ELECTRON

the reader should consult the article gasrs, evlrcrricaal properties of, by sir j. j. thomson, for an account of the electron and its properties. the electrons are particles whose mass is about 1/1800 part of an atorn of hvdrogen. there is only one kind of electron, for all have the same mass and carry the same electric charge. (see also elec- tricity; matter.) electrotherapy (see 9.249).-—-four different types of electricity are employed in medicine: (1) the constant, continuous or galvanic current. (2) the interrupted currents of low frequency (the interrupted galvanic current, the alternating and sinusoidal currents, the faradic current). (3) the interrupted currents of high frequency (high frequency currents, and diathermy). (4) the high voltage unidirectional currents derived from the static machine. the constant current.—it is now generally accepted that the chief curative action of the constant current is due to the reflex action resulting from the stimulation of the cutaneous and sub- cutaneous nerves immediately beneath the area over which the pads conveying the current are applied. by this reflex stimula- tion, an increased blood supply with its valuable consecutive effects is obtained. this stimulation is very similar in nature to what has been termed “ counter-irritation,” with the great advantages that the amount of stimulation is capable of exact regulation, that it takes place within the epidermis, thus acting directly on the nerve endings and that it can be continued daily for a long period, improving the condition of the skin rather than destroying it, as the constant painting on of an irritant would do. the extent of this stimulation is dependent on the strength and duration of the current employed and the nature of the solutions with which the conducting pads are moistened. when a positive pole of zinc or copper, or when salts of these metals in solution are employed, a caustic and destructive com- pound such as the chlorides or oxychlorides of zinc or copper ‘is formed in the submucous or subcutaneous area by the combina- tion of the negatively charged atoms of zinc (zinc ions), pro- ceeding from the positive pole to the tissues, with the positively charged chlorine atoms (chlorine ions) proceeding from the tissues toward the positive pole. in the process of combination the atoms get rid of their electrical charges, the process is therefore rather one of de-ionisation. this method is very valuable for the thorough and safe destruction of the diseased membranes of cavities, such as the unhealthy mucous membrane of the uterus or the lining of septic cavities. similarly, by the employment of less destructive solutions, a reflex stimulation of the tissues can be brought about. the amount of stimulation depends on (1) the nature of the solution, (2) the strength and duration of the current. in general the best results are obtained by a solution causing the minimum of irri- tation and the application of the maximum current which can be readily tolerated by the patient for at least 40 minutes. this form of treatment is indicated when increased local nutrition or the re-absorption of fibrotic thickening is desired: such as in the local treatment of chronic rheumatics, neuritis, sprains and many other conditions. it is especially valuable in the treatment of tic douloureux, for which the employment of strong currents of from 40 to 80 milliamperes is necessary. interrupted currents of low frequency.—the therapeutic effects obtainable from the employment of the interrupted currents of low frequency have been greatly increased by the methods recently introduced by prof. lapicque, prof. leduc and dr. morton smart. in the method of lapicque, by the inter- position in parallel of condensers with capacities varying from 2 to 30 micro-farads, we obtain an interrupted current of such 964 progressive onset and decline that we can excite contractions in paralysed muscles without exciting corresponding or over- powering contractions in the neighbouring healthy muscles, due to the physiological fact that the contraction excited in a par- alysed muscle is less dependent on a sharp make and break than with a healthy muscle. in the treatment of infantile paralysis objection has been raised to the electrical excitation of the paralysed muscles on account of the over-excitation of the opposing healthy muscles which accompanies such stimulation. by the method of lapicque this objection is entirely overcome. the defined and isolated contraction elicited by this method has a valuable re-educative effect in cases of recovering motor-nerve lesions. lapicque’s technique is especially useful in the treatment of facial palsy. the leduc current consists in the interruption at a frequency of about 100 per sec. of the galvanic current at the very low intensity of from two to four milliamperes. leduc claims that it is possible by employing these minute currents interrupted at such frequency to induce successively local anaesthesia and, if applied through the brain, general anaesthesia, electric sleep, coma and eventually death. applied locally, avoiding the region of the brain, this