Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/essentialsofmediOOmortrich ESSENTIALS OF MEDICAL ELECTRICITY A TEXT/BOOK OF RADIOLOGY BY E. REGINALD MORTON M.D., CM. (tRIN. tor.), F.R.C.S. (EDIN.) Past President, Section of Electro-Therapeutics, Royal Society of Medicine, Lecturer on Radi- ology, West London Post Graduate College, in charge of X-Ray Department, West London Hospital, etc., etc. Demy octavo. 237 pages. 26 full-page plates and 72 illustrations. Cloth "Eminently practical and up-to-date." — Archives of the Roentgen Ray. "A very valuable addition." — Lancet. "Should be on the bookshelf of every naval medical o^c&r." ^Journal oj the Royal Naval Medical Service. "This is an eminently practical book." — Indian Medical Record. "It is most concise, beautifully illustrated, and abounding with useful information." — Edinburgh Medical Journal. "It is the book of all others to be recom- mended." — Universal Medical Record. " We can heartily recommend it as a most useful guide and a valuable addition to X-ray literature." — West London Medical Journal. ESSENTIALS OF MEDICAL ELECTRICITY BY E. REGINALD MORTON M.D. (trin. tor.), F.R.C.S. (edin.) Medical Officer in Charge, X-Bay Department, West London Hospital, etc. THIRD EDITION, REVISED AND REWRITTEN WITH ADDITION OF NEW MATTER BY ELKIN P. CUIVIBERBATCH, m.a., m.b., b.ch., oxon. Member of the Boyal College of Physicians of London, Medical Officer in Charge of the Electrical Department, St. Bartholomew's Hospital, and late Demor^strator of Physiology in the Medical Scnool^ WITH ELEVEN PLATES AND SEVENTY-TWO ILLUSTRATIONS ST. LOUIS C. V. MOSBY COMPANY 1916 ^ .^^^; .^ \p y> / PREFACE TO THE THIRD EDITION Since the appearance of the last edition of the present work considerable advances have been made in the subject of medical electricity. New and important methods have been introduced, while the mode of action of electricity in the treatment of disease is now more clearly understood. The author of the present edition has therefore found it necessary to rewrite and rearrange the work so as to include the new methods and, at the same time, present the subject in the light of the newer and clearer know- ledge of the way in which electricity acts in the cure or relief of disease. The different methods of electrical treatment have been considered in separate chapters. The title of the book compels the insertion of a chapter dealing with the elementary physical principles of electricity, for know- ledge of the latter is essential for the successful practice of electro -therapy. The chapter deaHng with this part of the subject has been placed at the end of the book, so that those who have not forgotten the elements of the physics of electricity can commence, as soon as possible, the chapters dealing with the application of electricity for medical purposes. E. P. C. 15 Upper Wimpole Streist, W. 1916. 380586 CONTENTS PAGE Introduction .... i CHAPTER I The Mode of Action of Electricity on the Body ..... 3-15 CHAPTER II The Constant Current and its Modifica- tions ..... 16-34 Constant Current — Simple Interrupted Current — Simple Alternating Current — Sinusoidal Current — Slow Sinusoidal Currents — Faradic Current CHAPTER III Sources of Electrical vSupply . . 35-63 Current from the Main — Direct Current — Alternating Current — Rectifiers — Dangers attending Use of Main Current — Private I nstallation — Accumulators — Prim- ary Batteries — Dry Cells CHAPTER IV The Body as a Conductor of Electricity . 64-70 Resistance of the Body — Path of Current — Anode and Kathode — Conduction of Ciurrents at High Voltage CHAPTER V Ionic Medication .... 71-87 Definition — Introduction of Ions into Body — ^Advan- tages — Limitations — Penetration — Apparatus — Source of Current— Ions used — Practical Application — lonisation of Special Parts — Duration of Treatment yii viii CONTENTS CHAPTER VI PAGE Surgical Ionisation — The Use of the Electrical Current for Destruction of Tissue ..... 88-98 Principles — Removal of Superfluous Hairs — Nsevi — Monopolar Method — Bipolar Method — Stellate Veins — Warts — Moles — Strictures of Urethra — Uterine Fibromyomata — Aneurysm — Malignant Growths CHAPTER VII Ionisation in Deep-Lying Tissues . . 99-103 CHAPTER VIII The Use of the Electrical Current for Stimulation of the Tissues ; Electric Baths . . . . . 104-117 Modification of Current for Stimulation of Tissues — Application to the Body — Electric Baths — General Faradisation or Galvanisation CHAPTER IX Electrical Treatment of Paralysis . 118-137 Current — Electrodes — Strength and Duration of Treatment — Peripheral Nerve Paralysis — Facial Paralysis — Paralysis of Shoulder Muscles — Of Arm Muscles — Erb's Paralysis — Peripheral Nerve Paralysis in Lower Limb — Infantile Paralysis CHAPTER X The Use of the Electrical Current for Testing the Reactions of Muscle and Nerve ..... 138-160 Normal Muscle and Nerve — How Electrical Testing is carried out — Testing Nerve Trunks — Types of Re- action — Meaning of Various Reactions — Course of the Reaction of Degeneration — Prognosis — Practical Diffi- culties — Defects — Testing with Condenser Discharges CONTENTS ix CHAPTER XI PAGE High-Frequency Currents . . 161-177 How Currents are produced — Apparatus — Measure- ment — How applied — Action — High-Frequency and Surgical Cases CHAPTER XII Diathermy ..... 178-193 Production of Currents — Physiological Action — Proof of Heating of Deep Parts — How applied — Medical Diathermy — Surgical Diathermy — How performed — Advantages — Results CHAPTER XIII The Use of Static Electricity . . 194-213 Apparatus — Machines — Accessory Apparatus — Machine in Action — Methods of Application — Static Bath — Static Wave Current — Static Breeze — Electrical Sparks — Static Induced Current CHAPTER XIV Index of Electrical Treatment . . 214-251 Acne — Acroparaesthesia — Alopecia — Amenorrhoea — Anal Fissure — Aneurysm — Aphonia — Arthritis — Anterior Poliomyelitis — Asthma — Boils — Car- buncles — Cardiac Failure — Chilblains — Chorea — Colitis — Congestion — Constipation — Corns — Corneal Ulcers — Corneal Opacities — Disorders of Digestion — Disseminated Sclerosis — Dupuytren's Contraction — Dysmenorrhoea — Endometritis — Episcleritis — Exophthalmic Goitre — Fibrositis — Fistula — Gonorrhoea — Headache — Hemiplegia — High Blood Pressure — H5rpertrichosis — Hysteria — Incontinence of Urine — Ingrowing Eyelashes — In- somnia — Intermittent Claudication — Keratitis — Lachrymal Obstruction — Locomotor Ataxy — Lupus — Malignant Growths — Mental Diseases — Meralgia Paraesthetica — Metatarsalgia — Moles — Myalgia — Myelitis — Naevus — Neuralgia — Neurasthenia — X CONTENTS Chapter XIV — continued PAGE Neuritis — Obesity — (Esophageal Spasm — Orchitis — Ophthalmia Neonatorum — Optic Neuritis — Ovarian Neuralgia — Ozaena — Paralysis — Paralysis Agitans — Perineuritis — Piles — Pleurisy — Port- Wine Marks — Prostatic Enlargement — Pruritus — Pyorrhoea Alveolaris — Raynaud's Disease — Rickets — Rodent Ulcer — Scars — Sciatica — Sexual Disorders — Sinuses — Spring Catarrh — Sycosis — Synovitis — Tinea Tonsurans — Tinnitus Aurium — Trachoma — Ulcers — Variocele — Varicose Veins — Writer's Cramp — Warts CHAPTER XV Physical Principles . . . 252-295 Nature of Electricity — Static Electricity — Conductors and Insulators — Induction — Electroscope — Density — Capacity — Condensers — Production of Static Electricity — Current Electricity — Chemical Methods — Voltaic Cell — Dry Cells — Accumulators — Bi- chromate Batteries — IVIeasurement — Electro-motive Force — Resistance — Unit of Current — Ohm's Law — Internal Resistance — Arrangement of Cells — Current Density — Magnetism — Galvanometer — Electro-magnet — Electro-magnetic Induction — Self-induction — Alternating Current — Dynamo — Motor Transformers — Static Transformer LIST OF ILLUSTRATIONS PAGE Plates L-XI. — Motor points and cutaneous areas .... Facing page i6o FIG. 1. Passage of current through a solution of sodium chloride . . . . .5 2. Passage of current through a solution of sodium chloride . . . . .7 3. Graphic representation of Simple Interrupted Current . . . . • ^7 4. Metronome Interrupter. Baird & Tatlock . 18 5. Plan of Commutator of Leduc . . 19 6. Leduc's Mechanical Interrupter. Newton & Wright . . . . .20 7. Ruhmkorff's Commutator . . .21 8. Graphic representation of a Simple Alternating Current . . . . . 22 9. Graphic representation of a Sinusoidal Current 23 10. Pantostat. Schall & Son . . .24 11. Plan of Ewing's Rhythmic Reverser . . 26 12. Diagram of Primary Circuit of induction coil . 28 13. Graphic record of the Primary and Secondary Currents of an induction coil. H. K. Lewis &Co. . . . . • 30 14. Graphic record of the Secondary Current. H. K. Lewis & Co. . . . -31 15. Lewis Jones' Coil. Schall & Son . '32 16. Sledge Coil. Schall & Son . • • 33 xii LIST OF ILLUSTRATIONS FIG. PAGE 17. Current derived from main . . -36 18. Plan of Shunt Resistance. Schall & Son . 37 19. Shimt Resistance. Schall & Son . . 39 20. Morton Box. Schall & Son . . .40 21. Galvano-faradic Outfit. Schall & Son . 41 22. Shunt Resistance for Cautery. Schall & Son 43 23. Scheme for derivation of current from alternat- ing current by way of a transformer . 47 24. Transformer for Light and Cautery. Schall & Son . . . .48 25. Plan showing how shocks maybe accidentally derived from main current . . -53 26. Plan showing how shocks may be accidentally derived from main current . . -55 27. Portable Dry Cell Battery. Cavendish Electrical Co. ..... 61 28. Double Crank Collector. Schall & Son . 62 29. Diagram to indicate divergent lines of flow of constant current through tissues . 66 30. Diffusion of current . . . -67 31. Diffusion of current . . . .68 32. Anode overlying muscle under skin . . 69 33. Diagram of Electrode . . -7^ 34. Epilation Needle fixed to Holder. Schall & Son 90 35. Needles for Electrolysis. Schall & Son . 91 36. Lewis Jones' Bi-polar Needle. Schall & Son . 92 37. Bougie Electrode. Schall & Son . . 95 38. Rhythmic Resistance- varying Device. Watson & Sons ..... 107 39. Rhythmic Resistance- varying Device. Schall & Son ..... 108 40. Schnee Bath , . . . '113 LIST OF ILLUSTRATIONS xiii FIG. ■ PAGE 41. Paddle Electrode. Schall & Son . .114 42. Combined Battery. Schall & Son . . 140 43. Testing Electrode. Cavendish Electrical Co. . 141 44. D'Arsonval's Transformer. Schall & Son . 162 45. Plan of High-Frequency Arrangement . 163 46. Intermittent trains of oscillations . . 165 47. Hot-wire Milliampere-meter. Schall & Son . 166 48. High-Frequency Outfit. Schall & Son . 167 49. Auto-Condensation Couch. Watson & Sons . 169 50. Vacuum Electrodes. Cossor . . 172 51. Diagram showing circuits in a diathermy apparatus . . . . .180 52. Diathermy Machine. A. E. Dean . .182 53. Condenser Couch. Schall & Son . .186 54. Wimshurst Machine. Newton & Wright . 195 55. Holtz Machine. Whittaker S- Co. . . 198 56. Electrodes for use with Static Machine . 201 57. Static Breeze ..... 204 58. Arrangement of Apparatus for application of Static Wave Current . . . 206 59. Arrangement of Apparatus for application of Static Breeze .... 209 60. Arrangement of Apparatus for application of Static Induced Current . . . .212 61. Electrode for Enuresis . . . 230 62. Electroscope . . . . .258 63. Leyden Jar. Newton cS^ Wright , . 262 64. Plates and Poles of a Voltaic Cell . . 267 65. Diagram of Twelve Cells joined in Series . 278 66. Diagram of Twelve Cells joined in Parallel . 279 67. Lines of Force around a Bar Magnet . . 282 xiv LIST OF ILLUSTRATIONS FIG. 68. Milliampere-meter of the "Moving Coil" Type. Cavendish Electrical Co. . . .264 69. Arrangement of Shunts in Milliampere-meter. Schall &' Son . . . .285 70. To illustrate way in which an Alternating Sinusoidal Current is produced . . 289 71. Dynamo constructed to generate a Direct Current. General Electric Co. . .291 72. Plan of a Static Transformer . . 294 Essentials of Medical Electricity INTRODUCTION The subject of the present volume is the use of electric- ity for the treatment of disease. Although the precise nature of electricity is unknown, its mode of action on the body is now more clearly understood, and it is being gradually recognised that its physiological and thera- peutic effects are the consequence either of chemical or physical changes that it brings about in the tissues. The nature of these chemical and physical changes will be set forth in Chapter I. In many cases it is quite clear how electricity, by bringing about these changes, can cure disease or relieve its symptoms ; in others it is less evident ; but so long as we look upon the unknown agent electricity as an agent which produces known chemical and physical effects, we are enabled to see more clearly which diseases and morbid conditions are likely to benefit and render less empirical their electrical treatment. For the practice of medicaL electricity a sound know- ledge of physics is necessary, for, without it, the principles of the subject and even the meaning of the terms in everyday use will not be understood, and it will be im- possible to discover and put right simple failures of the apparatus when they occur. Those whose knowledge of physics has grown grey will find a brief outline of the physical principles of electricity and explanations of the terms in common use in Chapter XV. A I 2 .- ; KSSENTIAL? or MEDICAL ELECTRICITY With the exception of its use in testing the reactions of muscle and nerve, electricity deals almost entirely with treatment. Of the maladies for which it is used, there are some for which it procures cure or relief where other methods have failed, or where other methods are slower and less efficacious. There are other maladies, incurable by any known method, for which electrical treatment is still sometimes requested, cases which drift down, like derehcts, to the electrical departments of hospitals on the chance that some benefit may be derived there. There is a third group of maladies comprising the diseases of which the symptoms can be relieved by electrical treatment. For these, electricity is part of the treatment of the disease, and if it is to 3deld the best results the general treatment should not be neglected. There is, now, no region of the body to which electrical treatment is not apphed, and it is essential that the practitioner of electro-therapeutics should have a general experience of medicine as well as a special knowledge of the subject dealt with in the present book, while the prescriber should be acquainted with the field of medical electricity, so that the treatment may be administered only to suitable cases. CHAPTER I THE MODE OF ACTION OF ELECTRICITY ON THE BODY It has been mentioned in the Introduction that the physiological and therapeutic action of electricity is due to chemical or physical changes which it produces in the tissues. The way in which these changes are brought about will be best understood by the study of the pass- age of an electric current through water containing a salt in solution. If two wires leading from the poles of a battery are immersed in water without touching, and a milliampere-meter is placed in circuit, no current will be indicated if the water is perfectly purp and contains no salts in solution. The needle of the milli- ampere-meter wiU remain at zero. If now a salt such as sodiimi chloride is dissolved in the water, the current is able to flow and the needle of the milliampere-meter moves across the scale. The addition of any other salt will produce the same effect, provided it is soluble in water. So also will a soluble base (such as sodiimi hydrate) or a soluble acid. These bodies, when dis- solved, form solutions that enable the current to flow, and are known as "electrolytes." In the dry, undis- solved condition they do not conduct the electrical current any more than the pure water, but in solution they undergo change, so that the current is able to pass. If, instead of a salt or base or acid, some albumen or other soluble protein, free from salts, is dissolved in pure water, no current will flow. If starch or dextrine or dextrose is dissolved, still no current wiU flow. Pro- teins and carbohydrates, and other chemicals such as 3 4 ESSENTIALS OF MEDICAL ELECTRICITY alcohol and phenol do not, when they pass into solution, enable the electric current to pass : they are not electro- lytes. The first important point to be observed with regard to the passage of the electric current through the body is this — ^the tissues conduct the electric current because they contain electrolytes — viz. salts in solution. The tissue protoplasm and its products are not them- selves conductors of this current, but the latter can pass through them because they are permeated with fluid that contains salts in solution. To return to the experiment on the passage of the current through the solution of salt. The passage of the current is not the only phenomenon observed. Chemical changes are at the same time taking place. One of these is evident. Bubbles of gas (hydrogen) are seen escaping in the region where the current is leaving the solution. Other chemical changes are taking place at the same time and will be. mentioned in due course. It is now necessary to consider more in detail the nature of these chemical changes and how they are brought about. When an electrol5d;e dissolves in water (thereby enabling the current to pass) it undergoes certain changes. It is generally believed that in the process of solution a certain proportion of the molecules divide or dissociate into two parts, each part taking an electrical change. These electrically charged parts are known as " ions." Thus when a molecule of sodium chloride dissolves in water it divides into two parts, one, + the sodium ion, bearing a positive charge (Na), the other, the chlorine ion, bearing a negative charge (CI). The ions have properties quite different from those of the un- electrified atoms. A solution of sodium chloride contains sodium ions, and chlorine ions, and in addition undivided molecules of sodium chlorides. The ions take no particular course, but move about in any direction, sometimes MOVEMENT OF IONS 5 reuniting with others, reforming the molecule, which again dissociates, and so on. When, however, an electric cur- rent flows through the solution, the ions move in definite directions. Those with the positive charge (the sodium ions) move in the same direction as the current, and those with the negative charge (the chlorine ions) move in the opposite direction. This orderly movement of the ions is due to the following causes. The conductor along KAT HODE- AWODE ■* 1 of curretill + _ / ^ (gg) (EDd-d-> /So) *-/Va (^ (SS) ^'^"^ ^/^* (F^ CI-* ^^ £i^ Fig. I. — Passage of current through a solution of sodium chloride. Sodium ions migrating to kathode, chlorine ions to anode. Undivided sodium chloride mole- cules move in no definite direction. which the current enters the solution (known as the positive electrode, or anode) is connected to the positive pole of the battery, and therefore the ions with the positive charge are repelled from it. At the same time they are attracted to the conductor by which the current leaves the solution (the negative electrode, or kathode), because this conductor is connected to the negative pole at the battery. The ions with the negative charge make their way in a direction opposite to that taken by those with the positive charge, because they bear the opposite charge. The 6 ESSENTIALS OF MEDICAL ELECTRICITY ions with the positive charge, therefore, travel in the same direction as the current "down-stream," while those with the negative charge make their way in a direction opposite to that of the current "up-stream." Those events are shown diagrammatically in Fig. i. Now when the ions reach the electrodes to which they are attracted, their electrical charges are neutraHsed and further chemical changes occur. These depend on the nature of the ion and on the material of which the electrodes are made. Assuming that the electrodes are made of a metal like platinum, which resists corrosive action, the positively charged sodium ion reaches the kathode and its electrical charge is neutralised, where- upon the sodium, now in the free unelectrified state, resumes the properties of free sodium and decomposes the water, forming sodium hydrate (caustic soda) and free hydrogen. The negatively charged chlorine ion reaches the anode and becomes free chlorine, some of which, in the nascent state, decomposes the water, forming hydro- chloric acid and oxygen (Fig. 2). These are not the only changes that take place at the poles. It will be sufficient, at this stage of our inquiry, to say that bodies of an alkaline reaction form at the negative electrode (kathode). If red Htmus is around this electrode it will turn blue. If the positive electrode (anode) is made of some metal that resists the action of acids, such as platinum, acids will be formed around this pole and can Likewise be demonstrated by litmus. The passage of the electric current through the solu- tion, therefore, produces two main changes. In the first place, the ions between the electrodes of entry and exit of the current migrate in definite directions, those with the + charge migrating towards and accumulating at the negative electrode, those with the - charge migrating towards and accumulating at the positive electrode. There is therefore a redistribution of ions between the IONS AT THE ELECTRODES electrodes along the path of the current. In the second place, new chemical bodies are formed at the electrodes. When a current of electricity passes through any part of the body, similar events take place. The tissue fluids contain many other salts besides sodium chloride — viz. carbonates, chlorides, phosphates and sulphates of \ KAT HODH AfV JK DireclioTi T 1 oh Ci^rrent 1 ODE + •"S,- p) €3) jO- ^ut ^o) (@ <^ OH-* ♦•H CI"* Fig. 2. — Passage of current through solution of sodium chloride. Sodium ions reach kathode and caustic soda and hydrogen (not shown) are formed. Chlorine ions reach anode and hydrochloric acid and oxygen (not shown) are formed. Some of the caustic soda molecules and hydrochloric acid molecules dissociate and + _ + _ form ions Na and OH ; and H and CI. sodium, potassium, calcium, magnesium and iron, be- sides organic soluble salts, so that there are other ions as well as the sodium and chlorine ions. The two last- mentioned are, however, present in the largest number. The sodium hydrate which forms at the negative electrode has a caustic action on the tissue. So also has the hydrochloric acid which forms at the positive electrode. Either may be used for the destruction of tissue. This, the so-called electrolytic action of the current on the 8 ESSENTIALS OF MEDICAL ELECTRICITY tissue, is really the chemical action of the caustic pro- ducts formed at the electrodes. Here we have one of the examples of the mode of action of electricity on the body by the production of chemical changes. The electrical current acts in this way when it is used for the destruc- tion of nsevi, warts, moles, etc., and the practical details of the method will be set forth in a later chapter. This method is sometimes spoken of as " surgical electrolysis " or " surgical ionisation." There is, also, in the tissues, a migration of ions be- tween the electrodes and a resulting redistribution. The conditions are more complicated in the case of the tissues than in the simple salt solution. There are various ions in the tissues and they are not in the same relative pro- portion or concentration in the various organs. Thus the tissues of the nervous system contain more potassium salts and phosphates, while the blood and lymph contain more sodium chloride and carbonate ; that is to say, in + the former there are more K ions and PO4 ions ; in the + _ _ latter, more Na ions and CI and CO3 ions. When the current traverses these tissues there must be some re- arrangement in the relative proportion of the various ions in them. When, in cases of disease, the application of the electric current produces a beneficial effect, the mode of its action may be found perhaps in the migration and redistribution of the ions in the diseased part, some upset in the balance having possibly taken place in the disease or possibly some new ions having been formed. It is, of course, very difficult in the present state of our knowledge to show the exact relation between ionic redistribution and therapeutic action. The following examples are suggestive as to the mode of action of the electric current by producing a redistribution of ions along the path of its flow. The constant current has the power to quickly abolish PASSAGE OF IONS THROUGH SKIN 9 the feeling of fatigue from a heavily worked muscle. This was spoken of as the " refreshing " action of the current. What probably happens is as foUows. Fatigue products (perhaps sarcolactic acid or its salts) accumu- late in the muscle. The passage of the current through the muscle causes migration of these ions and many pass out of the muscle and into the blood vessels and lym- phatics of the muscle and are then at once carried away by the circulating fluid. The refreshing effect produced by passing the constant current through the brain (cerebral galvanisation) is possibly due to a similar action, the removal of fatigue products as a result of their migration accompanying the passage of the current. The power of the current to produce migration of ions can be utilised for a third purpose. If a solution con- taining ions is placed in contact with any part of the body and the current made to traverse the solution on its way through the body, the ions will migrate as previously described, so that some will pass through the skin into the body, and others, bearing the opposite charge, will pass in the opposite direction out of the body. The electric current can therefore be used for the purpose of introducing electrolytes (or, more correctly, their ions) into the body. A large number of drugs used in medicine are electrolytes. The current can therefore be used for the purpose of introducing drugs into the tissues, and the method is known as the " ionic method." We have, therefore, three examples of the way in which electricity produces therapeutic effects by means of the chemical changes which it can induce. These may be briefly re-stated : I. The production of new chemical bodies at the electrodes of entry and exit of the current into and from the body. These bodies have a caustic action, and are used for the destruction of diseased 10 ESSENTIALS OF MEDICAL ELECTRICITY and unnecessary tissue. The process is known as " surgical ionisation." 2. The rearrangement of ions along the path of the current through the tissues. 