount of nervous impulse inducing it, but that no difference can be de- tected between the nature of an impulse originating sponta- neously in tlhe central nervous system, and one excited by electric currents or mechanical stimuli.Another fact wvorthy of note is that a muscle is excited to increased action by inicreasing the work it has to do.Thus if a imusele raised a given weight to a certain height it would be inaturally thouglht tihat, if the weiglht were doubled, it would raise it to only lhalf that height, but this is not so.It is sup- posed that the stimulus of the increased weight leads to a more perfect explosion of the inogen in the muscle.Of course this is withinl limllits, for it is obvious that there must be a poinlt when 110 stimulus, hlowever great, would enable the muscle to raise tlie increased load at all.And this remark is applicable to the lheart as a muscle, for a full ventricle will {contract more vigorously thani one not so full, but an over- distended ventricl may cease to beat altogetlher.As evidenicinlg the independent irritability or sensitiveness of muscle, it may be observed tllat when the sciatic nerve is divided its irritability, owing to degenerative changes, soon disappears, but as long as six or seven wveeks afterwards there iay be muscular hlypersenisitiveness, although the mnuscle may have lost all its connection witli the nerve.Now muscular fibre, as a rule, responds like a nerve to an electric current, but it is more sluggish than nerve, and requires to be acted upon for a longer time, so that a constant current will in(luce contractionis in a muscle deprived of its nerve connection wvheln a transient induction shock will not.The condition of nerve,s supplying a muscle may be (letermined in medical practice by this test, inasmuclh as if they have nlot lost their irritability the muscle as a wlhole will respond to single induction slhocks, but if they lhave lost it the muscle will not so respond, altlhouglh it may be easily tlhrown into contractioin by the constant current.Blood supply is an important factor in mainitaining irrit- ability of botlh muscles anld nerves.Wh'lien tlle abdominal aorta is ligatured the muscles of the lower limbs lose their irritability and become rigid.So wlhen the circulation ceases, as at death, the samncX event follows in all the muscles of the body, although it slhouild be noted that rigor mortis occurs in a fixed order, beginning in the jaw and neck first, then in the muscles of the trunk, then the arms, and lastly the legs.The senise of fatigue after prolonged exertion seems, as I lhave before remarked, to be referable to tIme nervous system, and, after tIme greatest exhaustion of the muscles, recovery takes place on rest.l'erhaps notliing more rapidly produces muscular exhaustion than tetanus, and I have a distinct recollection of a case of traumatic tetanus in a young man wlhere violenit conitractions were induced by touching the wound witlh a probe, but, after a short time, exhaustion would superveine, wlhen-furthFr excitement ceased to have any effect, arid yet, on waiting some minutes, the spasm could be reproduced by the same stimulus.