treatment is perfectly safe and has proved valuable in the treatment of certain forms of neuritis and especially in that otherwise intractable condition, causalgia. the advantages of the instrument and technique elaborated by dr. morton smart for the application of faradism to muscles deficient in excitability and tone, which have very greatly en- hanced the therapeutic value of the faradic current, are that the pain of the treatment is abolished or reduced to a minimum, the vigour and amplitude of the contractions are increased; and, above all, when employing this method, the operator can at once appreciate when the muscles are becoming fatigued and so can at once discontinue further stimulation before any of the bad elfects which were hable to occur when employing the older methods, can take place. iligh frequency currents and diathermy—although the researches of d’arsonval which led to his discovery of the high frequency currents and diathermy were commenced in 1888 and concluded in 1890, diathermy the most valuable result of his research, only began to be employed in great britain in 1911 or 1912. d’arsonval, when experimenting with alternating cur- rents in 1888, noticed that, with a constant strength of current, the more rapidly the interruptions occurred, the more vigorous were the resulting muscular contractions. when, however, a frequency of from 2,500 to 5,000 excitations a second was reached, a decrease in the vigour of the contractions occurred and progressively decreased with the increased fre- quency of excitation. at this time, the instruments at d’arson- val’s disposal did not permit a further increase of frequency, but in 1890, by employing the wireless apparatus of hertz, he ob- tained what he rather exaggeratingly termed “ billions of oscil- lations a second.”’ with these frequencies he found that he was able to pass a current of two or three amperes through the human body without producing any muscular contraction or other sensation than that of heat. he thus obtained the clinical high frequency currents. diathermic currents were subsequently evolved from the high frequency currents by such modifications in the instruments as permitted currents of lower voltage, higher amperage and higher frequency to be obtained. the main therapeutic effect of diathermy is the generation of heat deeply in the tissues by the friction from the oscillation of the electrically charged atoms. any organ of the body, any limb or part of the body, or the whole body to any extent re- quired, can be heated by this current. before the advent of diathermy we were able to heat only the superficies or the accessible cavities of the body; even under such limitations the application of heat formed one of the oldest and most useful therapeutic measures. moreover, the heat obtainable from diathermy admits of exact and easily regulated adjustment to a degree never before obtainable. the consecutive effects of heat applied in this manner are an increased blood supply, relaxation of tension and spasm with elementary education consequent relief of pain, increased local drainage, increased local nutrition. the heat thus generated is an expression of the mechanical or dynamic force excercised by the oscillations of the ions within the tissues and this primary action (the so-called “jonic massage ”’) appears to be of value in aiding the dispersal of recent effusions. some of the main indications for the appli- cation of diathermy are the relief of pain and spasm, the treat- ment of rheumatism, neuritis, sciatica, asthma and pneumonia. diathermy in surgery.—apart from its medical] application, diathermy is of considerable value in surgical practice for the destruction of superficial morbid growths, such as rodent ulcers, warts, naevi, etc. when applied for this purpose, in place of the two electrodes of large size employed in medical diathermy, one large (the indifferent electrode) and one small metal point (the active electrode) are substituted. in this way the heat, which is distributed and is only appreciated as a slight warmth over the large pad, is concentrated at the small metal point and almost immediately coagulates and destroys the tissue with which the point is brought in contact. very satisfactory results have been obtained from the treatment of haemorrhoids in this manner. the point of a metal wire can be employed as the active electrode and by inserting this wire through a cystoscope (an instrument for viewing the interior of the bladder) small growths can be readily destroyed and serious surgical operation avoided. high voltage unidirectional currents ——the therapeutic effects obtainable from the static machine were so exhaustively worked out towards the end of the roth century, notably by drs. w. j. morton and benham snow of new york, that no impor- tant developments in the use of these machines have been made in recent vears. recent research, however, has enabled the therapeutic action of the currents derived from these instruments to be rationally explained on a physiological basis and the claims formerly put forward for this form of treatment have been fully justified. (w. t.)