3. The introduction of new ions from without. The process is called " medical ionisation," and the method is known as the " ionic " method. The changes mentioned under 2 and 3 are on the border-line between chemical and physical ; they may be called physico-chemical. While the current is passing through the body it stimulates the excitable tissues, as indicated by the subjective sensations produced, such as pain, the feeling of burning and pins and needles. These sensations are in all probability the result of the movement of ions through the sensory nerves and end-organs. If the current flows constantly in the same direction and with strength un- varied, no muscular contraction is noticed. The steady movement of the ions stimulates sensory nerves, but not motor nerves or voluntary muscle. If, however, the movement of the ions is suddenly stopped by switching off the current, the muscles give a single twitch at the moment the current is interrupted. A single twitch is also noticed at the moment when the current is switched on again, and the movement of the ions again suddenly started. An abrupt start of ionic movement or cessation of movement is therefore necessary if voluntary muscle is to be stimulated to contract. The former happens to be a more effective stimulus than the latter, so that the twitch occurring at the moment when the current is switched on (the so-called " closure contraction ") is larger than that occurring at the moment when the current is switched oft (the "opening contraction"). Other tissues, besides muscle and nerve, are in all prob- ability stimulated, and the beneficial action of electricity in the treatment of certain conditions (of which paralysis IONIC OSCILLATION ii may be mentioned as one) is not to be attributed to any mysterious or vital action of the electricity, but rather to the stimulation of the tissues produced by the ionic movement that is a necessary accompaniment of the passage of the electric current. Just as a sudden movement in the same direction or sudden cessation of movement of ions will cause a voluntary muscle to contract, so will a sudden reversal of their movement. If the reversal is slow, the current slowly sinking to zero and then rising to its maximum with equal slowness, but in the opposite direction, there will be no contraction of muscle, but a sensation of smarting and pricking will be perceived, because the slow to-and-fro movement of the ions acts as a stimulus to sensory nerves, but not to voluntary muscle or motor nerves. If the reversal of the current becomes more frequent, the ionic oscillation will become sufficiently frequent to stimulate motor nerves and muscle, and contraction will occur. With a still greater frequency of current reversal and ionic oscillation aU sensation will disappear, except that due to the contraction of the muscles. Finally, when the frequency of the current reversal becomes extremely high — a million or more reversals taking place each second (this is the so-called " high-frequency " current) — ^there will be no contraction of muscles and no stimulation of nerves, and there will be no chemical change of any kind. This inability of the high-frequency current to produce the physiological phenomena that are brought about by the constant current or the current that oscillates with a lower frequency had, for many years, received no satis- factory or intelligible explanation. But if the pheno- menon is considered in the light of the behaviour of the ions that accompanies the flow of the current, and the electrical stimulus regarded as a sudden ionic movement, it receives a satisfactory explanation. If the current 12 ESSENTIALS OF MEDICAL ELECTRICITY travels to and fro with a frequency of a million or more per second, the ions are unable to keep pace with it : they remain stationary, and there is no ionic movement. During the millionth part of a second for which the current is flowing in any one direction before it reverses, the ions have been unable to move, or, at any rate, to move sufficiently to bring about a stimulation of excit- able tissue. Now that it is possible to pass an electric current through the body without stimulating the excit- able tissue, and without producing chemical change, we are able to utilise electricity for the production of heat within the body. Since the high-frequency current does not stimulate the excitable tissues, it may be sent through the body in strength far greater than that per- missible for constant or low-frequency current, and it will then develop heat on its path through the tissues as it overcomes their resistance. The constant current or low-frequency current are unable to act in a similar way, because they would produce violent muscular contrac- tion and unbearable pain long before they reached a strength sufficient to develop heat. The heat that is generated by the high-frequency current is developed on the path along which it flows, so that the deep-lying tissues are heated as well as the superficial. The raising of the temperature of the deep as well as the superficial tissues is known as " diathermy." It forms an impor- tant branch of medical electricity, and is described in Chapter XII. High-frequency currents were used in medicine for many years without a clear knowledge of the way in which they produced their physiological and therapeutic effects. The recognition that these results were due to the development of heat within the tissues and organs showed that the high-frequency apparatus then in use for medical purposes was not suitable for the production of much heat. The modern diathermy apparatus has ACTION OF STATIC BREEZE 13 since been evolved with this end in view — viz. the generation of the largest quantity of heat. The development of heat within the tissues by the high-frequency current is an example of the other mode of action of electricity on the body — viz. by the pro- duction of physical effects. The physical effect is, in this case, the development of heat. In the case of the constant current and the currents of low-frequency oscillation, the effects are chemical or physico- chemical, and are brought about through the agency of ionic movement ; in the case of the high-frequency current the effects are thermal and the ions are not moved. Electricity can produce chemical and thermal effects in another way, quite different from that already described. The static breeze and high-frequency effluve will illus- trate this. These forms of electrical application will be described later, but here it may be said that electricity at a very high potential is applied, so that if an air-gap is inserted between the electrode and the patient's body, the electricity, if directed from a pointed electrode, is able to bridge the gap in the form of a brush of nearly silent violet sparks, scarcely visible except in the dark. The application of this brush to the skin strongly stimulates the latter. The stimulation is due most probably to the heating of minute points of skin. Erythema is produced and even urticaria, if the applica- tion is strong. We are able, in one instance at any rate, to trace the physical, physiological and therapeutic re- sults of the appHcation of electricity. A patient suffers from headache as the result of low blood pressure. The application of the static breeze induces an er3^hema by the heating of minute points of the skin, and, as a physiological result of peripheral stimulation of the sensory nerves, there is a reflex rise of blood pressure and the headache disappears. 14 ESSENTIALS OF MEDICAL ELECTRICITY The passage of the brush discharge through the atmospheric gases causes the formation of ozone and nitrous and nitric acid. It is probable that these chemical products play a part, by virtue of their germicidal action, particularly in the treatment of some skin affections and infected ulcers. The application of sparks from a static machine wUl frequently reheve pain in the region of muscles and fasciae — e.g. the Imnbar region — and the relief is some- times instantaneous. The mode of action of electricity in such cases is, most probably, mechanical. The sudden powerful muscular wrench that accompanies the passage of a long spark breaks down adhesions. The static wave current also produces rhythmic muscular twitches, but less violent and more agreeable than those produced by the sparks. In bringing about relief, as it often does, in certain cases of chronic inflammation and congestion {e.g. traumatic synovitis, chronic neuritis, etc.), electricity, in the form of the static wave current, produces its results by physical (mechanical) methods. In applying the static wave current (the details wiU be given later) the body is alternately charged and discharged, the electricity suddenly escaping, during discharge, by way of an electrode placed in contact with the part requiring treatment. The therapeutic results are to be attributed, not directly to the electricity, but rather to its power of producing physical (mechanical) changes, the rh5rthmic twitching of the muscles inducing local acceleration of the circulation and mechanical removal of the effusion and loosening of adhesions. It is not pretended that the account given in this chapter of the mode of action of electricity will explain, in every case, the way in which disease responds to electrical treatment. But if we look upon the cure or relief of disease by electrical methods as due, not directly ACTION OF STATIC BREEZE 15 to the electricity itself, but rather to known chemical or physical changes that it produces, we are better able to judge whether electrical treatment is suitable for a case, and foresee the results that may be expected from its application. CHAPTER II THE CONSTANT CURRENT AND ITS MODIFICATIONS The various methods of applying electricity for the treatment of disease are, to all outward appearance, very dissimilar, as will be apparent to one who visits a modern electrical clinic. Yet in the greater number of cases an electrical current is applied, modified, in one way or another, and producing different physical and physio- logical effects. Each current may be derived, directly or iadirectly, from one source — ^that is, the constant current. In this chapter it is proposed to describe the various modifications of the electrical current, taking the constant current as the starting-point. The Constant Current. — ^This current is so called because its strength does not vary and its direction of flow does not change. It is sometimes called the " continuous current," sometimes the " galvanic current." The constant current supplied on the mains in certain districts is generally called the " direct current," or, for short, DC. The constant current may be obtained by chemical action, such, for example, as that which takes place in a battery cell or accumulator, or by mechanical action, as in the revolution of the armature of a dynamo. This current can be accurately measured. When it is to be used for medical purposes we should know its voltage and its amperage. These are measured by the voltmeter and amperemeter respectively. The amperage expresses the strength of the current, or, more accurately, the quantity of electricity passing along the i6 SIMPLE INTERRUPTED CURRENT 17 circuit ; and the voltage is a measure of the pressure or force at which the electricity is impelled onwards. A graphic representation of the constant current would be a horizontal straight Line parallel to a base-line repre- senting zero, and above it or below it according to the direction of the current, while the distance above it or below it would indicate either its pressure or its strength. For medical purposes this is probably the most impor- tant and generally useful form of electrical current we have. Simple Interrupted Current. — ^This current flows always in the same direction, but the flow is intermittent, H Fig. 3. — Graphic representation of simple inter- rupted current. The periods of current-flow and periods of no-flow are, here, of the same duration, not continuous. There are alternate periods of flow and no-flow. During each period of flow the current strength is constant. At the end of this period the flow ceases suddenly, and the period of no-flow follows. At the end of the latter period the flow is suddenly resumed. A graphic record of a simple intermittent current is shown in Fig. 3. BC represents a period of flow, DE a succeeding period of no-flow. CD represents the sudden cessation of the current, EF its sudden resumption. The height of the hne above the base-line would be proportioned to voltage or amperage ; the distance along the base-line would indicate time intervals. Such interruptions of the current can be produced by alternately making and breaking the circuit along which the current flows. This can be effected by various mechanical devices. A simple make -and -break key can i8 ESSENTIALS OF MEDICAL ELECTRICITY be introduced into the circuit and operated by hand. A metronome can be adapted (Fig. 4), so as to produce regular and even interruptions. The swinging arm bears a horizontal wire, to each end of which is fixed a short vertical wire. Another vertical wire of equal length is fixed to the centre of the horizontal piece. When the arm of the metronome swings to and fro, the horizontal wire moves with it, and the vertical wires at the extremity of the latter rise and fall. Three small cups of mercury are fitted to the metronome, and so arranged that as the vertical wires fall and rise they dip into and rise out of the mercury in the cups. The central vertical wire does not rise or fall, but stays permanently immersed. The vertical wires that dip into the mercury should be made of silver. A terminal is connected to each cup. To use the metronome as a current interrupter, one end of the wire conveying the current is attached to the central cup, the other end to one of the end cups. When the wire rises out of the mercury the current is inter- rupted. The number of interruptions per minute will depend upon the rate of swing of the metronome. The time the current flows between each interruption depends upon the rate of swing of the metronome and the depth to which the wire dips into the mercury. The metronome can be used to interrupt two currents alternately. Of the wires conducting the second current one is connected Fig. 4. — Metronome Interrupter MECHANICAL CURRENT INTERRUPTER 19 to the other end cup, the other wire to the central cup. The metronome interrupter may be used when regular interruptions of a current are desired without accurate measure of their duration. It is used in the process of muscle-testing by the condenser method, and in some forms of electrical , treatment. ^ ' Another device for procuring simple interruption of the constant current is Leduc's mechanical interrupter. By means of this instru- ment the current may be interrupted as frequently as de- i ^* — c sired, and the periods Fig. 5.— Plan of commulator of Leduc. of flow and of in- When the current flows Irom the fixed brush-holder AB to the movable brush- terruption may be holder in the position CD, the period of varied and accurately current-flow is the longest and of no-flow 1 the shortest. measured. When the movable brush-holder is in Leduc's Mechanical the position C'D', the period of current- Current Interrupter, fj^^^^' ^^^ '^""'^^'^ ^"^ ""^ "^-^^"^ ^^^ — ^The essential part of the apparatus is a disc of insulating material mounted on the axle of a small motor and rotating with it (Fig- 5). Four metal strips are secured on the circumference, each being of equal length. They are placed symmetrically around the circumference. There is a small interval between consecutive strips. Dia- metrically opposite strips are in metallic connection with each other. Two contact brushes press against the circumference of the wheel, one being fixed, the other being movable through an arc of 90°, so that it may 20 ESSENTIALS OF MEDICAL ELECTRICITY touch the circumference at a point diametrically opposite the fixed brush, or at any point nearer, but not closer than one quarter of the circumference. The current can pass from one brush to the other, so long as the brushes are in contact with diametrically opposite pairs of discs. When the brushes are in the position shown in Fig. 5 (continuous lines), the current can flow from one strip to that opposite and continue to flow, when the strips are revolving, for the longest time possible. But when Fi(}. 6. — Leduc's Mechanical Interrupter the movable brush has been moved round through 90° the current can flow only for the shortest time. In the first position the current flows for the longest time and the period of no-flow is the shortest. In the second position the period of flow is the shortest and that of no- flow is the longest. Intermediate positions of the brush give other periods of flow and no-flow. Increase of the length of the time of current-flow shortens the period of no-flow, and vice versa. The number of interruptions of the current depends upon the speed of revolution of the disc. The number of revolutions per second can SIMPLE ALTERNATING CURRENT 21 be indicated by a speed indicator. Increase of the speed of the interrupter will shorten the periods both of flow and no-flow. By means of this current interrupter it is possible to vary the number of interruptions and measure the duration of the period of flow of the current, and the period of no-flow. The interrupter is shown in Fig. 6. Simple Alternating Current. — ^This current differs from the simple interrupted current in that it flows, dur- ing successive periods, in opposite directions. A graphic B yi ■ f c C D A D' £ F B B T Fig. 7.— Ruhmkorffs Commutator record of such a current is shown in Fig. 8. Between the successive periods of current -flow there are periods of rest, so that the current is intermittent as well as alternating. The simple alternating current may be obtained from the constant current by means of the device known as a Ruhmkorff's commutator. This is often fitted to galvanic batteries and induction coils for the purpose of reversing the direction of the current when desired. If it is attached to the revolving axle of a motor, the direction is periodically reversed at a rate depending on the speed of revolution of the motor, so that a simple alternating current is provided. The Ruhmkorff commutator (Fig. 7) consists of a 22 ESSENTIALS OF MEDICAL ELECTRICITY cylinder of hard rubber, A , mounted on a spindle, B so as to revolve freely. On each end of the cylinder are fixed metal bands, C and D, and from one side of each band the metal extends for about two-thirds the length of the cylinder, in the form of cheeks C and D' , but not so far as to come into contact with the band at the opposite end. The cheeks C and D' are usually made to embrace about one-fourth the circumference of the cylinder and are so fixed as to be exactly opposite each other. Four metal springs are now required. A pair, EE, is mounted one at each end of the cylinder, so as to press on the metal Fig. 8. — Graphic representation of a simple interrupted and alternating current. The periods of current-flow are here equal to the periods of no-flow. bands, C and D. The other two, FF, are mounted on opposite sides of the cylinder at its middle, so as to touch the cheeks, C and D' , as the cylinder is revolved. The wires from the battery or other source of constant current are connected to the springs, EE, and the current led off by wires joined to the springs, FF. It will be seen that the direction of flow tDf a current in a wire joining the springs FF will be reversed each time the cylinder is rotated through half a revolution, and if the rotation is kept up the wire wiU be traversed by a simple alternating current. Such a current is graphically represented in Fig. 8. When the space between the metal cheeks is equal to the width of the cheeks, each period of flow of the current is followed by a period of rest of equal SINUSOIDAL CURRENT 23 duration. This period of rest can be increased or diminished by varying the width of the metal cheeks. A commutator for practical use is made so as to give from four to eight or more cycles per revolution, and so obviate the necessity for driving it at very high speed. The principle of its construction is the same as the one here described. Sinusoidal Current.— This current is supplied on the main in certain districts under the name " alternating Fig. 9. — Graphic representation of a sinusoidal current — one complete phase. current." It is a very useful current for many medical purposes. It can be taken direct from the main where the supply is an alternating current ; where the supply is a constant (direct) current, the latter can be readily converted into a sinusoidal current by a motor trans- former. To understand the way in which a sinusoidal alternating current is generated requires some know- ledge of the mechanism of dynamos. This is briefly described on page 289. The sinusoidal current is an alternating current, but it differs from the simple alter- nating current just described, in that its rise from zero to 24 ESSENTIALS OF MEDICAL ELECTRICITY maximum and its fall from maximum to zero is gradual, not sudden. Further, on reaching zero, there is no period of intermission, but a second rise to maximum and fall to zero in the opposite direction. A graphic representation of a sinusoidal current is shown in Fig. 9. From A to B the current is rising to its maximum ; from B to C it is falling to zero ; from C to D it is rising to a maximum again, but the current is flowing in an opposite direction ; from D to E it is falling again to zero. ABCDE represents a complete cycle or phase. The Fig. 10 " periodicity " of the current refers to the number of these complete cycles per second. If the current has a periodicity of 100, there are 100 of these cycles each second. From A to E the time interval would be yJo^h second ; from A to C g-J^th second. The height of the curve above the base-line at any spot is proportioned to the voltage or amperage. The alternating current supplied on the main is gener- ated at the power station by a d3mamo. When the direct current is supplied on the mains, or when it can be obtained from a battery of accumulators, a sinusoidal current may be readily obtained by means of a motor transformer. Makers of electro-medical apparatus now SLOW SINUSOIDAL CURRENT 25 put on the market different patterns of so-caUed "universal" apparatus, sold under the trade names of " Pantostat," "Multostat," '' Polystat," etc., and these convert constant into alternating sinusoidal currents. Such instruments are now largely used, and one pattern is illustrated in Fig. 10. Slow Sinusoidal Currents. — ^The alternating cur- rents on the mains have a periodicity not higher than 100 and not lower than 25. If there are fewer than 25 complete cycles per second {i.e. 50 reversals per second), lamps that are illuminated by such a current will not give a steady light. Sinusoidal currents of a lower periodicity are sometimes used in medicine, and Dr Reginald Morton has recommended the use of currents with a periodicity as low as 1-7 — that is, in each second there are 1*7 cycles. The duration of each cycle would then be very nearly 0-6 seconds. A slow sinusoidal current may be obtained from a motor transformer that is made to revolve slowly. This method is, however, very wasteful of current. A better method is to use a rhythmic reverser, such as that of Ewing. This is shown in plan in Fig. 11. The following description is taken from Dr Lewis Jones : — " An insulating drum of ebonite is revolved in a glass cylindrical vessel of water which it nearly fills. There are metallic armatures, CD, inside the vessel at opposite ends of a diameter. Corresponding armatures, A and B, are fixed to the ebonite drum. If a difference of potential be maintained between C and D, as indicated by the signs + and - , there will be a flow of current from A to B through a conducting circuit joining these points, when the drum is in the position shown in the figure, and if the drum is turned round through 180° there will be a flow from jB to ^ as the positions of A and B relative to the armatures C and D will have been reversed. Thus by 26 ESSENTIALS OF MEDICAL ELECTRICITY rotating the ebonite drum a sinusoidal current will be set up in the circuit A B. It will reach its maximum when the armatures A and B are close to C and D and will be at zero when they occupy the positions at right angles to this. To utilise the current in the circuit A B it must be collected by means of rings and brushes very Fig. II. — Plan of Ewing's Rhythmic Reverser much in the way used with an alternating current dynamo." Faradic Current. — This is the current that is obtained from the induction coil. The induction coil does not actually generate the current, but transforms the current of the battery attached to it. The latter is a constant current of low voltage. The coil transforms it into one of much higher voltage with corresponding diminution of amperage, and at the same time makes it intermittent and alternating. A graphic record of such a current is INDUCTION COIL 27 shown in Fig. 13. It may seem unnecessary to the student to consider the matter of the output of induction coils, but the subject is important, as a clear understand- ing of it will show why it is that some medical coils produce painful and disagreeable results when used for treatment, and will show why the induction coil is not the most suitable instrument to employ when accurate results are desired in the investigation of the reactions of muscle and the physiological response of excitable tissues. '" Before describing the meaning of the curve shown in Fig. 13 an account of the induction coil will first be given. The induction coil is probably the best known electrical device in use by medical men and others. It is very inexpensive, especially in its simplest forms, and for stimulating living tissues it may be quite efficient. From the fact that it lends itself very readily to great variation in constructional detail, without seriously interfering with its working qualities, few instruments have been subjected to such extensive modifications — and though much ingenuity has been expended on it, it is doubtful if any substantial improvement has resulted. Notwithstanding its complicated appearance, especi- ally to the uninitiated, the induction coil is really a very simple appliance. Its essential parts^are Jshown in Fig. 12. A is an iron core — ^usually made up of a bundle of soft iron wires — ^around which is wound a comparatively few turns of fairly coarse wire : this is the primary coil. In all cases the wire used for winding coils is covered with silk or cotton for purposes of insulation. Opposite one end of the core is an iron block, B, which is secured to the end of a metal spring, C. A screw, D, is mounted so that its point comes opposite about the middle of the metal spring. The end of the screw and that part of the spring 28 ESSENTIALS OF MEDICAL ELECTRICITY with which it comes into contact are both faced with platinum. One end of the primary coil is connected with one pole of the battery, E — ^the other is connected to the spring, C. The other pole of the battery is connected to the screw, D. Around the primary coil, but quite disconnected from it, is another coil of much finer wire and Wound in very many more turns. This is the secondary coil. It is not shown in Fig. 12. The secondary coil generally consists of a large number of turns of fine wire. It is not directly connected in any Fig. 12 way with the primary, but is wound on a bobbin, the hole through the centre of which is large enough to slide over the completed primary coil. By so doing the secondary is brought more or less into the magnetic field of the primary, and the electro-motive forces in it thereby adjusted. The secondary has from five to fifteen times the number of turns of the primary, for which it is made. The average proportion of primary turns to secondary turns is i : 10. The course of the current can be easily traced from the battery to the primary coil, from this to the spring, C, thence through the platinum contacts to the screw, D, and so back to the battery. The current passing round the primary coil, the latter becomes, with the iron core, FARADIC CURRENT 29 an electro-magnet. It thus attracts the iron block, B, and in drawing the latter towards itself pulls the spring, C, away from the point of the screw, D. Immediately this happens the circuit is broken and the flow of current from the battery ceases. The core thus loses its magnet- ism, and the iron block no longer attracted, the spring, C, by its own elasticity flies back until it is stopped by the point of the screw, D. The circuit is thus again closed and the above-mentioned changes are repeated. We may now consider the events that take place in the primary and secondary coils. Since the vibrating spring continually makes and breaks the primary circuit, the current flowing in this circuit (the primary current) is interrupted or intermittent. Further, at " make " and also at "break," an extra current is induced, not only in the primary circuit (the primary induced current), but also in the secondary circuit (the secondary induced current). These induced currents are of momentary duration. They may be taken in order : 1. At " Mcle" of the Pir.mary Circuit. — ^The battery current flows around this circuit, but at the same time a new current of momentary duration is induced in the same circuit ,and it flows (as mentioned in Chapter XV., p. 287, under Self-induction) in the opposite direction, impeding it and slowing its rate of rise to its maximum. This is shown in Fig. 13, a to h. It indicates the slow rise of the current in the primary to maximum. As a result of this impeded rise, the current that it induces in the secondary coil is of correspondingly long duration and does not reach so high a voltage (see Fig. 13, curve from . A to B). 