This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
A large number of these machines have been contrived in England, France, and Germany, as those of Newman, the Messrs. Breton, Keller, etc. The following are the essential parts of the apparatus: 1. a primary and secondary coil or helix of insulated wire; 2. a bundle of soft iron wires to be introduced within the coil; 3. a contact-breaker, by which the current is interrupted, and which is made to act through the influence of the galvanic current itself; 4. a galvanic battery or pile, consisting of one or more pairs, which is to furnish the influence by which the whole apparatus is set in operation; and 5. a pair of insulated metallic directors or conductors, which are to be connected with the poles of the apparatus, and by means of which the electricity is applied to the body. The terminations of these directors are called by M. Du-chenne excitors, and are of various character and form to meet special indications. (See page 509).
To put the machine in operation, the galvanic battery is first made to act, and the electric influence is conveyed to the ends of the larger and inner wire, which thus becomes the connecting medium between the poles of the battery. A galvanic circuit is thus established, the intensity of which is greatly increased by the reaction upon each other of the spirals through which the influence is propagated. At the same time the bundle of wires within becomes magnetized, and the outer wire acquires an induced state of great energy, and in an opposite direction to the original current. It is, however, by the frequently repeated interruption of the currents that they acquire their great physiological and remedial power, as in the electro-magnetic machine. The contact-breaker which produces this effect operates on a very simple principle. A slip of metal movable at one end, and kept in its place by a spring, is so situated that the movable end forms a part of the circuit, which passes through its point of contact. But being also near, though not in contact with the iron which becomes magnetized by the current, as soon as this is estab-lished, it is attracted by the magnetic force, and separated from its previous connection. The circuit is thus broken, the magnet loses its power, the attraction ceases, and the spring forces the movable slip back to its original position. This restores the current, and the same operation is repeated as before; so that there is a constant and rapid succession of intermissions, as long as the machine arts; the contact-breaker producing a sensible sound, as it flies rapidly backward and forward between the metallic boundaries of its movements.
The wires which serve to convey the influence of the machine to the patient, and which are of course attached to its opposite poles, are often themselves made to increase the intensity of the current, by being thrown for a portion of their length into the spiral form.
I shall not attempt to describe the various instruments employed, and must content myself here with referring the reader to a note, in the first edition of this work, in which an account is presented of one of the most recent and most perfect, which has been arranged by M. Duchenne. By consulting this account, he will be put into possession of all that will be necessary to enable him to understand and apply not only this, but other apparatuses of the same kind.*
* Excitors, or Terminations of the Directors. Before proceeding to treat of the effects of electricity on the system, it will be expedient to make a few remarks on the different modes of application, by the directors.
The form of the terminations of the free ends of the conducting wire or chain, by which the influence is conveyed to the patient, is of some importance. These terminations are called excitors by M. Duchenne. When electricity is to be applied by the aura, they should be pointed; when by sparks, rounded; when by contact, they may be of any form which the practitioner may deem most convenient; the mere touching of the excitors by any part of the surface being sufficient. Spherical, olive-shaped, or conical terminations (Fig. 2) are very common. Sometimes cylindrical pieces of metal are used, which the patient can hold in his hand. Sometimes a metallic shoe is made to fit the foot, which terminates one pole, while the other is applied to some other part of the body. The excitors may be straight or variously curved, and when to be applied by an operator, must, as before stated, have an inflating handle.
It is often necessary that the surface of the body to which they are applied should be moist, to enable the influence to penetrate through the cuticle. In such moisture. These results have been vaguely ascribed to the electrical condition of the system, and possibly with some justice; but it would be difficult to adduce positive proof of the fact; and, when we attempt to reduce the phenomena within any general rules, they quite elude our grasp.