Faradizatkn.—T4e instruments employed for the exhibition of interrupted or induced currents are the magneto-electric and the electro-magnetic coil machines. In the first, the electricity is set in motion in a long thin wire coiled round a bar of iron or keeper maintained in constant whirling motion before the poles of a permanent horseshoe magnet, the magnet with every half revolution magnetizing the keeper alternately in opposite directions, while the constantly recurring magnetism of the keeper in its turn induces impulses of alternating currents in the coil-wire. The disadvantages of the magneto-electric machine, therefore, are, that it is hot self-acting, and that its currents pass alternately in opposite directions. In the electro-magnetic machine, the thick coil wire, wound over a core of iron, is made to conduct the current from a single voltaic pair which magnetizes the iron. When the battery-current is interrupted, the iron core becomes instantly demagnetized, and this change in its magnetic condition is attended with a rearrangement of the polarity of the coil-wire, and the passage through it of an impulse of induced electricity. By a simple arrangement, the magnetized iron is madeto interrupt and renew the battery-current; and the machine thus rendered self-acting, furnishes a rapid succession of momentary currents passing in the same direction, and of much greater quantity than those of the magneto-electric machine. Currents higher in tension, less in quantity, and more resembling frictional electricity, may be obtained from an additional coil (" secondary coil ") of very thin and long wire wound over the former one, but they are not of much importance in medical practice.
The physiological action of the coil-machines is equivalent to that of rapidly repeated discharges from a large Leyden jar weakly charged; and as the time engaged by the passage of each impulse in the succession of discharges is too short to permit the devel opment of any decided polarization of the tissues, the distinct calorific effects which accompany the commencement and cessation of the galvanic discharge do not occur.
The continued passage of the interrupted currents acts chiefly as a mechanical stimulant, first exciting, and after a time depressing the vitality of the part in the circuit; and its effects have been very closely imitated by vibratory impulses, produced altogether irre spective of electrical agency.
Faradization is applicable to a great variety of chronic diseases in which' a deficiency of functional energy exists; in paralytic affections unconnected with active disease of the nervous centers, mercurial and lead palsy, and in that produced by rheumatic affec tion and exposure to cold; in nervous or hysterical aphonia, or loss of voice; in amaurosis (q.v.), when not connected with inflammatory or organic disease; in nyctalo pia, or night-blindness; in amenorrhoea, when uncomplicated with active disease of the uterus; in suppression of the lacteal secretion; in constipation (q.v.) from deficiency in the peristaltic action of the intestines; in paralysis of the bladder (?), and with very doubtful effect in the induction of uterine contraction; in suspended animation from drowning, narcotic poisons, etc. In spasmodic and neuralgic diseases, the benefit of faradization is less to be depended on; but a very gentle and long-continued application of it has afforded relief in the distressing starting of the lower limbs which occurs in paraplegia or paralysis of the lower half of the body; in "writer's cramp," and spas modic forms of hysteria; in tic-douloureux, sciatica, and hysterical neuralgia. Faradi zation by electro-puncture has been successfully employed to induce the union of non-united fractures, the currents being passed between the disjoined ends of the bones; and to excite absorption in bronchocele and hydrocele, though with more doubtful effect. The intense sparks from the " secondary coil " have been used in place of those obtained by frictional electricity; and lastly, it has been proposed to employ the brilliant streams from powerful induction coils confined in fine "vacuum tubes" of glass, to illuminate internal parts of the body, for the performance of surgical opera tions, etc. '