2. At" Break " of the Primary Circuit. — ^At the moment the primary circuit is interrupted the battery current ceases to flow, and at the same time an extra current is induced in the same circuit ; it flows in the same direction as the battery cturent, and therefore the induced current 30 ESSENTIALS OF MEDICAL ELECTRICITY is not impeded, but increased, and the cessation of the current in the primary circuit is abrupt (Fig. 13, h to c). The abrupt cessation of the current in the primary in- duces in the secondary a current of brief duration, briefer than that of the current induced in the same coil at " make " and one at higher voltage (Fig. 13, BCD). It is evident, then, that the faradic current is highly complex. Further than this, the graphic record of the A BCD -Induced current in. secondary/ coll AB- Make Curreat BCD- Break Current (tcusfinj 0-0037 ict.) odbc - Exciting current in primary coil ab- Make Current be -Break Curreut Fig. 13. — Graphic record of the primary and secondary currents of an induction coil. [Adapted, by permission, from Jones' Medical Electricity. 6th Edition. H. K. Lewis & Co. Ltd., London. output of induction coils varies greatly in coils of differ- ent design. The output depends on the length of wire in the primary and secondary coils, the presence or absence of an iron core, the design of the vibrating spring, the method of regulating the output, etc. The output may^ also vary in the same coil from time to time, according to the adjustment of the hammer, etc. We may therefore speak, not of a faradic current, but of varieties of faradic current. Any type of medical coil will give a current that will stimulate the tissues, but few will give a current RECORD OF FARADIC CURRENT 31 that will stimulate them painlessly. The question of the output of induction coils is a subject of much importance, both from the point of view of electrical treatment, and also the testing of the reactions of muscle and nerve. The first of these may be considered here ; the second will receive attention in the chapter on the testing of electrical reactions. Motor nerves and muscles will respond to currents of very brief duration. Sensory nerves, however, require currents of longer duration. The current that is pro- vided by an induction coil should last, during each period ABCD - Induced correntm secondary coil AB - Make Current BCD -Break Ci;rrent Fig. 14. — Graphic record of the secondary current from a well-designed coil. [Adapted, by permission, from Jones' Medical Electricity. 6th Edition. H. K. Lewis & Co. Ltd., London. of flow, the briefest possible time, so that muscles and motor nerves may be stimulated, and not the sensory nerves. A coil giving a record like that shown in Fig. 13 would produce painful contractions of muscle, because the secondary current flows for periods that are long enough to stimulate sensory nerves. Many other coils give currents that produce the same effect. A coil that is most suitable for medical treatment is one that produces the most vigorous contractions without disagreeable sensation. This requirement will be fulfilled if the in- duced current in the secondary at " break " is of the 32 ESSENTIALS OF MEDICAL ELECTRICITY shortest possible duration, and that at " make " being of insufficient strength to cause skin sensation or muscular contraction. A coil giving a graphic record like that shown in Fig.. 14 would give the most agreeable and painless contraction of the muscles. The records in Figs. 13 and 14 are on the same scale. The record of the secondary- current is given in Fig. 14 (not of the primary), and it will be seen that the duration of the current at " break " BCD is very brief (yoVxr second) ; that at " make " being of Fig. 15 insufficient intensity to cause perceptible stimulation. An electrical stimulus or impulse is produced each time the current at " break " flows. The number of these im- pulses per second depends on the rate of vibration of the spring. In the record shown the number was nearly 100 per second. Such a coil (Fig. 15) was designed by Lewis Jones, and the oscillographic record shown in Fig. 14 was obtained from one of this design. It is a valuable coil for use in medical practice, as the current wiU evoke strong muscular contractions without disagreeable sensation. It is enclosed in a case containing a dry cell and is portable. The primary circuit is completed and interrupted by a spring vibrating in a horizontal plane and actuated by the iron core within the primary coil. This core is not REQUIREMENT OF INDUCTION COILS 33 movable. The secondary coil can be made to slide as a sledge over the primary coil. The current that is applied to the patient is taken from the secondary coil and is regulated by sliding the secondary over the primary. Three binding screws are connected to the secondary winding. From two of these the current from only one- third of the length of the secondary wire is taken. This Fig. 16. — Sledge Coil current is of lower voltage and is the most suitable when it is to be applied to the body through the damp skin by way of moistened pads, so as to lower the resistance. From another pair of binding screws the current from the whole length of the secondary is taken. The current is of higher voltage and is the one to be chosen when it is to be led through the higher resistance of dry skin. There are many other designs of medical coils on the market. The requirement of a coil that is to be used for medical purposes is the power to produce strong con- traction without pain. The readiest test is the sensation produced on one's own cheek, applying the current 34 ESSENTIALS OF MEDICAL ELECTRICITY through damp pads. The most accurate test is furnished by the graphic record given by the oscillograph. Induction coils fitted with separate electro-magnets for working the vibrating spring produce irregular and uneven impulses and disagreeable sensory stimulation. Many types of coil are made. Some of them are pro- vided with an extra pair of terminals, so that either the primary or the secondary induced current can be applied to the patient. In Fig. 12, ^represents the handles that lead the primary induced current to the patient. The primary current is regulated by sliding a brass tube over the iron core. Other coils have an arrangement in the form of a bent wire and a sliding ball (Fig. 16) fixed to the hammer, for the purpose of regulating tha rate of vibration of the latter. The question of the output of induction coils has been considered at length, because this form of electrical in- strument is so widely used for so many medical purposes, and is not always of correct design. The best test of a coil for medical and physiological purposes is furnished by an oscillographic record. The high-frequency and diathermy currents and the static wave and static induced currents wiU be described later, in the chapters dealing with these forms of electrical appHcation. CHAPTER III SOURCES OF ELECTRICAL SUPPLY When it has been decided to make use of electricity for the treatment of disease, the first practical question which arises is that of supply. There are different sources of supply and the selection will depend on what is available and most convenient. In almost all the applications of electricity for medical purposes, a current of one or another kind is used, and the current which constitutes the source of supply may require modifica- tion according as it is used either for direct application to the body or for the generation of other kinds of currents, or for other purposes. There are the following sources of supply : 1. The Street Mains. 2. Cells and Accumulators. 3. Dynamo and Driving Plant (private installation). Each of these has its advantages and limitations. These will be set forth in the present chapter, together with the methods of modifying them so as to render them suitable for different purposes. For the generation of static electricity an influence machine is required, with an electric motor or gas or oil engine to drive it. Current from the Main — ^The town supply that is distributed along the street mains and taken into many of the houses is the most convenient and economical source. The current is in some towns and districts a direct current (DC.) — i.e. its direction is unvarying. In others it is an alternating current (AC.) — that is, its direction is periodically reversing. The voltage at 35 36 ESSENTIALS OF MEDICAL ELECTRICITY which it is supplied is not always the same in different towns ; in some it may be lOO, in others 200 or 250. And in the case of the alternating current the frequency of the alternation differs in different towns. It is there- fore necessary to find out with regard to the town current whether it is a direct or an alternating current, the voltage at which it is suppUed, and the frequency of Correut Jvom tnaia Cffpcnt jicvn nicnn Fotient B Fig. 17. — Current derived from main with resistance in shunt (A), in series (B). the alternation when the town supply is an alternating current. These particulars are published each year in the January number of The Electrician, The Use of the Direct Current from the Main. — The direct current is the most generally useful for medical work. The voltage at which it is suppUed is in some dis- tricts 100 ; in others it may be as high as 250. The current that is taken to the lamp-holders and plugs has a strength SHUNT RESISTANCE 37 up to 5 amperes. Such a current has too high a voltage and amperage for direct appHcation to the body, and it must therefore be reduced. The simplest and least expensive method of reducing its voltage and amperage is to insert a sufficiently high resistance. This resistance could be inserted in series with the patient, in which case the patient and the resistance would both be in the same circuit, and the current would traverse each in turn (Fig. 17, B). Such an arrangement is unsatis- factory, and the usual plan is to arrange the resistance Plan of Shunt Resistance in shunt. In this case the patient and the resistance are in separate circuits, and the current traverses each simultaneously (Fig. 17, A), the amount passing through each depending on their relative resistances. The re- sistance in the patient's circuit can be varied by includ- ing in the same circuit a varying length of the shunt resistance. This can be effected by connecting one of the wires leading to the patient — ^not to the end of the shunt resistance, but to a point a varying distance along it. With such an arrangement, part of the shunt resistance is in series witfi the patient. Fig. 18 is a diagram showing the necessary arrange- 38 ESSENTIALS OF MEDICAL ELECTRICITY ment. The fine wire coil, from A to B, and the lamp at B constitute the shunt resistance. If we trace out the connections we see that the current comes in from the main at the positive terminal to the switch. When the switch is turned on the current flows through the fine resistance wire from A to B, then through a lamp and safety fuse to the negative terminal of the main. It also flows, when the patient is connected, along part of the length of the fine wire to the slider, C (this can be moved to the right or to the left), then through the galvanometer and through the patient back to the other circuit at B. The strength of current that passes along these two circuits will depend upon their relative resistances. The resistance of the circuit containing the fine wire and the lamp is constant, that of the other circuit containing the patient will depend upon the length of resistance wire between A and the slider, C. On the + side of the connection with the main (Fig. i8) the voltage is at the maximum supplied on the main ; on the - side of the connection it has fallen to zero. The fall takes place gradually and evenly along the resistance from A to B. A further fall takes place in the lamp at B, and zero is reached on the - side of the fuse. From A to B the fall is even — there is a " slope of potential," as it is called. If we take a sensitive volt-meter and connect one terminal to B, and having attached a piece of wire to the other terminal of the volt-meter, draw the free end of this wire across the turns of the resistance from B to A, we will find that we can get any voltage we desire from zero up to the highest given by the instrument — this will be from 50 to 80, depending on the resistance of the lamp at B. Now it will be seen on reference to Fig. 18 that the patient is connected in the same way as the volt-meter. One of the terminals that lead to the patient is connected SHUNT RESISTANCE 39 to B, the other is connected with the sUder, C, which can be moved along the resistance coil, AB, and in con- tact with it. This slider, C, is mounted on a metal rod that is placed parallel to the resistance coil and at such a distance from it that its springs are always in contact with it. The voltage of the current that passes to the patient can therefore be varied between zero and maximum by sliding, C, along the resistance coil from B to A. When the slider is at B, the terminals that lead to the patient will be in connection with the same region of the resistance coil, and there will be no d ifference of potential between the termi- nals, and no current will pass to the patient. On moving the slider farther and farther away from B towards A, the vol- FiG. 19. — Shunt Resistance tage between the terminals will rise higher and higher, and more and more current will pass to the patient. Its value is indicated by the milliampere-meter placed in the same circuit with the patient. Fig. 19 is an illustration of the actual apparatus the plan of which has been described. The various parts are mounted on a board that can be fixed permanently 40 ESSENTIALS OF MEDICAL ELECTRICITY to the wall. At the top are mounted the lamp, switch and safety fuse. Underneath is the resistance coil. In front of this is the slider which can be moved from side to side over its surface. The scale below the resistance coil serves to indicate the position to which the sUder has been moved on any occasion. At the bottom of the Fig. 20 board are two terminals to which will be fixed the cables that lead the current to the patient . A milHampere-meter IS not attached to this board. Fig. 20 shows a similar apparatus, contained in a box, so that it is portable. The current which is given by the apparatus described may be varied, by adjusting the position of the slider, between a fraction of a milhampere and 300 milliam- peres, so that it is suitable for all purposes for which a constant current has to be applied direct to the body — SHUNT RESISTANCE 41 viz. ionisation, electrolysis, etc. Its voltage can be varied between zero and a maximum of about 80. Fig. 21. — Galvano-faradic Outfit The current that is taken by the apparatus from the main is not large, and it may be taken with safety from a lamp-holder or wall plug. 42 ESSENTIALS OF MEDICAL ELECTRICITY A more elaborate switch-board is shown in Fig. 21. A volt-meter and a milliampere-meter are fitted so that the voltage and amperage of the direct current that is sup- phed to the patient can be measured. There is also a reverser, so that the direction of the current may be altered as desired. An induction coil is also fitted. It is worked by the current from the main, suitably reduced by the lamp shown on the top left-hand corner of the board. Either the faradic or the direct current can be led to the two binding screws shown at the bottom of the board, and thence to the patient, according to the adjust- ment of the de Watteville key shown on the left side of the board just above the induction coil. The volt-meter is not essential, but it is very con- venient to have. It shows the difference of potential between the electrodes applied to the patient, and by its use rough approximations of the resistance between the electrodes can be arrived at by taking the reading in volts and milliamperes and working it out by Ohm's law. The direct current from the main may also be used for heating the cautery, but here again it requires modifica- tion. A cautery has a very low resistance, a small fraction of an ohm, which is very much lower than that of the body. Therefore a much lower voltage is required. Two volts will usually be sufficient, while that of the main current (100 to 250) is far too high. On the other hand, the cautery requires a high amperage (say 12 to 18), which is higher than that of the current supplied to houses for lighting purposes and very much higher than that of the current given by the apparatus described above (viz. a maximum of 300 milliamperes, or 0*3 ampere). Neither this apparatus nor the unaltered main current are suitable* for cautery. It is possible, however, to obtain a cautery current from the main by using an apparatus of the same type as that described, but modified in the following way. The shunt resistance SHUNT RESISTANCE FOR CAUTERY 43 should be much lower, and should consist of fewer turns and of stouter wire. A lamp is not included in the circuit, as it would add too much resistance. A slider is fitted so as to move along the shunt resistance and so regulate the amount of current that is taken to the cautery. For finer regulation a rheostat (a vari- able resistance) is inserted between the slider and one of the terminals leading the current to the cautery. A plan of the device is shown in Fig. 21. It has the disadvantage of being very wasteful of current. For Adjustable RheoiUt Fig. 22. — Shunt Resistance for Cautery this reason a small lamp is inserted, as shown in the figure, to act as a signal that the current is flowing so that it may be turned off when it is no longer required. This lamp, it will be seen, is inserted in shunt with the resist- ance not in series with it, so that it will only take a very small proportion of the current. Another disadvantage is that it cannot be connected to a lamp-holder or wall plug. It takes a very large current (because the shunt resistance is low and no amp is included in series with it), and if it were connected to a lamp-holder or wall plug the safety fuse would melt and the current would be cut off. If the practitioner has 44 ESSENTIALS OF MEDICAL ELECTRICITY not heavy cables taken into his house from the street mains specially adapted for heavy currents, he will have to derive the cautery current from accumulators or from a machine known as a " motor generator " or " motor transformer." This is a combination of an electric motor and a dynamo or generator. The current from the main causes the revolution of the motor, which in its turn actuates the dynamo. The djmamo generates the new current and it can be wound so that this current has the voltage and amperage desired. The motor generator is illustrated and further described on p. 45. For the illumination of surgical lamps like those fitted to the ophthalmoscope, cystoscope, etc., we require a current of lower amperage than for cautery, but higher voltage. If the lamp filament is long and thin it will have a higher resistance, and the current must be at higher voltage. Short, thick filaments have a lower resistance and require a lower voltage, but a higher amperage if it is to be raised to incandescence. For quite small lamps the apparatus first described, for providing currents suitable for direct application to the body, may be used. For larger lamps, accumulators or a motor generator should be used. Or a suitable shunt resistance constructed on the same plan as that for cautery may be used. It must be seen that the current which it takes is not heavier than that for which the house cables are intended to carry. The direct current from the main is also suitable" for working the large induction coils used for the production of high-frequency currents and X-rays. These coils usually take more current than that carried by the cables passing to a lamp-holder, so that it is generally necessary to fit heavier cables. For the diathermy machine the direct current is un- suitable. It must be converted into an alternating current. This is done by a motor transformer, and one UNIVERSAL APPARATUS 45 must be used that can provide an alternating current of at least 10 amperes at 100 volts. The current that is taken by this transformer is heavy and cannot be carried on the house cables. Specially heavy cables must be taken into the house from the street main, sufficient to carry 20 amperes. The use of a shunt resistance for lowering the pressure of the main current is not unattended by risk. The risk lies in the possibility of accidental short-circuiting to earth and so obtaining a much larger proportion of the main current than is desired, or even the whole of it, with disagreeable or disastrous results. How this risk is possible will be explained on page 52, together with the precautions necessary for avoiding it. By using a motor generator this risk may be avoided. Manu- facturers of electro-medical apparatus now make forms of so-called " universal " apparatus. Such apparatus contains a motor generator, and by its use it is possible to derive from the main constant and sinusoidal currents, and currents suitable for cautery and electric lamps. Different forms of " universal " apparatus are sold under the names of " Pantostat," " Polystat," " Multo- stat," according to the maker. A Pantostat is shown in Fig. 10. Mounted on the left side of the base is the motor generator. It is connected to a wall plug or lamp- holder. The constant current from the main causes the revolution of the motor, and two new currents, quite distinct and separate from the main current, are formed. (The principle of the motor generator is described on page 292.) Of these two new currents one is a constant current, suitable for direct application to the body, either through electrodes or by means of the bath. Since this current is on a circuit quite separate from the main circuit, risks of shocks are avoided, as short circuit- ing is impossible. The other current is an alternating current. This can be varied in strength and appUed to 46 ESSENTIALS OF MEDICAL ELECTRICITY the body in the same way as the constant current. Or it can be taken to static transformers (contained in the base of the machine) and transformed into currents suitable for cautery and lamps. As with the constant current, there is the same freedom from the possibility of shocks through short-circuiting. On the base of the machine are two switches and a milliampere-meter. One of the switches reverses the direction of the constant current. The other is for the purpose of leading either the constant current or the sinusoidal, or both together, to the patient or for cutting oil all current. The continuous and sinusoidal currents are taken to the right-hand pair of terminals. The left- hand pair lead off the cautery current. The two middle pairs lead off the current for illuminating lamps, one pair for small lamps, the other for larger lamps. Five shding rods can be pulled out from the base of the machine : one regulates the strength of the current passing to the motor ; the others regulate the strength of the currents for cautery and light, and the sinusoidal and constant currents. The Use of the Alternating Current from the Main. — The voltage at which this current is supplied on the mains differs in various towns and districts. In some it is lOO ; in others it is as high as 250. The amperage of the current taken into the houses for lighting purposes is the same as for the direct current. The periodicity is not the same for every town. In some it is 25 ; in others it may be as high as 100. The alternating current is very suitable for cautery heating and for lighting lamps, and for stimulation of the body. It is necessary for diathermy. It cannot be used for ionisation or electrolysis or for operating induction coils. As with the direct current, the first requirement is the STATIC TRANSFORMER 47 reduction of the voltage and amperage when it is to be appHed to the body. This may be done by a shunt resistance as described for the direct current, but a much more satisfactory way is to use a " static transformer." By means of this the current from the main and that passing to the patient are quite separate from each other, so that risks of shocks from short-circuiting are not possible. Regulation of the strength of the current pass- ing to the patient can then be easily effected by inserting AUfi-TTW-ttvig Correut Main pjACMt Fig. 23. — Scheme for derivation of current from alternating current main by way of a transformer, and regulation of current by means of a resistance either in shunt (R^) or in series (R^). a shunt resistance or series resistance in circuit with the patient. A scheme of the arrangement is shown in Fig. 23. A static transformer consists of a core of soft iron, around which are wound two separate coils of insulated wire. One of these coils is called the primary coil, the other the secondary. These coils form quite distinct and separate circuits. The alternating current from the main passes through the primary coil, and as it oscillates to and fro induces another alternating current in the secondary. It is not possible, with proper insulation, for the main current in the primary coil to get into the secondary 48 ESSENTIALS OF MEDICAL ELECTRICITY coil. The voltage and amperage of that induced in the secondary depends upon the number of turns of wire in this coil, as compared with the number of turns in the primary. If there are fewer turns in the secondary, the induced current will be of lower voltage and higher amperage (suitable for cautery and lamps) ; if there are more turns in the secondary than in the primary, the induced current will be of higher voltage and lower amperage. This transformer is called a 5^/zc trans- former, as it has no moving parts, unlike the motor transformer. A static trans- former suitable for deriving a current for cautery and light is shown in Fig. 24. The transformer is fixed to the upper rr. r r X . , , ^ P^rt of thc board. Fig. 24. — Transformer for JLight and Cautery ^^ ,. ^ ^ The alternatmg current , taken from a lamp-holder or wall plug (the primary coil of the transformer takes a current of about 2 amperes), passes to the primary coil of the transformer. On the secondary coil is wound a smaller number of turns of wire so that a current of lower voltage and higher am- perage (also alternating) is induced in it. This current which is suitable for heating cautery and has an am- perage of about 18, is led to the two terminals on the bottom left-hand corner of the board. There is another secondary coil also wound over the primary, and the number of turns is arranged so that a SINUSOIDAL CURRENTS FOR TREATMENT 49 current of about 2 amperes at 15 volts is induced in it. This current is suitable for lighting lamps. It is led to the terminals at the bottom right-hand corner of the board. The cautery current and the light current may be regulated according to the requirements of the instru- ment or lamp used. The regulation of each current is effected by a "rheostat " (a variable resistance). Each rheostat is made of a coil of resistance wire, and a variable length of it can be included in the circuit (in series) by altering the position of the slider. The upper rheostat is for the cautery current, the lower for light current. For both of these currents the voltage has been lowered. The transformer is therefore known as a " step-down " transformer. A sinusoidal current suitable for use in electric baths can be also obtained from a static transformer. The secondary of the transformer is wound so that the voltage of the induced current is high enough to overcome the resistance of the baths in the circuit. Usually it has to be raised ; the transformer is then a " step-up " trans- former. Regulation