the conductors are applied to any part of the face. A moistened rheophore is applied to the closed eye and a second to any part of the face.

Electrization of the auditory nerve.-The external auditory meatus is filled with tepid water, and a metallic rheophore, insulated by ivory or vulcanite, is placed in it, and the circuit completed by a moist rheophore on the neck. The operation is shown in fig. 43.

Electrization of the olfactory nerves.-A moist rheophore is placed over the back of the neck, and a metal sound, insulated except at its extremity, is moved over all points of the nasal mucous membrane.

Electrization of the nerves of taste.-A rheophore is placed over the back of the neck, and a second is moved over the base and borders of the tongue.

CHAPTER III.

ELECTRICITY AS AN AID TO DIAGNOSIS.

ELECTRICITY will assist us in diagnosis only in those conditions in which there is altered muscular contractility, or cutaneous or muscular sensibility, or both. In the normal and healthy state of this tissue muscles and nerves respond to the electric stimulus whatever variety of electricity is employed, but in disease this reaction may be increased or diminished or altogether absent. The irritability of a muscle is tested by ascertaining the lowest power which will cause its contraction. The procedure is as follows: Assume the case, for example, to be one of ordinary hemiplegia, say of the left side. Take in one hand the two rheophores of a Faradic instrument in action and apply them to one of the muscles the extensor communis digitorum will do— of the right or healthy side; having found the lowest power to which the muscle responds, apply the rheophores to the same points of the same muscle on the diseased side, and note whether there is contraction; if there is, decrease the power of the current, and if contraction still occurs there is increased irritability, or vice versâ, as the case may be. In testing with the voltaic current keep one electrode stationary and

interrupt the current by gliding the second over the muscle or repeatedly lifting and re-applying it. It is essential that on both sides there should be exact similarity in the application, and that the electrodes should be placed on identical points of the muscle; and this is especially important with the voltaic current, for healthy muscles answer to it more readily when it flows down the limb than when it flows up, and consequently a reversal of the poles will influence the result.* In testing a case of paraplegia where there is equal disease on both sides, you must be guided by a knowledge of the strength of current usually required to bring about contraction. As a general rule, unless a current that causes energetic and painful action in the muscles of the ball of the thumb produce some contraction the irritability is impaired. In either diagnostic or therapeutic electrization the operator should never use electricity upon a patient without first testing it upon his own hand, and if about to apply it to the face, upon his own face. This is a most important rule, never to be neglected. There is no certain means of securing that the strength of either a voltaic or faradic current shall not have

* The current that passes from a nerve centre to the periphery, that is, from the positive electrode placed nearer to the centre, to the negative, placed farther from it, is called a "direct" or descending current. The reverse current is the "indirect" or ascending. Healthy nerve and muscle respond to a lower power when the current is descending than when it is ascending.

varied from day to day, and unless we get into the habit of trusting to our own muscles for fine degrees of graduation we shall often be foiled in our object. In a case of hemiplegia it will be found probably that the irritability to both varieties of electricity is normal. This proves the integrity of the muscular tissue. If the muscle also responds to indirect excitation by its motor nerves, we know in addition that the conducting power of the nerves is uninjured, and that the spinal cord has preserved its integrity at the spot where the nerves are given off. The disease is in the brain. But we may find the irritability somewhat diminished. This in hemiplegia will probably be from disuse and a few faradizations will restore it; if not, there is disease of cord or nerve or muscular tissue, and the disease, as a rule, will be in direct proportion to the amount of diminished irritability. But on the contrary, the irritability may be increased when there is often some rigidity. This points to increased vascularity, irritative lesion of brain or cord, or both.

Test now with the interrupted voltaic current. As a rule its reaction will correspond with that of faradism, but in some cases in which response to faradism is diminished or abolished, the reaction to a slowly interrupted voltaic current is not only preserved but greatly increased. On the diseased side the muscles will respond much more readily to the voltaic current than on the healthy side. When this reaction exists,

that to faradism being lost, it has been shown that the nerves also do not react to faradism, and that the increased irritability is due to the Hallerian irritability inherent in muscular tissue; but why this should be increased over that existing in healthy muscle has not yet been shown. Ziemssen reports a case of purely traumatic facial paralysis produced by a surgical operation in which the trunk of the facial nerve was completely divided. At the end of three weeks the excitability of the motor nerves to faradism and voltaism was lost. The paralysed muscles on the contrary had preserved their irritability to the interrupted voltaic current and responded by a slow contraction, due to the muscular tissue without the agency of nerve.

This muscular reaction to the slowly interrupted voltaic current is often of great use in the diagnosis of peripheral from central paralysis (e.g., in the diagnosis of paralysis of the facial nerve from facial hemiplegia.) Reaction of this kind exists only in peripheral, never in central lesion. In peripheral paralysis there is, in addition, loss of farado-contractility. Observing this in a case of paralysis of the muscles of the shoulder, Duchenne diagnosed local nerve-lesion, and a syphilitic exostosis was afterwards found compressing the nerves. By this same differential reaction it may be determined whether, in a case of paralysis of the extensors of the wrist and fingers, the paralysis is due to the impreg