CHAPTER III. ELECTRO-PHYSIOLOGY. I. MAGNETISM.-Of the physiological effects of magnetism little is definitely known; the north pole seems to cause irritation, the south pole sedation. II. STATIC ELECTRICITY.-1. In the electric bath the patient is placed on an insulated stool, is connected with the prime conductor by means of a chain, and is charged, positively or negatively, as desired. The electricity enters and leaves the body painlessly, slight tingling of the surface is experienced, face becomes flushed, hair erect, action of heart accelerated, and in a few moments a general perspiration breaks out. 2. Electrization by sparks.-When the body is charged as above, if we bring near a conductor (metallic knob usually), sparks can be withdrawn through the clothes; these are accompanied with burning sensations and the production of wheals. 3. In electrization by shock, the part to be acted on is placed in the circuit between the inner and outer coatings of a Leyden jar, when a severe shock is felt. 4. Motor Effects.-By a special arrangement of the static machine a so-called "static induction current" is produced; this current has the motor effects of faradism, with the advantage that it is painless. III. CURRENT ELECTRICITY. 1. Galvanic excitation of motor, sensory and mixed nerves. When a galvanic current of average strength traverses a motor nerve, a muscular contraction results only at the moment of making and breaking the circuit, and upon variations in the current strength; the amplitude of the contraction will depend upon the rapidity of the changes, and upon the pole that is placed over the nerve. Place a large electrode over the sternum or some other indifferent point; then with a small one over a motor nerve or muscle ascertain the minimum current strength necessary to produce a contraction upon closing (C) and opening (O) the circuit, first with the kathode (K), then with the anode (A). The increase of current strength necessary will be found to occur in a regular order known as the normal polar formula, and is as follows: 1. Weak current.... 3. Strong current........ ...KCC ACC AOC .KOC The contractions resulting from sudden reversals of polarity by means of the commutator are known as voltaic alternatives, and are much more powerful than those resulting from simple makes and breaks. During closure the excitability of the nerve is diminished at the point of contact with the anode, (anelectrotonos), increased at the kathode (katelectrotonos), so that excitation of the nerve results from AO., i.e., the return to normal from anelectrotonos, and from KC., i.e., the production of katelectrotonos. Excitation upon closure really only occurs at the kathode; upon opening only at the anode, KOC and ACC being accounted for on the theory of virtual electrodes, which cannot be discussed here. Watteville.) (See De Nothing is gained by placing both poles over the nerve, for the current proceeds in all directions from the electrode, and at a short distance the nerve is practically devoid of current. This diffusion of the current gives rise to "induced contractions" in neighboring muscles. Pain results from excitation of a sensitive nerve, even when the current flows continuously, and is felt both at the point of application and in its peripheral distribution. In mixed nerves the effects are pain and muscular contractions. 2. Faradic excitation of motor, sensory and mixed nerves.-When a slowly interrupted faradic current traverses a motor nerve, a muscular contraction occurs at each break, but if the interrupter vibrates rapidly the contraction becomes tetanic. Similar stimulation of a sensitive nerve causes pain, and of a mixed nerve pain and motion. The effect of galvanism when applied directly to muscle is the same as that resulting from stimulation of its motor nerve, but the short duration currents of faradism do not so readily affect it; indeed, the contractions from faradism are probably due to stimulation of the intra-muscular nerve elements. The reactions to both currents are more powerful by direct stimulation, in which the electrode is placed over the |