of this induced current can be effected by means of a shunt resistance of the same kind as that used for lowering the voltage and amperage of the direct current from the main (described in the early part of this chapter) or by a series resistance. Another way of regulating the current is to lead it through a coil of wire, like the primary of an induction coil, and let it induce another current in a separate coil that can slide over the primary as a sledge (like the secondary of an induction coil). This last current is taken to the patient and its strength can readily be regulated by sliding the secondary over the primary. By means of a motor the secondary can be made to slide backwards and forwards over the primary, and so produce rhythmic variation of the current supplied to the patient. A device of this kind, made by Gaiffe, of Paris, r 50 ESSENTIALS OF MEDICAL ELECTRICITY has been in use in the electrical department at St Bartholomew's Hospital for some years, for supplying a sinusoidal current to three arm baths placed in series. It requires very little attention and there is no risk whatever in using it. For the purpose of electrolysis, ionisation, etc., for which an alternating current cannot be used, some method must be adopted for converting the alternating into a constant (direct) current. This can be done by means of a motor generator adapted so as to work when supplied by an alternating current. " Universal " apparatus is made so as to take an alternating current, and it will then provide the currents that have been mentioned under the description of the Pantostat. The direct current supplied by the Pantostat is not sufficiently strong for the operation of large induction coils for X-ray work or high frequency. For these purposes it is necessary to use a more powerml motor generator. For operating the diathermy machine an alternating current is required, and the voltage of this current should be 100 and the amperage not less than 10. The cables that are fitted to a house for ordinary lighting purposes would not take a current of this strength. It is therefore necessary to introduce cables into the house that can take 20 amperes. The alternating current cannot be used to charge accumulators on account of its repeated change of direction. There is a device known as the "Aluminium Rectifier " which will allow the passage of a current in one direction, but not in the other. If, therefore, it is included in the circuit of an alternating current, only those portions that pass in one direction will be allowed through, and the current will now flow only in one direction. It will, however, not be constant, but intermittent. ALTERNATING CURRENT RECTIFIERS' 51 The rectified alternating current can be used for many purposes for which continuous currents are necessary. For charging accumulators some authorities consider it superior to constant current, and as a result of consider- able experience the author is inclined to agree with this view. It will drive continuous current motors quite satisfactorily and can be adapted to operate large spark coils so as to give excellent results. It is not smooth enough for direct apphcation to patients. Rectifiers are of two kinds — chemical and mechanical. Chemical rectifiers depend for their action on the pecuHar property of aluminium in that it offers a very high resistance to the passage of a current when it is made the anode of an electrolytic cell, at the same time it offers no particular resistance when it becomes the kathode. A rectifier maybe made of a jar containing a saturated solution of ammonium phosphate in which are partially immersed, without touching, a rod of aluminium and another of iron. A current is able to pass through the solution from iron to aluminium, but not from the aluminium to the iron. By means of a small cell of this kind an accumulator can be charged direct from the alternating main and left going all night, and in that way the battery kept charged and always ready for use. It is impossible for this rectifier to get out of order under ordinary circumstances, and it is quite independent of any temporary interruption of the main current. They are made of various sizes, the larger of which can be used for large sparks coils and for direct current motors, as well as for charging accumulators. What is known as the Nodon Valve is a rectifier constructed on this principle. These rectifiers have to be made very bulky when currents of any magnitude are passed through them, otherwise they become very hot. 52 ESSENTIALS OF MEDICAL ELECTRICITY Mechanical Rectifiers, — These are really motor trans- formers of which the motor part is constructed so that it can be worked by an alternating current. A direct current is then generated. The makers of "universal apparatus " construct types that can be operated by the alternating current. The direct current which they give is suitable for direct application to the body, in baths, or by means of ordinary electrodes. It is not sufficiently strong for the operation of large spark coils, such as are used for the production of X-rays. For this purpose larger motor transformers of the same kind must be used. Dangers attending the Use of Currents derived from the Mains. — ^At this stage it will be well to point out the risks that are run when current derived from the main is used for medical treatment, and show how they arise and how they may be avoided. In all cases where patients are being treated by means of electricity derived from the street mains, there are certain precautions which must be observed to prevent accident. On account of the voltage and amperage of the main current, it is always possible to give unpleasant, even dangerous, shocks. Even if such an accident should not be attended with serious results, it is very disconcert- ing to all concerned, and patients sometimes strongly resent even slight shocks if they have not been warned beforehand. Carelessness in this respect leads to loss of confidence on the part of the patient, and possibly even the loss of the patient. To understand why it is possible to obtain shocks when the current from the main is used, even with a shunt re- sistance, attention must be paid to the way in which the current generated in the power station is distributed along the mains. A system of distribution known as the three-wire system comes from the generating station in the form of a three-wire cable. One of these is the HOW SHORT-CIRCUITING IS POSSIBLE 53 positive, another is the negative, and the third is neutral and acts as a common return to the others. All three are insulated from each other. The neutral is positive to the negative wire, and negative to the positive wire, and, by a rule of the Board of Trade, must be connected /O — cable (eorirLcO) ~ Fig. 25 to earth. Consumers are supplied from the neutral and one or other of the other two. The earth is a good conductor of electricity. Anything that is connected to earth by a conductor (" earthed " is the customary expression), such as metal water-pipes, radiators, electric- light fittings, streams of water coming from pipes (metal or rubber), stone floors, wooden floors when damp, is 54 ESSENTIALS OF MEDICAL ELECTRICITY therefore connected to one of the main cables (the neutral one). Now if the patient is in connection with the other cable he has only to touch any one of the objects named, or touch the operator, who is himself touching one, to get the current from the main through him. The same thing will happen if the patient has damp boots resting on a wet floor or on water-pipes or other earthed objects. It is therefore necessary that a patient under treatment should be so disposed that no conductor connected to earth is within his reach. The floor should be quite dry, and, if it is made of wood or stone, should be covered with some non-conducting material, such as linoleum. It must not be forgotten that water containing substances in solution (and therefore a conductor) may drip out from the damp pads and moisten the floor, and make its way between adjacent pieces of the non-conducting material covering the floor, thereby establishing an earthed contact for the foot to touch. In the diagram (Fig. 25) is shown a patient receiving treatment by a direct current taken from the main, with a shunt resistance interposed, as described in the early part of this chapter. Two of the main cables are seen under the ground, and one of these (the neutral) is connected to earth. Suppose that the first cable is positive, the neutral cable becomes negative to it. The + cable is insulated from everything. A shunt resistance, BA, and lamp are shown and are supposed to be in a room. When the main current is switched on it passes from the insulated -l- cable up into the room, through the lamp, then through the shimt re- sistance, BA, then back to the earthed negative cable. CDFE is the circuit that includes the patient (Pt.). Part of the current passes through this circuit. Let us suppose that the patient is earthed (touching a radiator or water-pipe or electric switch, or standing on a non- insulating stone floor, or a damped wooden floor ; or he HOW SHORT-CIRCUITING IS POSSIBLE 55 may be touched by a friend who is earthed) . The current , instead of taking the path described, can travel through the lamp, along the shunt resistance as far as D,then to the patient at F, then through the patient to earth and the negative cable. But no shock will be felt, because r^ — coble (eaTTkfid) ^ Fig. 26 the resistance of the patient is probably not less than that of the portion of the shunt resistance, DC, which the current has avoided. But when D is placed closer to B, a shock will probably be felt. Now suppose that the current from the main is taken to the shunt resistance in the opposite direction. This may readily be done by altering the position of the two-point plug that leads 56 ESSENTIALS OF MEDICAL ELECTRICITY the current to the shunt resistance. Reference to the diagram shown in Fig. 26 shows that a short circuit will be formed through the patient if he is earthed and he will then receive the full pressure of the current from the mains. The current will pass from the positive cable to A, along CE to the patient, pass right through his body to earth, missing out the entire length of the shunt resistance, AB, and the resistance of the lamp. Such an accident could be prevented by making the plugs so that they can be fixed in only the correct position. It is safer to have two resistance lamps instead of one, and place the other on the other side of the shunt resistance, so that the current has to traverse it before entering the former at A. An additional precaution, which should always be taken, is to make the current pass through two lamps that are permanently in position on a switch- board on the waU before entering the other lamps and shunt resistance. It is always advisable to use two lamps, because if the filament fuses the metal may fall across and make a short circuit at the base of the lamp, and so cut out most of its resistance. If there is only one lamp, the sudden increase in the strength of the current passing through the shunt resistance and the patient would cause a shock. There is another possibility of accident, as the resistance wire may break, and if the breakage occurs between A and D (Fig. 25) the current must aU traverse the patient to get back to the negative cable. The shock that the patient receives is not likely to be severe, unless there is a greater length of wire included between A and D. This risk may be almost completely avoided by using two shunt resistances con- nected in parallel, so that the current traverses both simultaneously. If the precautions mentioned above are taken, the direct current from the main may be used for application to the body, either by means of pad electrodes or the AVOIDANCE OF DANGERS IN BATHS 57 Schnee bath. Accidental shocks, though disagreeable, are never fatal, because the current is applied only to relatively small portions of the body. In the case of the full-length bath the case is different. Here the patient is quite devoid of any protection which a dry skin or clothing might otherwise afford him, and is also quite unable to help himself quickly when immersed in the water of the bath. If it is desired to apply the direct current from the main to a full-length bath, the pre- cautions already mentioned have to be taken, and, in addition, the bath itself must be completely insulated from earth. To thoroughly insulate the bath is practically impos- sible in the case of those already fixed, but it is quite feasible if the bath is installed with that end in view. The one at the London Hospital was done this way and is satisfactory. The bath itself is of porcelain. Large rubber pads about one inch thick are placed between the bath and the cement pedestals upon which it rests. Part of the waste-pipe consists of a length of rubber hose — leakage of current may occur here along the thin layer of water left in the pipe, but its resistance is high enough to prevent any such leakage worth troubling about. The water-pipes are kept clear of the bath and discharge from a point high up out of the reach of the patient. The late Dr Lewis Jones considered that "no method which depends for its safety upon the maintenance of insulation from earth of a bath containing water is good enough to risk." If it is desired to use the direct current from the main in the full-length bath, the safest way is to use the motor transformer like that suppHed on the " Pantostat," etc. Motor transformers that are used for this purpose must have the wire of the armature of the motor quite separate and perfectly insulated from that in which the direct current is generated. At St Bartholomew's the direct current is not supplied 58 ESSENTIALS OF MEDICAL ELECTRICITY to any of the fuU-length baths, the alternating (sinu- soidal) current being used instead. As explained before, the inclusion of a static transformer removes all risks of short circuits to earth. After the current has been switched on and regulated, the patient requires no further attention. There has been no accident or failure since the baths were first installed. Another advantage of this freedom from risk is that continued attention to the patient while in the bath is not necessary — an advantage which is specially to be considered in busy hospital practice. Supply from Private Installation. — ^Where current from the main is not available some other source of supply must be sought. If it is intended to use electricity more or less exten- sively, of course the best way is to install a dynamo and drive it by means of a gas, oil or steam engine, or even a water turbine, if such power is available. The current could be used direct, but it would be found more con- venient to charge accumulators with it and use the current from them. In this way the engine need only be run for a few hours on two or three days a week, and the current will be available at all times. Where space is a con- sideration, a very compact little plant can be obtained, composed of a petrol engine, such as used on motor bicycles, coupled direct to a dynamo suitably designed for the purpose. A set to give 15 amperes at 60 volts meets most medical requirements in a private practice or small hospital, and runs very satisfactorily. In all cases the dynamo should be provided with sUp rings, so that alternating current can be obtained when necessary. While the upkeep of a small private plant as above indicated is not very costly, the initial outlay may prove an insurmountable obstacle. If there is a place in the SUPPLY FROM ACCUMULATORS 59 neighbourhood where cells can be charged, then accumulators should be used. Supply from Accumulators. — ^The construction and mode of action of accumulators is described on page 270. Accumulators provide a current of low voltage and high amperage, and are therefore particularly suitable for heating cauteries and lighting lamps. They can be readily obtained, packed in portable cases. Two to four connected in series will be sufficient for cautery and light ; and six will provide a current strong enough to work a spark coil as well. The strength of the current that is required can be adjusted by a rheostat attached to the case. The current from accumulators can be used for applications to the body, but as a higher voltage is necessary to overcome the resistance of the body, a number must be connected in series. The weight of such a battery would be very heavy ; it is therefore more usual to use a battery of dry cells when a direct application of the current to the body is to be made. Such a battery is described in the next paragraph. A dozen 4- volt batteries such as used for motor bicycles, could be arranged to meet most medical requirements by means of a multiple switch, which would put them all in parallel, for cautery or light, and all in series for direct application to the body — with a shunt resistance. Another method of utilising the high pressure direct current mains is to charge an accumulator therefrom through a resistance and then use the accumulator independently. This system has many advantages for certain purposes. It enables one to keep a battery charged which can be taken about and used for cautery, light, or working an X-ray coil. With the direct current laid on, the charging of a battery is most simple. A special plug is provided which is fitted with a lamp- holder so that lamps of different resistance may be used. 6o ESSENTIALS OF MEDICAL ELECTRICITY From this plug runs a double flexible conductor. Having ascertained which one of these is positive it should be marked so as to avoid confusion in the future. This end must always be connected to the + terminal of the battery and the other one to the - terminal. A i6 c.p. lamp should be placed in the lamp-holder and the plug inserted. The accumulator may be connected up to the main when the day's work is done and left going aU night when suflicient energy will have been stored up to last one or more days according to the demand made upon it. As the resistance lamp used glows with almost its full candle power there is no reason why it should not be arranged to take the place of one of the lights regularly used in the house. In this way the charging of the accumulator costs practically nothing. Supply from Primary Batteries. — If none of the sources previously mentioned are available, the supply may be obtained from primary batteries. Dry ceUs are now almost always used. Batteries of these cells packed away in wooden cases are now extensively used, and by reason of their portability, cleanliness and freedom from risk of shocks by short-circuiting to earth, are convenient for those for whom a main supply of current is not available. The cells wiU last for two years with average use before they require to be replaced by fresh ones. . Primary batteries of dry cells will provide a current suitable for application to the body, as for electrolysis, ionic mediation, etc., and for the lighting of smalllamps. The amperage of the current is not sufficient for heating cauteries or driving spark coils for X-ray work or high frequency. For these purposes batteries of bichromate cells (page 272) are suitable. Such batteries can now be obtained in portable cases. They are heavier than the dry-cell batteries and require more frequent recharging. DRY CELL BATTERIES 6i although the owner can recharge them himself if he has a stock of potassium bichromate and sulphuric acid. Portable Dry Cell Batteries. — ^These batteries can be obtained from any instrument -maker. The number of cells that they should contain will depend on the purpose Fig. 27 for which the current is required. For application of the current to the mucous membranes, 8 to 12 will be enough. For application to the skin, a larger number will be required. A battery of 32 will be suitable for almost all cases for which the direct application -of the galvanic current to the body is desired. Fig. 27 shows such a battery. The case also contains a milUampere- meter, a current reverser, and a current collector. By 62 ESSENTIALS OF MEDICAL ELECTRICITY means of the latter, the strength of the current can be increased or diminished by including a larger or smaller number of cells in the circuit. It consists of a metal arm pivoted in the centre of a disc upon which are arranged as many studs as there are cells in the battery. These studs are insulated from each other and arranged in a circle, so that the metal arm as it is rotated comes successively into contact with the Fig. 28 studs.^ The ceUs are all joined up in series, but a wire has to be brought from each junction to one of the studs, to which they are joined in regular order. In this arrangement the first cells are always used, those at the other end are used only when the strongest current is required. Hence the first cells are exhausted soonest, and then they form a useless resistance for the other cells to traverse. The double collector. Fig. 28, is an improvement on DRY CELLS AND SHUNT RESISTANCE 63 this, enabling any group of cells to be used at will. It has two cranks mounted on the same axis but insulated from each other. One crank is connected to the positive and the other to the negative terminal. An index is fitted to one of the cranks which shows at a glance the number of cells in action at any moment. Next to the shunt resistance it is the best method of controlling the current from a battery of this kind. The current collector does not allow absolutely even regulation of the current. The current increases step by step as cell after cell is taken into the circuit ; these sudden increases cause pain when sensitive parts, such as the alveoli of the teeth, are subjected to them, but are not felt when the current is passed through the skin in less sensitive parts. A shunt resistance allows the most perfect regulation of the strength of the current. The cells are joined together in series and the current from the total number is passed through a rheostat. The current for the body is shunted off from the rheostat and its strength is regulated by moving a slider along the latter, the method being the same as that adopted for the regulation of the drect current from the main. CHAPTER IV THE BODY AS A CONDUCTOR OF ELECTRICITY Resistance of the Body. — ^When an electric current traverses the body, it encounters its chief resistance in its passage through the skin, the soft tissues and organs underneath opposing its flow to a much lesser degree. The resistance of the skin var'es within wide limits, while that of the underlying parts is relatively constant. The explanation of these facts will be apparent when it is remembered that the conductivity of the tissues is due to the presence of ions. The skin is poor in ions, their number varyiag considerably, according to the condition of the skin ; the underlying tissues and organs contain abundance of ions, and their proportion is relatively constant. The outermost layer of the skin is the horny layer, and if it is quite dry, and if the electrodes in contact with it are dry metal, there will be no ions to conduct the current through the skin. If this current is the constant current and at a voltage not higher than that at which it is usually applied for medical purposes (say '50-70 volts), it will be unable to overcome the resistance of the skin and no current wiU flow. If, however, the sweat glands secrete, the dry skin will be moistened and contain ions, and some current will flow. If the skin is moistened with salt solution, as is customary before applying the elec- trodes, its resistance is artificially reduced, by reason of the diffusion into the horny layer of water containing ions. The resistance and the body will vary also according 64 RESISTANCE OF THE BODY 65 to the size of the electrodes ; if the latter covers a large area of skin there will be a large area of entry for the current and the resistance will be lower. The distance between the electrodes will also influence the resistance ; the longer the path for the current, the greater the resist- •ance, and vice versa. It wiU be seen, then, that the resistance of the body depends upon a number of factors and can vary within wide limits. If the constant current is used and is sent from one hand to the other, along the upper extremities and across the trunk, the hands being immersed in salt solution, the resistance may be taken as about 1300 ohms. When the resistance of the skin is excluded, the residual resistance is much less. Some experiments by Weiss showed that the resistance from shoulder to shoulder was 40 ohms, and from elbow to elbow was 250 ohms, when the skin resistance was excluded. If the current is allowed to flow for some time and the metals of the electrodes be separated from the skin by pads soaked in salt solution, ions will actually migrate into the skin, and the resistance of the latter will pro- gressively diminish, till it reaches its lowest value at the stage when it is permeated with ions. The phenomenon wiU be frequently observed during the process of medical ionisation ; the needle of the mHUampere-meter will be seen to move gradually across the scale, showing that the strength of the current is increasing owing to the diminu- tion of the skin resistance. If, however, the moistened pads contain ions that will form insoluble compounds when they come in contact with ions in the skin, the reverse will take place ; the needle will move in the opposite direction, showing a fall in the current strength. The resistance of the skin has increased because the number of ions in it has diminished. The thick skin of the pahns and soles has a higher resistance than the thinner skin elsewhere. Patients 66 ESSENTIALS OF MEDICAL ELECTRICITY who have been long confined to bed have a high skin resistance, because the horny layer is less readily shed and therefore thicker. The body offers less resistance to currents that are alter- nating or intermittent, flowing for very brief periods in any one direction before interruption or reversal. Thus the re- ' sistance of the body is much less for f aradic currents, and currents that alternate with a high frequency. The writer has measured the resistance of some hundreds of patients to the f aradic current, pre- vious to taking electro- cardiographic records, and has found it to vary, in different individuals, from 500 to 700 ohms. The resistance was taken from elbow to elbow, the forearms being immersed Fig. 29.— Diagram to indicate diver- ^ ^^^^ solution. The gent lines of flow of constant current faradic and alternating through tissues, with greatest density of currents do not alter the current immediately under electrodes, ^^^^entb GO noi aiier ine resistance of the skin like the constant current, because they do not cause a migration of ions into it. Path of the Current in the Body.— When the current has passed through the skin it encounters much less resistance in the underlying tissues. The path of least resistance will be the shortest path between the electrodes, and more of the current will pass that way, but some will take more circuitous paths, because, having a choice of several paths, it will distribute itself between them, the amount going by each one being inversely proportional PATH OF CURRENT IN BODY 67 to its resistance. Some of these paths will loop out to each side (Fig. 29) beyond the parts enclosed between the electrodes, and the amount of current flowing along these paths will be less as the loops become wider and the paths between the electrodes become longer. It will be evident then that the deeper a tissue lies the smaller will be the share that it will receive of the whole current passing between the electrodes. The density of the current (that is, the amount of the current traversing a unit of sectional area at right angles to its path) will be greatest at the points of its entry and exit, and least at a point half- way between. If we imagine the current of electricity to be made up of thin lines or strands, where the density is greatest they are gathered together as in a cord. If the cord is frayed out the density is less, but the same number of lines are there. In its passage from one electrode to the other no lines are lost, but some of them will take a very circuitous route before being finally gathered in at the other electrode. If one electrode is larger than the other the density will be greater at the smaller. A certain minimum density of current is necessary to produce appreciable physiological or therapeutical results, and one may safely say that with the currents used in medical electricity the density in the outlying regions away from the direct line between the electrodes is so slight as to be of no importance. If the electrodes are placed both on the same side of the trunk or a limb, the lines of flow of the current wiU Fig. 30 68 ESSENTIALS OF MEDICAL ELECTRICITY dip down into the deeper parts (Fig. 30), but the density of the current will be greatest under the electrodes and in the superficial parts, but very slight in the deeper parts. Very little current will travel in the skin itself between the electrodes on account of its high resistance. If the electrodes are placed on the same side, but farther apart, more of the current will flow through the deeper parts than if they are placed closer together (Fig. 31). It is important to remember the divergent path taken by the current between the electrodes. It explains why it is that a stronger current is required to stimulate a deep-lying muscle or nerve. Tissues that lie be- neath the surface receive only a portion of the whole current, and a portion that becomes progressively smaller the deeper they lie. The divergent path taken by the current is one of the reasons why ions cannot be taken, from without, into the deep-lying organs in sufficient number to be of therapeutic value. The milliampere-meter gives information of the total amount of current passing through the body, but not the amount passing through any one part of it. The divergent path that has been described is that taken by the constant current. It is probable that currents which oscillate with a high frequency do not take such a path, but confine their course to the part l5dng between the electrodes, without spreading to those lying on each side. Fig. 31 Anode and Kathode. — ^The anode is the electrode by ANODE AND KATHODE 69 which the current passes into the body (it may be remembered as the " in-ode ") ; the kathode is the electrode by which the current passes out of the body. In physiological experiments, in which we use excised muscle and nerve and place the electrodes in actual contact with them, the current is confined to them and there is one anode and one kathode, each locaUsed to the point of contact of electrode with tissue. In the case of the body the conditions are quite different, and it is impossible to place the electrode or electrodes in actual contact with the muscle or nerve which is to be stimulated. Anode Sorfr. M. zygimiatici K. orbicul. arte | Uiddit branch (ff facial H. leTatoT ment; M. qoadr. menti X. triaog. menu [Mter brunch offaeiaX M. pUtysma mjold. Hyoid muicles | U. omohyotdeos Ant. thoraeU «i (M. pectoial.) Eegion of Snl frontal con-T. and island of Bell (centre for HL temporalis forfain, (trunk) Pott, aurkvlar n. Middle branch of facial Lower branch (^facial K. spleniM U. gtemocleido- inaktoideus !^^tmiU aeeeuory n. SC l«Tato» angnli scapoL Long thoracic n. ( M. eerrat.aat.B«j.) Phrenic n. Si^raeleaiicular point. Brachial plexui. (Erb 8 point. H. deltoid., biceps, brachialia intern. And sapJi. long.) Med. Elec PLATE II ]|.latenMa.domLI. •tU. trioep3(c>4>at PLATE III M. triceps (long head) U. triceps (inner bead) Dinar h, | If. flexor car})I ainaria M. flex. i1if;ltor. commun. prufuud. :. flex, (ligitor. snblim. (digiti II. ct lU.) , flet. digit, siubl. (digit indicia et miniuii) M. polnuuris brev. M. abductor digiti niin. M. Oexor digit, min. U. opponens digit, min. Mm. lOMbrlcales ^ li. bleeps bxmcbb M. abdactor pollia I M. opponeni poUiois VL flex. poll. breT. M. adductor pollic. brer. Med. Elec* PLATE IV CrunUn. it. iMlductor magnns U. adduct. longos M. vastus internus M. tcusor fosciiB lata li, quadriceps fctnorU (common point) M. rectus femorls M. castas eztcrniu PLATE V U. tibiaL antio. U. cxtecs. digit, long. M. peronens breria M. extensor hollucia long. Xm. iatcronei don<t M. gastrocnom. extent. 21. peronctw lougtu U.aoIew M. flexor balluds louff. M. exteoa. digit, comtn. brevi» U. abductor 5th, supra-orbital branch 5th. auriculo temporal branch 5th. infra-orbital branch 5th. inferior dental branch Superficial cervical (cervical plexus) PLATE VIII. Supra-clavicular nerves Circumflex Musculo-spiral external cutaneous branch M uscuJo-cutaneouB Median Intercostal humeral Lesser int. cutaneous Internal cutaneous Ulnar PLATE IX Intercostal humeral Lesser inter, cutaneous Internal cutaneous Ulnar Supra-scapuiar Circumflex Musculo-spiral int. cut blanch Musculo-cutaneous Musculo-spiral external cutaneous branch Radial PLATE X Genito-crural External cutaneous— -\— Anterior crural middle cutaneous branch External popliteal External saphenous Ilio-inguinal Anterior crural (int. cutaneous branch) Anterior crural Aong saphenous branch) Musculo-cutaneous Anterior tibial PLATE XI Inferior gluteal f^nterior crural, internal cutaneous branch | i Post tibial - — External cutaneous Great Small Sciatic Ext. popliteal Ext. saphenoC CHAPTER XI HIGH-FREQUENCY CURRENTS A HIGH-FREQUENCY Current is one that periodically reverses the direction of its flow at an exceedingly high rate. A current may be made to reverse its direction any number of times per second, but when the frequency of reversal is sufficiently high the physical properties of the current and its action on living tissues are profoundly altered. The current is no longer able to produce chemical (electrolytic) changes in solutions of salts, nor is it able to evoke a response from the excitable tissues. The frequency of reversal may be called high when the current is unable to produce these chemical changes or to stimulate muscle and nerve to give their customary response. Such a frequency would be about a miUion times a second. How High-Freauency Currents are produced. — ^A con- tinuous current may be made to reverse its direction periodically by means of a simple apparatus known as a current reverser or commutator. No mechanical apparatus of this kind can produce a sufficiently high frequency of reversal, and the current is generated on quite a different principle. If a condenser, such as a Leyden jar, is charged and then discharged, the current that flows during the period of the discharge, though of momentary duration, will be a high-frequency current if certain requirements are fulfilled in the circuit along which the discharge takes place. The resistance of the circuit must not exceed a L i6i i6z ESSENTIALS OF MEDICAL ELECTRICITY certain value. In the second place, the circuit must be arranged so that self-induction (page 287) can take place along it. Both these requirements will be satisfied if the circuit is constructed of a thick copper wire bent in the form of a spiral. If the discharge takes place along Fig. 44. — D'Arsonval's Transformer such a circuit, the current that traverses it will flow or oscillate backwards and forwards from one coat of the condenser to the other, getting successively feebler with each reversal till it dies away. At this moment the con- denser is discharged. All this takes place in a very brief period of time, its duration depending on the capacity of the condenser, and the resistance of the circuit and the HIGH-FREQUENCY APPARATUS 163 amount of self-induction that takes place in the circuit. If these factors are known the number of oscillations per second (i.e. the "height" of the frequency) can be calculated. Apparatus for the Production of High-Frequency Currents. — ^The arrangement of Leyden jars and wire ■OFO i—5 mmm Fig. 45. — Plan of High-Frequency Arrangement Spiral is shown in Fig. 44, and the plan is shown in Fig. 45 and is known as a d' Arson val transformer. It is named after Prof. d'Arsonval, of Paris, the pioneer worker in high-frequency currents in their physiological and medical application. It is a simple device for converting or transforming continuous currents or i64 ESSENTIALS OF MEDICAL ELECTRICITY alternating currents of low frequency into others of high frequency. In Fig. 45, C and D represent the condensers (Leyden jars) in section, each with its outer and inner coat and the intervening insulating material (glass). The inner coatings are connecting to the terminals of an induction coil. The outer coats are connected by the wire spiral, E. This spiral is made of twenty turns of thick copper wire. It is known as the " solenoid." Sometimes a movable handle is fitted so that the number of coils included between the outer coatings of the jars may be varied. Sliding rods with a ball at one end and an ebonite handle at the other are attached, one to each metal pillar that makes contact with the inner coating of each jar. The space between the baUs is the " spark-gap," and it can be varied by sliding the rods to or from each other. The jars may be charged from a static electrical machine, or from an induction coil. The usual source is a large induction coil of the type used for X-ray work. When the induction coil is used we are really deriving our supply from a constant current (taken from the mains or a battery), and the induction coil serves to transform this current, raising its voltage to the necessary degree. The alternating current from the mains may also be used to charge the jars after its voltage has been raised suitably by a static transformer. When the in- duction coil is set in action and the spark-gap sufficiently narrowed a torrent of noisy sparks darts across the gap, and at the same time the solenoid is traversed by high- frequency currents. The following events take place. The inner coats of the jars are charged, one positively, the other negatively. Charges of opposite sign are induced on the outer coats. The charges on the inner coats neutraUse each other by sparking across the gap and simultaneously the induced charges on the outer coats neutralise each other and a momentary current passes along the solenoid. INTERMITTENT OSCILLATIONS 165 This current is a high-frequency current, because the solenoid has a low resistance and allows sufficient self- induction to take place. The sparks that appear at the gap seem to follow each other without intermission, and hence it would appear that the charging and discharging of the jars are continuous, giving rise to sustained high-frequency currents along the solenoid. This, however, is not the case. The jars are charged only at the moment when the " break " current is induced in the secondary wire of the coil. They are therefore charged not continuously but intermittently, the actual number of times per second depending on the Fig. 46. — Intermittent Trains of Oscillations a to b — Train of oscillations, lasting ^ sec. b to c — Intermission, lasting y^g- sec. c to d — Next train of oscillations rate at which the interrupter makes and breaks the cur- rent suppUed to the coil. Suppose that this rate is 100 per second. Each tw^^ ^^ ^ second the jars are charged and discharged, giving rise to a high-frequency current in the solenoid. But the jars take a much shorter time than yjo^h of a second to completely discharge. It may be taken, for jars of the capacity used in the d'Arsonval transformer, as -_i-- th of a second. It follows that every 5 0,0 00 "^ yi^th of a second a train of high-frequency oscillations lasting g^^^^ traverses the solenoid. The high-frequency current as suppHed by the d'Arsonval transformer is, therefore, intermittent, short trains of oscillations separated from one another by very much longer intervals of rest. It may be represented as shown in Fig. 46. i66 ESSENTIALS OF MEDICAL ELECTRICITY Although the actual resistance of the solenoid to a direct current is extremely low, its resistance to the high- frequency current is very great, even though the potential difference between the outer coats of the Leyden jars is very high, amounting to many thousands of volts. This is because the wire of the solenoid is bent in the form of a spiral with closely adjacent coils so that other currents are induced in the same circuit. It will be remembered that the moment a current begins to flow alongaspiral, another current is induced in the same circuit and flows in the opposite direction and impedes it. The in- duced current is only of momentary duration, so that its only effect on the other current is to impede it at its commencement and so retard its rate of growth to its maximum. But if the inducing current lasts only for the same brief period as the self- induced current it will be opposed considerably and prevented from growing to its full strength. The high-frequency current flows only for a moment in one direction before it reverses, and it is therefore greatly opposed by the currents it induces in its own circuit. If a straight wire connects the ends of the solenoid the high-frequency current will travel by preference along the former, even if it has to spark across a small air-gap in the circuit, and so overcome a high resistance. If the high-frequency current is to be applied to the body it is led off from the termina- tions of the solenoid by means of suitably insulated cables. Fig. 47. — Hot-wire Milliampere-meter HOT-WIRE AMPERE-METER 167 Measurement of High-Frequency Currents. — ^Alternat- ing currents, whether of high or low frequency, cannot be measured by the ampere - meter de- scribed later (page 283), because their direction is con- stantly reversing. The hot-wire ampere- meter may, however, be used for the pur- pose (Fig. 47). In this instrument the current is led through a fine wire, of high resistance. The wire is heated in propor- tion to the strength of the current, so that it lengthens to a corresponding de- gree. The degree of lengthening is indi- cated by a needle moving over a scale cahbrated so that a certain number of divisions correspond to a known current passing along the wire. The current sup- plied by the d'Arson- val apparatus may ^^^- 48-High-frequency Outfit reach a strength of 0*5 or o-6 amperes (500 or 600 milliamperes) when traversing the body. i68 ESSENTIALS OF MEDICAL ELECTRICITY A complete form of high-frequency apparatus is shown in Fig. 48. The various parts are mounted on a trolley. The Leyden jars are on the lower shelf ; in front of them is the spark-gap, enclosed in a glass cylinder to diminish the noise of the sparks. Above the jars is the solenoid. On the top of the trolley is the " resonator " (see later, page 170). How High-Freauency Currents are applied to the Body.— (i) The Direct Method. — The extremities of the solenoid are connected to electrodes placed in direct contact with the skin. The electrodes are made of sheets of pUable metal, such as copper, lead or tin cut to suitable sizes. They are placed in contact with the previously moistened skin and secured in position by a bandage or sand-bag. The metal should make even contact all over. Instead of placing the metal in direct contact with the skin, a pad of absorbent material, such as Unt, soaked in salt solution may be interposed. Its thickness should be that of eight layers of lint, and its area should be slightly larger than that of the metal plate. It is soaked in a solution of salt so as to enable it to conduct the current readily. The strength of the solution should not be less than 5%. The metal plates are connected to the extremities of the solenoid by thickly insulated cables. Of the electrodes, one is the cctive electrode and is placed on the part to be treated. The other is the indifferent electrode. It is of larger size than the active electrode and is placed on some convenient part, preferably on the opposite aspect of the body. A second active electrode may be used instead of the indifferent electrode and both placed on the part requiring treatment, one on one side, one on the other. (2) Indirect Method. — ^Instead of placing the indifferent electrode in direct contact with the body it may be placed a little distance away with the intervening space occupied AUTO-CONDENSATION COUCH 169 by some insulating material. Such an arrangement is seen in the "condenser couch" or "auto-condensation couch" (Fig. 49). This couch contains a long metal plate fixed under the upholstery and insulated from it. It is connected to one extremity of the solenoid. The patient Ues on the upholstery, and the other end of the solenoid is attached to a metal handle, fixed to the couch and grasped by the patient, or to an electrode placed on any desired portion of the skin. The couch is called a " condenser couch," Fig. 49. — Auto-Condensation Couch because the patient and the metal plate form the arma- tures of the condenser and the intervening insulating material the dielectric (see page 261 for description of condensers). The patient and the metal plate are alternately charged and discharged with a frequency corresponding to that of the oscillation of the current. The current surges to and fro and into and out of the patient, so that the whole body is brought under the influence of the current, and thus receives general treat- ment, while that part of the body in contact with the electrode receives the greatest concentration of the current, and so gets local treatment. The condenser couch method, or " auto-condensation " 170 ESSENTIALS OF MEDICAL ELECTRICITY method as it is sometimes called, therefore enables both general and local applications to be made, while the metal electrode under the couch obviates the necessity of fixing an indifferent electrode in contact with the skin each time the treatment is given. Another way of giving general applications of high frequency is to enclose the patient within a greatly enlarged solenoid. The patient stands or sits within the solenoid, the long axis of which is vertical. He does not come in contact with any part of it. His body is traversed by " eddy " currents that are induced within from the coils of the solenoid. This method of applica- tion is known as the " auto-conduction " method. There is a method of applying high frequency specially suitable for local applications. If one of the electrodes attached to one end of the solenoid is placed in contact with the body and the other (the active) electrode be brought near to the skin without actual contact, a dis- charge of sparks will take place across the intervening space. If the active electrode terminates in a metal point or group of points, the discharge takes the form of a brush of very fine sparks or " effluve." To procure an efficient eftiuve it is necessary to have a considerably higher voltage between electrode and skin than that reached between the extremities of the solenoid. By connecting to one end of the solenoid an additional coil of wire, and attaching the active electrode to the free extremity of this coil, the voltage will be considerably raised. This additional coil is known as " Oudin's resonator." It is shown in Fig. 48, where it is seen mounted vertically on the top of the trolley, partly enclosed in an insulating cover. It consists of a wooden cylinder or cage about nine inches in diameter, and fifteen to eighteen inches high, and wound with about sixty turns of moderately coarse wire — the individual turns are about one quarter of an HIGH-FREQUENCY EFFLUVE 171 inch apart and should be evenly spaced at all points. The lower end of this wire is joined to some part of the thick wire spiral (solenoid) of the high-frequency- apparatus, the best point being found by experiment. The upper end of the resonator terminates in a knob mounted on top of the instrument. The wire of the resonator acts as a continuation of the solenoid. It is possible to dispense with the latter and use the lower few turns of the resonator in its stead. If this is done, the lower (proximal) end would be connected to the outer coating of one jar, while the outer coating of the other is attached to a point a little higher up, changing it about until the best effect is produced. To the upper (distal) end of the resonator is attached an insulated cable and to the free end of the latter is secured the electrode. When the apparatus is set in action a profuse " brush discharge " or effluve is given off from the electrode. This effect is increased when one end of the solenoid — or, when this is not used, the lower end of the resonator winding — is connected to earth, by attaching it to a gas or water pipe. The length of the effluve depends upon the point along the spiral to which the outer coat of the second Leyden jar is connected, and a slight alteration in the position of this point may considerably increase the length of the effluve. For local applications, many forms of electrodes have been used. The simplest is what is called the brush electrode, and consists of a metal plate from one to three inches in diameter and studded on one side with a number of sharp metallic points or tufts of fine brass wires or tinsel : to this metal plate is attached an ebonite rod for the operator to hold. Other forms are made of closed glass tubes, either filled with some conducting liquid as water or saline solution, or exhausted until the partial vacuum produced becomes sufficiently conducting. They are sometimes 172 ESSENTIALS OF MEDICAL ELECTRICITY caUed condenser electrodes, because the internal conduct- ing medium induces, when charged from the resonator, corresponding charges on the outside of the glass. / The most generally used condenser electrodes are the so-called " vacuum " electrodes (Fig. 50). These are closed glass vessels of various shapes and sizes, from which the air has been sufficiently exhausted to render the residual gas as good a conductor as possible. One end of the tube is pierced by a platinum wire fused into its wall. To this wire is attached the cable from the Fig. 50. — Vacuum Electrodes resonator or solenoid. The other end of the tube is applied to the patient. When the current is turned on the air within the tube conducts the current and becomes incandescent, glowing with a violet-blue light. At the same time fine crackling sparks pass from the glass at the end in contact with the skin. The sparks are longer if the electrode is attached to the resonator than if it is attached to the end of the solenoid. Of all the ways of applying high-frequency currents, the local application of the current from the top of the resonator is perhaps the most successful. It may be applied in the form of a soft brush discharge from a multiple point electrode held just so far from the patient that actual sparks do not pass. There is a copious HIGH-FREQUENCY ELECTRODES 173 production of ozone and the brush itself acts as a mild stimulant. Instead of this we may use a vacuum elec- trode which is of glass and placed in contact with the surface to be treated. The strength of the appHcation can be very gradually adjusted, and, speaking generally, it is more stimulating than the brush. In some of these electrodes the vacuum is so high that X-rays are given off in small amount, but it is doubtful if such rays exist in sufficient quantity to have any effect. The appUcation from a vacuum electrode can be made so strong as to be decidedly painful and produce blistering if kept on too long. If such vigorous treat- ment as this is required it is better to use a plain metal point electrode, owing to the fact that the glass electrodes tend to become pierced under such conditions, and so rendered useless. In use the metal point is held a little way off the surface to be treated, so that the spark has to jump across a gap the length of which is limited by the strength of the current employed. The rule is, the farther the point from the skin the more severe and painful is the effect. If the point is held very close and a strong current turned on, the local effect seems to be to a great extent a thermal one and a small blister quickly forms — as we withdraw the point the character of the discharge changes, becoming more intermittent, more painful and disturbing to the patient, and the effect seems to influence the tissues some distance down — superficial muscles are thrown into contraction and the skin takes a " goose skin " appearance — later on the part becomes red and blisters form. This method can be carried out by any high-frequency arrangement and wiU be found very useful in the treat- ment of warts, acne vulgaris, and port wine marks. 174 ESSENTIALS OF MEDICAL ELECTRICITY The Action of High-Frequency Currents on the Body. — High-frequency currents produce none of the sensations that are customarily associated with the passage of electrical currents. Although the high-frequency current may reach a magnitude of 500 milliamperes or more, there is no contraction of muscle, no perception of pain or tingling. The only sensation that is apparent is warmth, and this is, as a rule, sHght and not immediately perceived. We have now a satisfactory explanation of this appar- ently anomalous behaviour of electrical currents when they oscillate at an extremely high rate, and the matter has been considered in Chapter I., dealing with the mode of action of electricity on the body. It may be mentioned here that it is the movement of ions caused by the current that constitutes the electric stimulus and that the high-frequency current oscillates to and fro at a rate so high that the ions are unable to keep pace with it. There is therefore no movement imparted to them by the current, so that the latter is unable to stimu- late the tissues. High-frequency currents can, however, bring about physiological and therapeutic effects, and the question arises, " What is the mode of action of these currents in bringing about the effects observed ? " Most probably by the production of heat. There is an actual sensation of heat in the skin, and it may be measured by a surface thermometer. The heat becomes greater as the area of contact between the electrode becomes smaller, thereby increasing the density or "concentra- tion " of the current at its entry, and it may actually cause a burn if the electrode has the form of a wire or needle. The development of heat within a conductor by an electric current in proportion to the resistance of the conductor and the square of the strength of the current is a well-known physical law (Joule's law). In the case of high-frequency currents and the body, we have a HIGH-FREQUENCY CURRENTS 175 conductor of sufficiently high resistance and a current of sufficient strength, and when the current traverses the tissues heat is developed along its path, both on and within them. The development of heat on the tissues, " epithermy," can be readily demonstrated. The de- velopment of heat through the tissues, " diathermy," is less easy to demonstrate, as the currents produced by the commonly used d'Arsonval type of high-frequency machine are not very strong, and its density diminishes as it penetrates the tissues. But it is a necessary con- sequence of Joule's law that heat should be developed within the tissues as well, and it can be shown when stronger high-frequency currents (as generated by the diathermy apparatus described in the next chapter) are used. High-frequency currents have for the past twenty years been used empirically, with varying degrees of success for many maladies. When this form of electrical treatment is to be appUed, its mode of action by the production of heat on and within the tissues should be borne in mind, and the question of the advisability of its application and of the Ukelihood of benefit re- sulting should be considered from the same point of view. High-frequency currents have the effect, when the whole body is brought under their influence, of increasing the metabolic changes. D'Arsonval showed that there was an increase in the output of carbon dioxide, of nitrogen and phosphates in the urine, and an increased output of heat. This is what might be expected to follow a gentle warming of the tissues. High-frequency currents have an influence on the vascular system. Sloan found that their first action was to produce a peripheral vaso- dilatation. The heart then beat more rapidly and counteracted the tendency to fall of blood pressure produced by the vaso-dilatation. 176 ESSENTIALS OF MEDICAL ELECTRICITY When local applications are made with the vacuum electrodes, no sensation other than that of heat is pro- duced, if the glass is in contact with the skin ; when it is placed a short distance away, numbers of sparks leap across and produce a pricking sensation. The skin soon acquires a vivid erythema, and if the application is for more than a short time in one situation localised burning may result, especially if the current is strong. The application of the effluve produces the feeling of a warm breeze, which may become uncomfortably hot when the electrode is placed near to the body : if brought very close, sparks will pass and cause pain. The effluve also produces an erythema of the skin. The stimulation of the skin and the erythema are the result of heating of minute points on which the effluve or sparks fall. There is at the same time a production of ozone and oxides of nitrogen from the atmospheric gases. These gases penetrate for a short distance into the outer skin layer, or they may possibly be formed there. Their odour is perceived for a considerable time afterwards. The therapeutic action of this local appUcation of high frequency is probably the result of local heating and the resulting hyperaemia. Possibly the new gases formed may have some action, particularly when the treatment is applied to infected ulcers and to cutaneous affections, such as acne and sycosis and others. High-Freauency and Surgical Cases. — ^It has been mentioned that the high-frequency sparks may produce destruction of the skin. They are actually used for the destruction of abnormal tissue. Metallic electrodes are used and sparks are directed from them on to the part to be treated. The destruction is brought about by the heat at the points on which the sparks fall. The tissue to be destroyed must be superficial and mlist not extend deeply. This form of treatment has been used with FULGURATION 177 success for flat naevi, moles and warts, and it has proved successful in some cases of lupus and rodent ulcers. Malignant growths have also been treated by long high- frequency sparks from powerful apparatus ; the name of " fulguration " has been given to such treatment. CHAPTER XII DIATHERMY In the preceding chapter it was pointed out that the high-frequency current provided by the d'Arsonval type of apparatus was intermittent — that is to say, the oscilla- tions occurred in groups, each separated from the preced- ing one by a long interval during which there was no current. It was shown that the time occupied by each group of oscillations was very short, while the interval between each group was relatively very long, so that during any period of treatment the body was under the influence of the high frequency for only a very short fraction of the time. During recent years new types of apparatus have been designed for the purpose of producing high-frequency oscillations that are continuously kept up and not inter- mittent. With a current of continuous high-frequency oscillation the sensation of heat which, with the inter- mittent oscillations was slight or even imperceptible, becomes very pronounced and may be unbearable. The heat is developed along the path of the current, both in the superficial and deep parts. In recognition of this production of heat through the tissues as the essential action of sustained high-frequency currents on the body the word " diathermy " has been devised to describe this mode of electrical treatment. It may be said that all high-frequency currents produce some degree of diathermy, although the heat may not be perceptible or measurable. " High-frequency " treatment, as gener- ally understood, refers to treatment by the intermittent 178 PRODUCTION OF DIATHERMY 179 high-frequency current produced by the d'Arsonval type of apparatus, and the term " diathermy " is reserved for treatment by continuous high-frequency oscillations producing heat as the most conspicuous effect. Whether the high-frequency currents are intermittent, producing a trifling amount of heat, or continuous, producing a large amount, the therapeutic action, in both cases, is due to the same effect — viz. the production of heat on and within the tissues. Diathermy has also been called " thermo-penetra- tion " and " transthermy," terms which also express the result of the action of sustained high-frequency currents of sufficient intensity. The Production of Continuous High-Freauency Currents. — ^These currents are generated on the same principle as the intermittent high-frequency current, but the various parts of the apparatus are modified. Instead of Leyden jars, the condensers are made of several sheets of metal separated and insulated from each other by glass or paper soaked in paraffin wax. These condensers have a larger capacity than the two Leyden jars used in the d'Arsonval apparatus. They are charged from the main, not from an induction coil. The positive and negative cables from the main are not connected directly to the condensers, because the latter would then be charged only to the voltage of the main supply, and this, at its highest, is not sufficiently high for the condensers. The voltage has therefore to be raised. This is done by means of a static transformer. The static transformer is described in detail on page 294, but we may say here that it consists of two coils of insulated wire, both wound on the same iron core, but separately and not in connection with each other. One coil, the primary, is made of a few turns of stout wire. The secondary is made of several turns of finer wire. The i8o ESSENTIALS OF MEDICAL ELECTRICITY current from the main is led through the primary. Currents are induced in the secondary, and their voltage and amperage will depend on the number of turns in the latter. The voltage is raised to about 2000. The current from the main must be an alternating current, PriT»La.ry coil 0^ Tra-ns|-ormer Setondary CO»l oj Transjornrver ill St>ark <^ap ■ i CoacLe.nsers Higti jreoi/enc^ Circuit High jrt(^enty Circud (Steondoryj » 6 ^O 30 Terminals ^o Patient Fig. 51. — Diagram showing Circuits in a Diathermy Apparatus because a direct current passing through the primary would not induce currents in the secondary. If the main supply happens to be a direct current, it must first be transformed into an alternating current by means of a motor transformer. The current that is supplied to the primary of the transformer may reach, say, lo amperes, and the voltage at which it is supplied from the main DIATHERMY MACHINE CONSTRUCTION i8i is 100. The latter is raised to 2000, and to this voltage the condensers are charged. Now in the d'Arsonval apparatus there is a transformer (viz. the induction coil with its iron core, and primary and secondary windings), but the current is treinsformed to a much higher voltage, 30,000 volts or more, which is unnecessarily high. Further, the primary of the induction coil is supplied by a current of less amperage, and, being a direct current, must be interrupted. It will therefore flow inter- mittently. Consequently there will be a smaller amount of electric energy supplied to the primary of an induction coil by the direct current than to the primary of a trans- former by the alternating current. The different circuits in the diathermy apparatus are shown diagrammatically in Fig 51. The condensers are charged from the secondary of the transformer. They discharge across the spark-gap and the solenoid is traversed by high-frequency currents. The spark-gap is quite different from that used in the d'Arsonval apparatus. The discharge takes place, not between two metal rods, but between large metal discs that are very closely opposed to each other without actually touching. There are two of these gaps placed in series. The discs are made of copper and their opposing surfaces, between which the sparks leap, are faced with silver. Each gap is about 0-4 millimetre wide. The high-frequency current that is to be applied to the patient is taken, not from the solenoid directly, but from another separate coil that can be placed in close apposi- tion with it, and so receive high-frequency currents by induction. This latter coil is the secondary high- frequency coil. A hot-wire ampere-meter is included in the circuit containing the patient and the latter coil. When an alternating current from the main is supplied to the primary of the transformer, the condensers are i82 ESSENTIALS OF MEDICAL ELECTRICITY charged and discharged at an extremely rapid rate, far more rapid than that at which the Leyden jars in the d'Arsonval apparatus are charged and discharged. The discharge across iflHIE y^^ 4HHHIHE the spark-gap ^^^^B: J^W^ ^mmi ^^|P causes a crack- jBB^^^ rr^jH^HI ^HBi ling, hissing WKf mt^^mKEik sound. The * ** j_ sparks are, as it were, spread out over a large area, and instead of the bright, white, noisy sparks seen in the gap of the d' Arson val ap- paratus, a film of non-luminous blue light occu- pies the narrow gap between the opposing metal discs. If wires connected to the extremities of the secondary high- frequency coil are brought close to- gether a torrent of thick, white, noisy sparks passes between them. A diathermy machine by A. E. Dean is shown in Fig. 52. The transformer, condenser and high-frequency coils (primary and secondary) are enclosed within the case Fig. 52 Diathermy Machine by Dean PHYSIOLOGICAL ACTION OF DIATHERMY 183 that forms the body of the machine. The cover of the case is formed by a marble slab, on which are fixed the ampere-meter, the spark-gap, the handles for regulating the currents, a switch for cutting off the current supplied to the machine and terminals for leading the diathermy current to the patient. The spark-gap is covered by a U-shaped metal cage, so as to protect the operator from burns which might be caused by accidentally touching the metal discs. Other models of diathermy apparatus have been de- signed. They all work on the same general principle and differ chiefly in the method adopted for regulating the strength of the current and in the construction of the spark-gap. In the machine illustrated the high- frequency current is regulated by bringing the secondary high-frequency coil more or less closely in apposition with the solenoid. This is effected by rotating the handle shown on the right-hand side of the marble slab. A crank, shown on the left-hand side, regulates the amount of current supplied to the transformer and so increases or diminishes the output of the machine. In other machines the current supplied to the transformer is regulated by means of a variable resistance that is in- cluded in series with the primary coil ; while in some machines the high-frequency current to the patient is regulated by taking a varying number of turns of the secondary high-frequency coil into circuit. Physiological Action of Diathermy. — The sustained high-frequency currents supplied by the diathermy machine raise the temperature of the tissues which they traverse, and such physiological effects that have been observed to follow applications of diathermy are the result of this rise of temperature. The subject has not yet received much experimental investigation. Rechou made some observations on the respiratory exchange of i84 ESSENTIALS OF MEDICAL ELECTRICITY a subject during the application of diathermy (quoted by Bergonie, Archiv. d' Elect. Med., loth March 1913). He found that the first effect of the diathermy was to increase the intake of oxygen and output of carbon dioxide. As the diathermy continued it was foimd that the subject took in less oxygen and gave out less carbon dioxide. The first effect of the diathermy was to increase metabohsm, evidently that concerned in the production of heat ; the second effect was to diminish it, the artificial introduction of a large quantity of heat rendering unnecessary the production of the customary amount of heat by the body. The application of general diathermy to the normal subject by means of electrodes grasped by the hands or embracing the forearms is followed by a sensation of heat. The heat is felt first in the narrowest part of the forearm ; it then spreads up the arms ; afterwards the whole body feels warmer, but the greatest heat is always felt in the lower part of the forearm, where the path for the current is narrowest and the resistance therefore greatest. The subject sweats profusely after the dia- thermy has been in progress for some minutes, more especially from the upper limbs and face, when the electrodes are applied to the forearms or hands. The frequency of the pulse rises and, in some subjects, the blood pressure falls. Occasionally the fall is accom- panied by a feeling of faintness and the diatherrriy must then be stopped. Proof oi the Heating of the Deep Parts. — ^Experiments on animals have been carried out by various workers, and they show that the heat produced by the diathermy penetrates into the deep parts and is not confined to the skin. Thus the hind limbs of animals have been coagu- lated in their entirety. Electrodes have been placed on the exterior of an animal's skull and the diathermy APPLICATION OF DIATHERMY TO BODY 185 current passed through the brain. A thermometer with its bulb in the lateral ventricle showed, in one experiment, a rise of 1° centigrade after ten minutes' diathermy. In the human subject investigation of the subject is more difficult. The author was able to show, in one case, a rise of temperature of i'2° F. in the posterior fornix vaginae after appUcation of diathermy to the pelvic region by way of electrodes placed over the hypogastrium and under the gluteal region. How Diathermy is applied to the Body.— Diathermy may be apphed so as to raise the temperature of the whole body (general diathermy), or of part of it (local dia thermy). The passage of the diathermy current through any part heats not only the fixed tissues, but also the blood that circulates through them, so that if the applica- tion of the current is for long, and particularly if a large part of the body is traversed by the current, the tempera- ture of the rest of the body will be raised by means of the heated blood. Therefore the local treatment becomes, to a greater or lesser degree, a general treatment as well. (a) General Treatment. — ^This may be given on a special form of condenser couch. It was designed by Schittenhehn, and is shown in Fig. 53. The patient Ues on sheet ebonite one-eighth of an inch thick, placed on the framework of the couch. Under it lies a large metal sheet divided into four separate parts. One Hes under each lower extremity and one under each shoulder and corresponding side of the trunk. The cables from the diathermy machine are connected to two terminals at the head of the couch. A ** changing box " is fixed to the head of the couch. In it are enclosed five cranks, and each of the four parts of the metal sheet is connected to one of these. By turning these cranks into the appro- priate positions it is possible to connect either cable from the diathermy machine with any division or divisions of i86 ESSENTIALS OF MEDICAL ELECTRICITY the metal plate. Suppose that one cable is connected to the division under the right shoulder, the other to the mm ff F"l IB — ^fi \^ 11 to l] 1= 6 II Ph division under the right lower limb. Each division will then become alternately positively and negatively LOCAL DIATHERMY TREATMENT 187 charged, the frequency of the alternation of the charge corresponding to the frequency of the oscillation of the diathermy current. Charges will be induced on the parts of the body in contact with the ebonite sheet over the metal plates. These induced charges will change their sign synchronously with the inducing charges. Conse- quently induced currents will oscillate through the body between the right shoulder and the right lower limb. By suitable arrangement of the cranks in the changing box the currents may be made to oscillate between shoulder and shoulder, or between both shoulders and both lower limbs, or in any other direction. When applying diathermy on the condenser couch the patient need not remove clothes, but metal, such as coins or keys in the pockets, and watch and chain, are best removed, also corsets, if they contain metal. He gradually experiences the sensation of warmth, and it is first felt in the parts in contact with the couch. A watch should be kept on the pulse and blood pressure, for occasionally the latter falls and the patient feels faint. The treatment must then be stopped, {b) Local Treatment.' — The part to be treated is enclosed between two electrodes placed on opposite sides. In the case of limbs, they may be placed above and below. The electrodes are made of metal plate, and are of different sizes and shapes, oblong, square or circular. They should roughly approximate in size and shape to the part to which they are applied. The metal plates may be placed in direct contact with the slightly damped skin, or an absorbent pad about one-fourth of an inch in thickness, soaked in salt solution, may be inter- posed. With the latter device a better contact may be ensured when the surface is irregular. Tap-water must not be used to soak the pads with, as it does not contain sufficient saline substances in solution (ions) to conduct the current readily. If used, the electrodes become i88 ESSENTIALS OF MEDICAL ELECTRICITY gradually hotter and may cause burns. The strength of the salt solution should not be less than io%. When the electrodes are securely bandaged in position the current is turned on and gradually increased till the patient begins to perceive warmth. The warmth gradu- ally increases and the current may be afterwards further increased till the heat is as much as can be borne without discomfort. The patient's sensation is a sufficient guide to ensure diathermy without burns, but if there is anaesthesia, diathermy cannot be applied without some risk. Nagelschmidt has composed a table showing the maximum current that can be safely borne by the skin with different size electrodes. The latter must make the best possible contact with the skin and the current should not be applied at once in the maximum permissible strength. Local treatment may also be given on the condenser couch. A terminal on the changing box is connected to an electrode that is placed on the part requiring local treatment. By means of one of the cranks in the chang- ing box this is brought into connection with one of the cables of the diathermy machine. The other cable is brought into connection with one or more of the metal plates under the ebonite sheet. By this method the part requiring local treatment will be very effectively heated, while, at the same time, the other parts will receive a less intense but more general treatment. This method is particularly suitable when a large portion of the body, such as the chest or abdomen, is to be subjected to diathermy. In the absence of a condenser couch, general treatment may be given by applying two electrodes, one to each forearm. The current therefore passes along the arms, across and between the shoulders. In this way the temperature of the arms is raised, while the heated blood passes to the rest of the body and gradually raises its MEDICAL DIATHERMY 189 temperature. Electrodes may then be applied to the legs, so that the current passes along them and across the pelvis, producing local and general heating as before. The current may be directed simultaneously from arm to arm and from leg to leg, by attaching electrodes to each part and using double or bifurcated cables. Special electrodes are made for diathermy of special parts. Metal tubes with closed, rounded ends are used for insertion into rectum or vagina. Vacuum electrodes, the same as used for high frequency, may also be used for local application, so as to combine the action of the diathermy with that of the ozone and oxides of nitrogen. These electrodes are described in the preceding chapter. Medical Diathermy. — The appUcation of diathermy to medical cases has not been practised long enough in this country to allow a definite statement of the morbid con- ditions for which it is to be applied. Maladies and morbid conditions that are likely to benefit from applica- tion of heat, are likely to improve further by diathermy. Heat as ordinarily applied waxms the skin only. The sustained high-frequency current heats the deep parts as well as the superficial, whereas other methods produce only surface-heating or "epithermy." Inflammation of nerves, joints and serous membranes, accompanied by pain, are often reUeved by diathermy. Diathermy seems to be very successful for cases of gonorrhoeal arthritis. The gonococcus is apparently sensitive to small rises of temperature. By the diathermy current the joint is heated through. The temperature of the whole body can be raised by general diathermy, and brought into a state of " physio- logical fever." The condition of lowered vitality, in which there is depression of the functional activity of the organs — cases to which the name "misere physio- logique " has been appHed — ^are much benefited by general I90 ESSENTIALS OF MEDICAL ELECTRICITY diathermy, which suppHes the heat that the body can- not supply, in its state of impoverished vitahty. Nagel- schmidt claims that diathermy can lower abnormally high blood pressures. He applies one electrode to the precordium and another to the back. Angina pectoris is said by the same writer to benefit by similar treatment. Surgical Diathermy. — ^By means of the diathermy current it is possible to raise the temperature of the tissues sufficiently high to destroy their vitahty. They can be coagulated in situ. The diathermy current can therefore be used to destroy new growths, both innocent and malignant. The coagulation is due to the heat that is produced within the tissues as the current traverses them. Such instruments as the galvano- thermo-cautery and the Paquelin cautery simply char the tissues locally, and, as the latter conduct heat very badly, there is very httle spread of coagulation beyond the carbonised cavity. The tissues conduct electricity well, and, as it is the electricity that develops the heat, there is not this limitation to the spread of the coagula- tion. It is therefore easy, by means of the diathermy current, to coagulate a malignant growth in its entirety " through and through." The rise of temperature necessary to coagulate a growth is brought about by reducing the size of the electrode in contact with the growth (the active electrode) to that of a needle or small disc or button. The other electrode (the indifferent electrode) covers a large area of skin. The current density will be greatest at the point where the current leaves the electrode to enter the tissues, and there the temperature will reach the highest. As the distance below the surface increases, so the current density lessens and the temperature diminishes. For a certain distance below the electrode the tissue is coagulated. ELECTRODES FOR SURGICAL DIATHERMY 191 The depth to which coagulation spreads depends, apart from the time during which the current flows, upon the shape and size of the active electrode and the vascu- larity of the tissue. The larger the surface of contact between the active electrode and the tissue, the greater will be the depth to which coagulation will extend. If a small surface electrode is used the current density is great at the point of contact with the skin, and the temperature there very quickly rises to a point at which the tissue is dried. Dried tissue conducts the current badly and sparks make their appearance and the current has to be switched off soon after it is started, so that there is no time for the coagulation to spread far. The depth to which coagulation spreads depends also on the vascularity of the tissue. The circulating blood tends to dissipate the heat and may prevent coagulation in the region where the temperature would be, in less vascular tissue, just sufficient to cause it. As an approximate guide, it may be taken that the coagulation will spread below the electrode for a distance equal to the diameter of the latter. Electrodes. — The most generally used active electrode consists of a short rod-shaped ebonite handle with a metal core. Into the proximal end of this is screwed one of the cables leading to the diathermy machine. To the distal end is attached a metal end-piece. The latter is usually a disc or button, bearing sometimes one or more short metal spikes. Special end-pieces have been designed for less accessible regions, such as the larynx and oesophagus. The indifferent electrode is composed of a pad of lint or folded towel measuring 12 inches by 8 inches. It is soaked in strong salt solution and placed on the chest or abdomen. On it is placed a piece of sheet lead one sixteenth of an inch thick and 8 inches long and 6 inches broad, and to it is connected one of the cables from the diathermy machine. 192 ESSENTIALS OF MEDICAL ELECTRICITY How Surgical Diathermy is performed. — ^An anaesthetic is required except when very small portions of tissue have to be destroyed and the applications are momen- tary. A general anaesthetic is required if the tissue to be destroyed Ues in a less accessible region, such as the mouth and throat, and if a large mass of tissue has to be destroyed. A local anaesthetic may be used in some cases. The electrodes axe placed in position, the in- different electrode on the chest or abdomen, the active electrode on the growth. The current is then switched on and gradually increased. Bubbles of gas are seen escaping from the region of the active electrode and the tissue under the latter whitens from coagulation. The current is then switched off and the electrode placed on an adjoining part. The current need not be further adjusted, but it is merely switched on till coagulation has again taken place. In this way the whole of the growth is coagulated. If the growth is fungating it may be necessary to gently scrape off the coagulated tissue and coagulate further till it is thought that healthy tissue has been reached. Advantages of Diathermic Coagulation or Cautery. — The operation is quick and patients do not suffer from shock after it. They are able to get up after forty-eight hours in most cases and leave hospital in a few days. The blood vessels and lymphatics are sealed by the coagulation of their contents. Oedema of the surround- ing parts comes on during or soon after the operation and a copious discharge of lymph sets in and lasts some hours. The coagulated tissue sloughs away and the cavity quickly fills with granulation tissue. A point of special interest is the absence of adhesions at subsequent periods. Results. — ^Diathermy has been used of late for the treatment of inoperable malignant growths. Many of RESULTS OF SURGICAL DIATHERMY 193 these have been made to disappear, and although re- currence takes place, this event has in many cases been postponed for a year or even longer. One patient with an inoperable growth of the tonsil and fauces lived as long as two years and nine months after the first application of diathermy. It is always necessary to keep the cases under observation and reapply the diathermy when recurrence is noticed. The patient referred to had six appUcations. Other cases show recurrence at an earher date, but considerable improvement is the rule, and the relief from distressing symptoms, such as pain, discharge and constant expectoration when the growth has involved the mouth and throat, is a common occurrence. Diathermy would give its best results in the treatment of operable growths. There is no reason why removal with the knife should not follow diathermy, as the destruction of the main mass of the growth and the seal- ing of the blood vessels and lymphatics would minimise chances of dissemination. Diathermy has also been tried for non-mahgnant growths. It has given good results in cases of large naevi. Naevi of the mucous membranes are more suitable than naevi of the skin. For papillomata of the bladder it would seem the treatment far excellence. Each papilloma is in turn brought into view by the cystoscope and an insulated wire is passed along the channel in- tended for the catheter to the ureter. It makes contact with the papilloma and the current quickly coagulates it.i * For a more complete account of diathermy see Archives of the Roentgen Ray, July, 19 14, et seq. CHAPTER XIII THE USE OF STATIC ELECTRICITY Apparatus required. — ^The first requirement is a gener- ator of static electricity, or, as it is called, a " static machine." The old frictional generator has been long discarded and its place has been taken by the so-called "influence machines." There are two principal kinds, the Holtz machine and its modifications and the Wimshurst machine. The Holtz machine is very popular in America, but it possesses at least two distinct disadvantages. It has first to be given an initial charge from a smaU Wims- hurst before it wiU start generating, and it is also sensitive to the changes of the weather. The Wimshurst Machine is self-exciting and has no tendency to reverse during action, and on this account is most popular in this country. With some machines of this type one can never be sure beforehand which pole will be positive and which one negative, but once started the polarity will not change during the continuance of the run. It is not so sensitive to changes of the weather. In very damp weather, if it is not enclosed in an air-tight case, its output will be reduced and it will not be self- exciting. Fig. 54 shows a small Wimshurst. It consists in its simplest form of two circular glass plates, each mounted on the end of a hollow boss of wood upon which a groove is turned to act as a pulley for driving the plate. The wooden bosses with the plates are mounted in a horizontal steel shaft, so that the plates are 194 WIMSHURST MACHINE 195 facing each other and about one-eighth of an inch apart. Directly below the plates is another horizontal shaft, upon which are secured two large wooden pulleys exactly oppccite the grooves turned on the wooden bosses. A handle is provided at one end of the lower shaft, and two leather belts, one of which is crossed, are fitted round each pulley and its corresponding boss. When the handle is turned the plates will revolve in opposite directions. The plates are well varnished, and attached to their outer surfaces are a number of radial sectors of tin-foil or thin brass. These are equally spaced all round the discs — ^they make the machine more easily self-exciting, but are not essential to its action, especially in the case of larger machines. By means of a neutral- ising rod tipped with a fine wire or tinsel brush at each end, mounted so as to be adjustable con- centrically with the shaft upon which the plates revolve, each pair of sectors at opposite ends of a diameter are placed momentarily in metallic contact twice during each revolution. These neutralising rods must be adjusted to the point of maxi- mum efficiency, which will be readily found by experiment . If we stand facing the plate, and its direction of rotation be clockwise, the neutralising rod will be in the position of the hands of the clock indicating five minutes to five. This will vary in different machines, but the correct position will be found very near this point. The fixed conductors are moimted at the ends of the horizontal Fig. 54. — Wimshurst Machine 196 ESSENTIALS OF MEDICAL ELECTRICITY diameter and consist of two forks, with collecting points on the inside pointing towards each other, and the plates revolving between. These forks are mounted on ebonite or glass pillars, and to each fork is attached an electrode consisting of a metal rod bearing a brass ball at one end and an ebonite handle at the other. The electrodes are movable, and an operator can grasp the insulating handles and move the electrodes, so that the brass balls can be brought closer together or farther apart. The collecting device with the discharging apparatus is some- times called the " prime conductor." When the plates are revolved, positive electricity collects on one electrode, negative on the other. If the electrodes are sufficiently close together a succession of fine crackling sparks passes across the intervening gap. With a large machine the sparks may be many inches long. The difference of potential between the charges on the two electrodes reaches a very high value. As usually supphed, the machines have a Leyden jar attached to each electrode, the latter being connected to the inner coating of the jar. When their outer coatings are connected together and the machine set in action the character of the discharge is completely altered. Instead of the soft crackling brush, the discharge takes place at definite intervals and each is accompanied by a more or less loud report. The Leyden jar greatly increases the capacity of the electrodes, so that they can take much larger charges, but a longer time elapses before these larger charges reach a potential sufficiently high to overcome the resistance of the air between them. A loud, intensely white, thick spark accompanies the discharge. A shock from a large machine with the jars connected might be fatal. The jars are, in most cases, to be dis- connected before any static machine is used for treating patients. WIMSHURST MACHINE 197 There are made by some manufacturers various modifications of the Wimshurst. One has ebonite plates, and, on account of the toughness and flexibihty of the material, the plates can be driven at a very high speed. Another has plates made of compressed mica, which can also be driven at a high speed. The advan- tage of high speed is that the same difference of potential can be obtained with a smaller plate, making the machine less bulky. The disadvantages of ebonite are that it often becomes bent and buckled out of shape. Also its insulating properties become very much impaired after a time, and the output of the machine correspondingly reduced. For medical purposes the Wimshurst machine should have not less than eight plates, thirty or thirty-six inches in diameter. The machine should be enclosed in an air-tight case with glass windows, so as to prevent the attraction of particles of soot and dust from the atmosphere. The air inside the case can be dried by desiccators, such as boxes of quicklime or trays of sulphuric acid. The machine is driven by a small electric motor, or a gas or oil engine. Glass coated with shellac is at present the most suit- able material for the plates. Ebonite is lighter, and plates made of this material can be driven at a higher speed than glass, so that electricity can be generated at a quicker rate. But ebonite deteriorates after a time, as chemical changes take place on its surface and impair its insulating properties. It loses its black colour and acquires a greenish tint. Further, it tends to warp, so that the plates come in contact as they revolve. The Wimshurst machine has the following advantages. As soon as the plates begin to revolve it begins to gener- ate electricity. The other machines will not generate electricity when the plates are made to revolve, unless an initial charge has been given to it first. The Wimshurst machine is less sensitive to damp than the others. 198 ESSENTIALS OF MEDICAL ELECTRICITY The Holtz Machine. — In its simplest form this machine (Fig- 55) consists of two vertical glass plates, one of which (A) is fixed, while the other {B) can revolve parallel to it. The plates are close together, but do not touch. The fixed plate is shghtly larger than the revolving plate. In the fixed plate are cut two "windows " {a and b) diametric- FiG. 55. — Holtz Machine (from Electrical hifluence Machines^ by J. Gray) ally opposite each other. Two pieces of paper, known as " field plates," are fastened on to the fixed glass plate, one {d) being placed above the window (&), the other being placed below the window [a). A strip of paper attached to each of these field plates projects through the window on the same side and points at the revolving plate with- out touching it. The latter plate revolves in a direction opposite to that in which the strips point. Two metal rods {g and i), bearing metal spikes, collect the electric MODIFICATIONS OF HOLTZ MACHINE 199 charges from the revolving plate on to the metal balls shown in the figure. Two of these balls, mounted on the ends of brass rods with insulating handles, are movable, and can be brought closer together or farther apart. They are made to touch when the machine is to be started. The rod tv, known as the " neutralising rod," carries a comb at each end, the points of which are directed towards the front of the revolving plate. To start the machine, an electric charge from a rubbed ebonite rod is given to one of the field plates. The movable plate is then revolved and the balls drawn apart. Sparks then dart across the gap separating them. The modern form has six or eight plates, arranged in pairs, each pair consisting of one fixed and one revolving plate. It is enclosed in an air-tight case and is driven by a motor like the Wimshurst machine. An initial charge of electricity must be administered to one of the field plates of the Holtz machine before the plates are made to revolve, otherwise no electricity will be generated. A very small Wimshurst machine is usually placed in the case to generate this initial charge. The Toepler machine (known also as the Voss machine) works on the same principle as the Holtz ; it is usually self-starting, requiring no initial charge. The Baker paper-disc machine is much used in America, and those who have used it in this country speak favourably of it. It is a modified Toepler machine. The stationary plates, four in number, are made of glass. The four revolving plates are made of paper. Each plate is composed of twenty-four discs of paper saturated in shellac and other gums, compressed together between hot metal discs. These plates are light, unbreakable and do not readily condense moisture on their surfaces, and so their insulating properties are not impaired. They can be rotated 2000 times per minute. The usual rate with glass plates is 350 per minute. The machine is enclosed 200 ESSENTIALS OF MEDICAL ELECTRICITY in a case and driven by a motor. It requires an initial charge before it generates further quantities. A small Wimshurst machine is provided for the purpose. Out- side the case enclosing the static machine are the two prime conductors. The latter are fitted with sliding rods bearing a brass ball at one end and an ebonite handle at the other. The air space between the brass balls is the spark gap and its length can be regulated by the sliding rods. Static machines are usually provided with a pair of Leyden jars. One is connected with each prime con- ductor. In most methods of applying static electricity to patients they are not used and should be disconnected. Accessory Apparatus. — The accessory apparatus in- cludes an insulating platform, a set of electrodes, lengths of brass chain for connecting the electrodes to the prime conductors or to other parts where necessary, and a long brass rod bent to a hook at one end, like a shepherd's crook, for the purpose of connecting the patient to the machine. The insulating platform supports the patient. It is mounted on four stout glass legs. The legs should be coated with shellac to prevent the condensation of moisture on them, which would impair their insulating power. They should be at least ten inches long. When powerful machines are used, the platform should be raised thirteen inches off the ground by its insulating legs. The wooden framework should have all corners and edges rounded off. The platform should be large and strong enough to support the heaviest patient. It should measure 5 feet by 2 feet 4 inches. The patient sits on a chair on the platform. The chair should contain no metal, and all edges should be rounded off. The patient must sometimes be in a reclining position. When this is necessary, the chair should be replaced by a wicker couch. ELECTRODES FOR STATIC MACHINE 201 Four common types of electrode are shown in Fig. 56. Each consists of an ebonite handle with a metal end- piece. The latter may be a metal rod, tapering to a point, or it may terminate in a metal disc bearing a number of metal spikes. These are known as the single-point and multiple-point electrode respectively. The metal may terminate in a brass ball (ball-electrode) or may carry a metal roller (roller electrode) . The metal portion of each 1 Fig. 56. — Electrodes for use with Static Machine 1. Single-point (metal) electrode 2. Multiple-point (metal) electrode 3. Metal ball electrode 4. Roller electrode electrode bears a small metal ring, to which may be attached the brass chain connecting it to the machine. These electrodes have been modified in various ways. Thus, the handle may be made of some partially con- ducting material, such as wood that can absorb a certain amount of moisture. It may terminate in a metal or wooden point. The chain that connects this electrode with the static machine is attached, not to the metal end, but to a short length of metal tube that slides over the 202 ESSENTIALS OF MEDICAL ELECTRICITY handle, and its position can be adjusted so as to include a greater or smaller length of wood between it and the tip of the electrode. This electrode has been used especially for the application of the static breeze (see below). The Machine in Action. — When the motor is started and the plates are revolving, positive electricity collects on one prime conductor, negative on the other, and when the sUding rods are brought towards each other sparks pass between them with a frequency that increases the closer the rods approach one another. It is necessary to know the prime conductor on which the positive and on which the negative electricity accumu- lates, because each time the machine is started the same prime conductor does not invariably charge up the same. A convenient way to "test the polarity," as it is called, is to proceed as follows. Start the machine and bring the single metal point electrode gradually nearer to one or other of the prime conductors. The point electrode should be connected to earth by a chain attached to the ring on the metal part of the electrode, and at the other end to a water or gas pipe, or the floor of the room if of wood or stone. Gradually bring the point of the electrode nearer and nearer, and, as it approaches the positive prime conductor a star of light will appear on the point, even at a distance of several inches, and this star of light will remain without much alteration until the point is brought up almost in contact with the knob ; then small sparks pass. If approached to the negative prime conductor in the same way, the discharge takes the form of a visible brush of non-luminous noiseless sparks when the point is still at a distance of two or three inches from the knob. It is easy to recognise these differences in the discharge to the point, and from them to know which prime conductor is positive and which is negative. STATIC BATH 203 Static electricity means, literally, electricity " at rest." It is, however, only at rest when it is on the prime conductor and not leaking off. When it is applied to the body it flows on to and off from the latter. The body is alternately charged and discharged in some of the applications, so that static electricity becomes " current electricity." The current, however, is extremely small, not greater than a fraction of a milliampere, although its voltage is exceedingly high, reaching half-a-million or more. The Methods of Applying Static Electricity to the Patient. — ^The Static Bath. — In this method of applica- tion the patient is merely charged with electricity. He sits on a chair on the insulated platform. The chair should contain no metal. The patient is connected to the positive prime conductor of the machine by means of the metal rod with the crook at the end. The end is hooked over the sliding rod of the positive conductor, while the other end is placed on the floor of the insulated platform, not in contact with the patient or the chair. The patient and the insulating stool should be at least two feet away from the machine or from the walls and other objects. Before connecting the platform with the machine, the latter should be set in action and the polarity tested. The sliding rods are then placed in contact, and the platform is connected to the positive prime con- ductor. The sliding rods are then drawn as far apart as possible. The patient is charged positively, and when the voltage of this charge reaches a sufficient height the electricity leaks off from the surface of the body. The sensation is agreeable, and the skin feels as if it were in contact with cobwebs. For a stronger effect, or if the machine is not powerful, the end of the crook should be placed on a sheet of metal on the platform and two of the legs of the chair should rest on it. For a still stronger 204 ESSENTIALS OF MEDICAL ELECTRICITY effect, the feet of the patient should rest on the metal plate. When the patient actually holds the metal rod the effect is strongest of all. The latter method of con- 9i 1 i Fig. 57. — Stati„ Breeze nection between prime conductor and patient is to be adopted when powerful machines are not available (Fig. 57)- Treatment may be continued for fifteen minutes or STATIC WAVE CURRENT 205 longer. It is the mildest form of static electrical treat- ment and it produces no unpleasant sensations. It is indicated for hypersensitive, nervous patients for the production of tonic effects. Its beneficial effects are possibly due to gentle stimula- tion of the sensory nerves of the skin, caused by the con- tinuous leakage of the charge from the surface of the body. Another method of giving the static bath is to charge the patient positively as before, and then bring the negative sliding rod gradually nearer to the positive till a spark passes ; at this moment the patient is dis- charged, but is quickly recharged and again discharged, and so on. A stream of sparks passes between the balls on the end of the sliding rods. The rate at which the sparks follow each other depends upon the width of the spark-gap and the rate at which the electricity is gener- ated. The width of the gap should be adjusted so that the sparks pass apparently continuously. The patient should be arranged on the chair on the platform with the feet on the metal plate, the latter connected by the brass rod with the positive prime conductor. If there is a sensation of sparks on the feet the boots should be removed. This modified method is rather more vigorous than that of simple charging. It is known as the method of " potential alternation " or " interrupted electrifica- tion." The sparks cause a continuous noise that is disagreeable to some patients. The Static Wave Current. — ^This is known also as the " Morton wave current." To apply it, the patient sits on a chair on the insulating platform . An electrode made of pliable sheet metal cut to the desired shape is applied to the part requiring treatment and connected to the positive prime conductor of the machine by means of a 2o6 ESSENTIALS OF MEDICAL ELECTRICITY wire. The negative prime conductor is earthed by means of a brass chain connected to a water or gas pipe or radiator, or to a wood en or stone floor. The arrangement is shown diagrammatically in Fig. 58. The machine is started and the negative sHding rod is gradually separated from the positive. Sparks at once bridge the gap. With each spark there is a contraction of the Sjxirk ga|> ark G \:^ other and diverge. When the \_ JL nJ charged body is removed the '^'^ '' ^ induced charges neutralise each other and the leaves fall together again. But if the metal ball is momentarily touched before the charged body is removed the induced charge that is repelled to the gold leaves is now repelled to earth and the leaves, being faU together. If now the Gold Gold leaves positively charged (by induction) Fig. 62. — Electroscope now no longer charged, original charged body is removed, the charge that was induced on the baU now spreads itself over the metal rod and the leaves. The latter diverge once more. Suppose that the original body was positively charged, the leaves would then be negatively charged. If now a second charged body, the nature of the charge being unknown, be brought near the ball without touching, it will induce on to the leaves an extra charge of the same nature as that on itself. If the leaves diverge still further, the extra charge on the leaves is of the same nature as that DENSITY: POTENTIAL 259 pre-existing on it — viz. negative. The unknown charge is therefore negative. But if the leaves approach one another the unknown charge is positive. Density : Potential. — ^An electrical charge resides only on the surface of a conductor. The density of a charge is tha amount of electricity per unit of surface area. If the electricity is not evenly distributed over the surface, the density must vary in different parts. The distribu- tion is even only over the surface of a sphere, and so the density is the same all over. If the surface of a conductor is not even, the distribution of the electricity wiU be uneven ; it wiU be more concentrated on the parts that are more convex, while the greatest concentration will be on edges and points. The density wiU therefore be greatest at edges and points, and here the electricity tends to leak off from the conductor. The term " potential " is frequently used in reference to electrical charges. Conductors are said to be charged to a high potential or to a low potential. The potential of a charge does not refer to the actual quantity of electri- city, but to the quantity in relation to the surface area of the conductor on which it resides. The following comparison may make the meaning of potential clearer. A certain quantity of air pumped into an inexpansible vessel would exert a certain pressure on the walls ; if the capacity of the vessel was reduced to one half, the same quantity of air (measured in the uncompressed state) would exert double the pressure, although the quantity of air would be the same. In the case of the electrical charge, a certain quantity of electricity would charge a conductor to a certain potential. The same quantity of electricity would charge a conductor of half the capacity to double the potential. In the latter case the density of the charge — i.e. the quantity of electricity per unit of area — is doubled and the result is that the 26o ESSENTIALS OF MEDICAL ELECTRICITY electricity is at a higher potential or " pressure " ; the electricity has a greater capacity for doing electrical work and overcoming resistance. Electricity at high potential flows or tends to flow to parts where it exists at lower potential, and if . the diflerence of potential is high it may overcome the resistance of the air — that is, if air separates the two conductors charged to different potentials — and pass across in the form of long sparks. The potential of the earth's surface is taken as zero. All bodies that are connected to earth by conductors (or " earthed ") must be at the same zero potential. Positively charged bodies may be regarded as bodies charged to a potential above zero ; negatively charged bodies as those charged to a potential below zero. Capacity. — The quantity of electricity that a con- ductor is capable of receiving is determined by the " capacity " of the conductor. As the electricity resides only on the surface, the capacity of a conductor depends upon its surface area. For electrical purposes the capacity is measured, not by the surface area, but by the quantity of electricity required to raise its potential from zero to unity. If a unit quantity of electricity is required to raise the potential from zero to unity, the conductor is said to have a unit capacity. The unit of capacity is a " farad." When we say that a conductor has a certain capacity, it is not to be thought that it is capable of holding only a certain fixed charge. The amount of electricity that a conductor will hold depends, apart from its surface area, on the potential of the source of supply ; if this is suffi- ciently high, electricity will pass to the conductor, raising its potential till the electricity begins to leak off. If, on the other hand, the potential of the source of supply is low, electricity will pass to the conductor till the potential of the charge on the latter equals that of the CONDENSERS 261 source of supply, and no more electricity can then pass. To return to the air pressure analogy. A pump capable of delivering air at any pressure will continue to force air into a vessel, raising the pressure within it higher and higher till the air escapes through a valve ; on the other hand, if the pump delivers air at a low pressure, the pressure inside the vessel will soon equal that of the air supplied by the pump, and then no more will pass in. The capacity of a conductor may be greatly increased by bringing close to it a second conductor without actually touching it, the two being separated by some insulating material, such as the air, or glass, ebonite, etc. Such an arrangement of conductors is termed a condenser, because the first conductor is now able to hold a much larger quantity of electricity than it could before the second conductor was in close apposition. Condensers. — ^A condenser consists of two conducting surfaces separated by some insulating material. The latter is sometimes called the " dielectric." The capacity of a condenser depends on : (a) the area of the conduct- ing surfaces — ^the greater the surface the greater the capacity ; (h) the thinness of the dielectric — ^the thinner the dielectric the greater the capacity ; (c) the material of the dielectric — glass gives a condenser a greater capacity than the same thickness of air. The simplest form of condenser consists of two metal sheets of equal size, facing each other, with a layer of insulating material of larger area interposed, allowing them to come into close apposition without actual contact. The most familiar form of condenser is the well-known Leyden jar (Fig. 63), which in its most common form con- sists of a glass bottle which is partially coated inside and out with tin-foil, and provided with a stopper of some insulating material through which passes a stout wire. 262 ESSENTIALS OF MEDICAL ELECTRICITY On the outer end of this is mounted a metallic knob, and from the inner end hangs a length of brass chain sufficient to make good contact with the inner coating. Here the two tin-foil surfaces are the conductors — sometimes called the " armatures " — and the glass the dielectric. To charge a condenser one of the conducting surfaces is connected to a source of electricity, and the other surface is connected to earth. In the case of the Leyden jar, the metallic knob is connected to the source of the electricity, while the outer coat is brought into contact with earth by standing the jar on a table, or by holding the jar in the hand, grasping the outer coating. The inner coating is charged — by conduction — from the source of supply, while the outer coating is charged by induction, the induced charge of the same sign being repelled to earth, that of the opposite sign remaining on the outer coat, attracted by the charge on the inner coat. Suppose that the potential of the source Fig. 63.— of supply is +i. The inner coat of the jar ey en Jar ^-j^^j^ connected to this source is thereby charged to the same potential. But a larger quantity of electricity is required to charge it to this potential than would be required if the inner coating stood by itself. Suppose the potential of the induced charge on the outer coat is -J. The potential of the inner coat is now i-| or +J. The inner coat is thus brought to a lower potential than that of the supply, and, therefore, more electricity must pass to the inner coat until the potentials are equal. To discharge the jar a bent wire is placed with one end against the outer coating, and while retaining it there, the other end is brought gradually closer to the knob. Presently a spark passes and the jar is said to be discharged. PRODUCTION OF STATIC ELECTRICITY 263 As a matter of fact it is not completely discharged unless the wire has been brought in contact with the knob and the outer coating at the same instant, for if we try- again to discharge the jar another spark wiU pass, though much smaller and shorter than the first. This is due to the " residual " charge, as it is caUed. It may be as well to mention here that when We discharge a jar the spark is not single — passing once only from wire to knob, or vice versa ; what appears to be a single spark is reaUy a series of sparks passing alternately in opposite directions at an enormously rapid rate. The oscillation may, under suitable circimistances, reach a frequency of thousands or even millions per second. The discharge of a condenser is therefore a current of high-frequency oscillation or alternation, providing certain requirements in the circuit along which the discharge takes place are fulfilled. These have been mentioned in the chapter on high frequency. The oscillatory discharges of condensers are used for electro-medical treatment, and their application forms an important branch of modem electro-therapy — ^viz. high frequency and diathermy. Condenser discharges have been recently introduced for the purpose of muscle- testing and treatment of paralysis and other conditions. The Production of Static Electricity for Medical Purposes. — Static electric machines are used to generate a continuous supply of static electricity, and are of two kinds, frictional and inductive. The old-fashioned revolving glass cylinder, with an amalgamated leather rubber and brass collector or prime conductor, is an example of the frictional typ^- This type of machine is never used for medical purposes, and is now seen only in physical laboratories. Induction or influence static machines are much more reliable, but how they work is not easy to describe or understand. 264 ESSENTIALS OF MEDICAL ELECTRICITY The principle may be outlined as follows : — A body, A, is charged positively and brought near another body, B. B is therefore charged by induction, as described under " Induction." B is momentarily connected to earth, whereupon the positive induced charge escapes, and the negative induced charge remains. B and A are now separated from one another. The induced negative charge on B is collected and stored on another fixed conductor, while the original positive charge on A can be used over and over again to induce fresh charges. The mechanical energy expended in separating the oppositely charged bodies, A and B, is converted into electrical energy. Two types of influence machine have been described in Chapter XIII. (B) Current Electricity If two conductors at different potentials are con- nected by a wire, the difference of potential will be equalised and a current of electricity, of momentary duration, will pass along the wire. If the conductor at the higher potential can be continuously suppHed with electricity, a continuous current will flow along the wire. Continuous currents of electricity can be obtained by chemical, thermal or mechanical methods. The currents that are supplied by the different types of cell are obtained by chemical methods. Batteries of these cells form an important source of electrical supply for medical purposes, and the principles on which they work wiU be considered first. Production of Electrical Currents by Chemical Methods. — If two dissimilar metals are brought into contact a slight difference of potential is set up between them, that of one being raised (positive), that of the other being lowered (negative). The degree of difference is always PRODUCTION OF CURRENTS 265 very slight, and it varies according to the metals taken, and it does not depend upon the amount of metal or the extent of surface in contact. Here again it is possible to draw up a Hst of substances — ^metals or conductors in this case — each of which will be positively electrified when brought into contact with any metal succeeding it, and negatively electrified with any metal coming before it in the list : 4- Sodium Copper Zinc . Silver Lead Platimmi Tin —Carbon Carbon is not a metal, but is included in this Ust on account of its good conducting properties, and from the fact that it is now used so much in all branches of electrical work. If zinc and copper be brought together, zinc is positive and copper is negative, while if copper and carbon be brought together, the copper is positive and the carbon negative. The more one metal is removed from another in the hst, the greater is the difference of potential. It will be noticed that those metals nearest the + end of the list are the most oxidisable, while the reverse holds good for metals at the - end. It is impossible, however, to obtain an electrical current by simply bringing dissimilar metals into con- tact. If the circuit is completed by connecting together the free ends of the two metals in contact, either directly or by means of a third metal, new contacts of dissimilar metals are made and the difference of potential first set up would be effaced. Apart from this, the production of a continuous current of electricity, by simply bringing dissimilar metals into contact, would be impossible, according to the principle of the conservation of energy, seeing that the metals are not altered or used up. If, 266 ESSENTIALS OF MEDICAL ELECTRICITY however, the two metals in contact are immersed in some fluid that is capable of acting chemically on one of them or acting more vigorously on one than on the other, a continuous current can be produced while the chemical action proceeds. Thus if a piece of copper and a piece of zinc are fixed together, end to end, the copper becomes negatively charged, the zinc positively charged. If the joined metals are immersed in dilute sulphuric acid, a circuit is now completed and an electrical current flows from the zinc, through the acid, to the copper, and through the copper into the zinc. Simultaneously, the zinc is slowly dissolved by the acid. If the joined metals are bent so that only the free ends are immersed in the acid, the junction being outside, an electrical current will flow as before and in the same direction. Such an arrangement is known as a " simple voltaic cell." It serves to illustrate the chemical changes that occur during the production of an electrical current and to explain the meaning of some commonly used terms. Voltaic Cell. — ^A simple voltaic cell may be constructed by filling a beaker with io% sulphuric acid, partially immersing it in two strips of metal, one of zinc, the other of copper. These strips are placed parallel to each other and with one end of each above the surface of the acid. If the strips do not touch one another, above or below the surface of the acid, the following changes occur. The zinc gradually dissolves in the acid, and zinc sulphate and hydrogen are formed. The former dissolves, while the latter escapes in the form of bubbles. These are seen to form and to escape at the surface of the zinc. If, however, the zinc is pure it is not dissolved by the acid and it undergoes no chemical change till it makes con- tact with the copper. If the contact is made outside the acid, either directly or by means of a wire, the zinc begins VOLTAIC CELL 267 to dissolve and the same chemical change takes place. The hydrogen bubbles, however, make their appearance on the copper, not on the zinc. Some escape from the copper to the surface of the acid, but most of them adhere to the metal and soon cover it completely. While the zinc is dissolving a current of electricity con- tinuously passes around the circuit composed of the metal strips, their connecting wire and the dilute acid. PdsimePLATE yvELOfJiicnmTE IkeAWEPUfTE ^ Fig. 64. — Plates and Poles of a Voltaic Cell The current starts in the cell where the zinc is in contact with the acid. It passes through the acid to the copper plate. It then passes up the copper plate, and then across to the zinc plate, outside the acid, along the con- necting wire. By passing down the zinc to the acid again, the passage along the circuit is completed. The direction of the current of electricity is indicated by the arrows in Fig. 64. If impure zinc is used chemical changes similar to those described would have occurred, and the current would have passed in the same direction. In addition, however, small " parasitic " currents would also have 268 ESSENTIALS OF MEDICAL ELECTRICITY been produced. Commercial zinc contains small quantities of other metals. There are, therefore, dis- similar metals in contact, and when they are immersed in sulphuric acid currents are formed in the way mentioned in the preceding paragraph. Certain names are given to the various parts of a voltaic cell, and as they are continually used it is neces- sary to be quite clear regarding their meaning. In any cell there is an external circuit and an internal circuit, a positive plate and pole, and a negative plate and pole. It is important to distinguish between plate and pole. In Fig. 64 that part of the circuit within the fluid of the cell is called the internal circuit, while that outside is the external circuit. In any circuit or part of a circuit, that part from which the current is coming is positive to a part to which current is flowing. Bearing this in mind, it will be seen that that portion of the zinc which is below the level of the fluid is positive to that part of the copper which is also below the level of the fluid. In the external circuit we see that the part of the copper outside the Uquid is positive to the corre- sponding part of the zinc. These dry portions of the plates are called the poles. If we attach a wire to each of these, the free extremities of these wires become the poles. Thus it will be seen that the wet portion of the zinc is the positive plate and the dry portion is the negative pole, while the wet portion of the copper is the negative plate, the dry portion is the positive pole. This may seem very confusing, but it is not reaUy so, and if the student will take the trouble to get the idea thoroughly there is little chance of his being confused by any of the various arrangements of circuits he will meet with in future. It is customary when referring to the plates of a battery to speak of the poles and not of the plates. The POLARISATION 269 zinc is thus the negative pole and the other element, be it carbon, copper, or platinum, is the positive pole. The electrical current that flows around the circuits of a voltaic cell soon diminishes in strength. It becomes feebler and feebler and finally ceases altogether. The explanation of this is that by the accumulation of minute bubbles on the copper plate the latter is practic- ally transformed into a hydrogen plate, which is electro- positive to zinc, and tends to set up a current in the reverse direction. Also, the film of gas forms a layer of high resistance to the flow of the original current. A cell in this condition is said to be " polarised." The prevention of polarisation is one of the most important objects in the design of a useful cell. The great variety of cells that have been devised have their origin in the various methods that have been adopted to overcome this tendency, and thus give as nearly as possible a constant current during their period of activity. A simple cell like that described is useful for the purpose of demonstration, but is of no value for medical purposes, because the current so quickly diminishes on account of polarisation, and soon falls to zero. Polarisa- tion can be prevented in various ways. One way is to add an oxidising agent, such as potassium bichromate, to the acid solution. The hydrogen is oxidised as soon as it is formed. This method is used in the Poggendorff cell. In this ceU, known also as the " bichromate " cell, carbon is used instead of copper. In the Leclanche cell zinc and carbon are used. The zinc is immersed in a solution of salammoniac (ammonium chloride) contained in a glass jar. The carbon plate is placed inside a porous pot and packed tight round it are fragments of manganese dioxide and powdered carbon. The porous pot thus filled is placed in the jar containing the salammoniac solution. When the zinc and the carbon are connected by a wire, a current passes from the carbon to the zinc 270 ESSENTIALS OF MEDICAL ELECTRICITY outside the cell, and from the zinc to the carbon inside the cell. Fluid is unable to pass through the wall of the porous pot, but the electric current readily traverses it. The zinc dissolves in the salammoniac solution, forming a double chloride of zinc and ammonium, and ammonia gas and hydrogen are liberated. The ammonia dissolves and the hydrogen is oxidised by the manganese dioxide, so that polarisation is prevented. The oxidation is slow, so that if the cell is made to give a current continuously for several minutes polarisation begins and the current begins to diminish in strength. If the cell is allowed to rest, the free hydrogen will be oxidised, and the cell will then provide a current of undiminished strength. Dry Cells. — ^These have almost entirely supplanted other cells for medical purposes. They are small and clean, and a number can be packed away in a case of small dimensions, so that a portable battery is at hand. They are really modified Leclanche ceUs, in which the solution of salammoniac is replaced by a moist, pasty composition. They tend to run down very slowly even if they are not used, but they will last from six months to two years if their use is not excessive and the best types are used. The battery of dry cells in the portable cases can be replaced when exhausted, and some makers allow 50% of the original price for the old cells in exchange for new ones. These dry ceUs can be obtained from most electrical dealers. Leclanche cells have an E.M.F. of about 1-5 volts when new, and their internal resistance is from 75 to 1*5 ohms — the smaller the ceU the higher the internal resistance. They are now almost universally used in portable batteries. Accumulators. — ^Accumulators, or storage batteries, as they are often called, are the most satisfactory means we possess of obtaining electricity from chemical ACCUMULATORS 271 action. The name " storage battery " is not correct. We do not store electricity in an accumulator, but if we take one that is run down and drive a current through it in the opposite direction to the current it gave out when working, we can restore the plates to their original condition and so give it a new lease of hfe, so to speak — ^and so long as we do not charge or discharge the cell at a greater rate than that for which it is designed, this process can be repeated almost indefinitely. An accumulator consists of a vessel containing sulphuric acid diluted till its specific gravity is 1200. In the acid are immersed lead plates made in the form of grids. Two of these plates are negative, one positive. The spaces of the grids are filled with a paste composed of htharge in the case of the negative plates, and red lead in the case of the positive. The plates lie close together, face to face, without touching. The internal resistance of an accumulator cell is extremely low. Each cell gives 2 volts under ordinary working conditions and continues to do so until about 75% of its charge is spent. If the cell be discharged still further the voltage begins to fall. It should never be allowed to faU below 1*8, nor should it ever be left at this latter figure for any length of time ; it should be recharged at once. If this be neglected, a white deposit appears on the plates — ^insoluble sulphate of lead. This increases the internal resistance and diminishes the capacity of the ceU, and it may be safely stated that a cell which has once become markedly sulphated can never be restored to its original condition. All cells have a certain rate of charge and discharge, which depends on the size and capacity, and which should never be exceeded. The charging current is usually about 10% of the fuU capacity. That is, a sixty-ampere- hour cell should not be charged with a greater current than 6 amperes. This, continued for ten hours, would fully charge the cell. 272 ESSENTIALS OF MEDICAL ELECTRICITY The charging of an accumulator should be continued until the voltage rises to 2*5 volts per cell. The voltage remains at this for a short time only after charging is stopped, when it declines gradually to 2 volts. Accumulators are also known as " secondary batteries " in contradistinction from the " primary batteries " as those previously described are often called. Primary batteries cannot be recharged like secondary batteries when exhausted. Bichromate Batteries. — For cautery and working large spark coils the bichromate battery is the most easily managed where some form of primary cell must be used. The plates are of zinc and carbon. They should be of large size, placed close together to reduce the internal resistance to its lowest limit, and arranged so that they may be readily removed from the exciting fluid the moment the current is no longer required. The zincs must be kept weU amalgamated. The exciting fluid is prepared as follows : — i pound of potassium bichromate is dissolved in 8 pounds of hot water. Then add slowly 2J pounds of strong sulphuric acid, stirring constantly all the time. While still hot, dissolve in the mixture 3 ounces of bisulphate of mercury. Each cell, when freshly charged, has an E.M.F. of 2 volts, but this tends to decline as the ceU is used — due to the gradual weakening of the exciting fluid. When this becomes green in colour it should be thrown out and fresh solution put in. These cells should be thoroughly washed and cleaned every three or six months, according to size, and care taken to remove aU the crystals of chrome alum which will be found sticking to the plates and acid vessel. The' zinc plates are gradually dissolved as part of the action of the cell and will eventually have to be replaced. This is not difficult in most forms now obtainable. ELECTRO-MOTIVE FORCE 273 The current produced in the ways described — i.e. by chemical means — ^is known sometimes as the " galvanic " current, sometimes as the " constant " current, by reason of its unvarying direction and uniformity of strength. The " direct " current is also a constant current, but the name " direct " is usually applied to it when it is obtained from the main. Electrical currents can also be obtained by mechanical methods. These will be described shortly. The Measurement of Electrical Currents. — ^This is a subject of great importance in the application of electri- city for treatment and diagnosis. During the flow of the current electricity is constantly passing along the circuit, and the terms " strong " or " weak," as applied to the current, are used in reference to the quantity of electri- city that is passing. The strength of an electrical current depends upon two factors : (i) the electro-motive force and (2) the resistance of the circuit. These terms will be explained. Electro-motive Force. — Whatever produces or tends to produce a transfer of electricity is called electro- motive force. Thus, when two electrified conductors are connected by a wire, and when electricity is trans- ferred along the wire from one to the other, the tendency to this transfer which existed before the introduction of the wire and which, when the wire is introduced, produces this transfer, is called the electro-motive force from the one body to the other along the path marked out by the wire. The water analogy will perhaps help to make this clearer. If two vessels containing water be joined by a pipe and we increase the pressure in one of them, the water will flow from the one in which the pressure is greater until the pressure in both becomes equal. Again, if the water is at a higher level in one vessel than in the s 274 ESSENTIALS OF MEDICAL ELECTRICITY the other, it will flow from the former to the latter until the level is the same in both. In the same way when any two electrified bodies are joined together by a wire, electricity will flow from the body on which the charge exists at high potential to the body on which the charge exists at lower potential. The inherent force which starts and maintains the current is what is known as electro-motive force — briefly written E.M.F. The potential of the earth is always taken as the zero of electric potential. The unit of E.M.F. is the "volt." A single Daniell cell produces an E.M.F. that is very slightly greater than one volt. Resistance. — ^It has already been mentioned that different substances vary enormously in their power of conducting electricity, some conducting it readily, others so badly that they are practically non-conductors or insulators. However well a substance conducts electri- city there is always some resistance to the flow. The resistance of a conductor depends on certain conditions. It varies {a) Directly as the length. {b) Inversely as the area of the cross section. (c) With the nature of the material of which the con- ductor is made. {d) To a certain extent with the temperature. {a) and (b) are sufficiently obvious. With regard to (c), a conductor made of silver is found to have a lower resistance when compared with one made of any other material of similar shape and size. The resistance of copper is very slightly greater than that of silver. Platinum has a resistance about six times greater than that of silver and iron about nine times greater. As a rule alloys have a resistance much greater than OHM'S LAW 275 pure metals. An alloy known as German silver has a resistance about fourteen times greater than that of silver, while another called rheostene has about forty-four times the resistance of copper. Speaking generally, the resistance of metals increases with an increase in temperature. Carbon and aqueous solutions of salts, acids and bases decrease in resistance as the temperature rises. In speaking of resistance it is useful to have a unit so as to be able to compare the resistance of various circuits or the different parts of a single circuit. The unit of resistance is called the "ohm," after the scientist who formulated the law which is known by his name. An ohm is represented by the resistance of a column of pure mercury at 0°C. of a uniform cross section of one square millimetre and 106 centimetres long. The Unit of Current. — ^The unit of current is the " ampere." It is the current produced when an electro- motive force of I volt acts through a resistance of I ohm. The strength of a current depends upon the electro-motive force and resistance. If the electro-motive force is increased, the current will be increased ; if the resistance is increased, the current will be diminished. In other words, increase of the force that produces the transfer of the electric fluid (or electrons) will cause a larger quantity of electric fluid (or electrons) to pass along the circuit, while increase of the resistance to the passage of the fluid (or electrons) will lessen the quantity of fluid (or electrons). The relation between strength of current, electro- motive force and resistance is stated in Ohm's law. Ohm's Law. — Ohm's law is as follows : — The current varies directly as the electro-motive force and inversely as the resistance. 276 ESSENTIALS OF MEDICAL ELECTRICITY Expressed in symbols it is : c = ^ where c = The current. E = Electro-motive force. R = Resistance. From the above equation we obtain E = CR and ■< = ? so that with any two of the factors given, the value of the third is obtainable by a simple calculation. This is probably the most important law that has been laid down relating to electricity, and is one that the student should be thoroughly familiar with it in all its aspects. It underlies every intelligent application of the electrical current in mediciue. Other Practical Units. — (i) Unit of Quantity. — ^This is the " coulomb " and represents the quantity of electri- city corresponding to a current of i ampere flowing for one second. (2) Unit of Work. — The unit of the work done is known as a watt. It is the product of the volts and the amperes. A current of i ampere at a pressure (E.M.F.) of i volt flowing for one hour is called one watt hour. The Board of Trade unit, as used by all supply companies, is 1000 watt hours. A current of 10 amperes at 100 volts flow- ing for one hour represents 1000 watt hours, for which the usual charge is sixpence. This is not a unit used in medical electricity, but, as many will obtain their supply from the street mains, it is as well to know what a Board of Trade unit really means. (3) Unit of Capacity. — It was previously mentioned INTERNAL RESISTANCE 277 that the capacity of a conductor was measured, not by its surface area, but by the quantity of electricity required to raise its potential from zero to unity. If a coulomb is required to raise the potential of a conductor i volt, that conductor is said to have a capacity of i farad. The size of such a conductor would be so enormous that the microfarad — that is, one-millionth of a farad — is taken as the unit of capacity. Internal Resistance. — This refers to the resistance to the flow of current inside a generator or originator of an electro-motive force. In the case of a dynamo-electric machine it is the resistance of the copper conducting wires with which the machine is wound — and in the case of the battery it is the resistance of the solution between the plates. In the former case it depends on the length and size of the wires ; in the latter, on the nature of the solu- tion, the area of the plates, and their distance from each other. For a generator to produce a large current it is essential that its internal resistance be kept very low. A resistance inside a cell has to be overcome just the same as if it were in the external circuit, and where the external resistance is very low, a high internal resistance would have a very serious effect on the output of current. On the other hand, with a very high resistance in the external circuit the internal resistance does not signify very much on account of the small proportion it bears to the total resistance of the circuit. To take an example : if the internal resistance of a cell be 3 ohms, and the resistance of the external circuit be i ohm, three-fourths of the E.M.F. of the cell will be used up in overcoming its own resistance, leaving only one-fourth of the original E.M.F. available for the outer or useful circuit. If, again, the internal resistance be the same, and the external resistance be 97 ohms, then only -^ of the E.M.F. will be used up inside the ceU, leaving -^-^ available for the 278 ESSENTIALS OF MEDICAL ELECTRICITY outer circuit. In the first example 75% of the total E.M.F. was wasted in the cell, in the second only 3%. Arrangements of Cells. — ^If we have a number of cells of any kind we can join them up in various ways to suit our requirements. Suppose we have twelve ceUs, each of which is capable of supplying a current of i ampere at an E.M.F. of i volt. It will be more convenient for the sake of clearness to assume that the cells have no internal resistance. We will also suppose that we have a 12-volt incandescent lamp with which we wish to examine some part or cavity of the body. This lamp requires an E.M.F. of 12 volts to bring it to full incandescence. To obtain this we join the positive pole of the first cell to the negative of the second, and the positive of the second to the negative of the third, and so on to the end of the row, so that we have a free positive pole at the first ceU, and a free negative pole at the twelfth, thus : — Fig. 65. — Diagram of Twelve Cells joined in Series If we now connect a volt -meter to the two wires from the ends, the instrument wiU register 12 volts, and if we replace the volt-meter by the lamp it will light up to its full candle-power. The cells as arranged above are said to be connected in series, and the effect of the arrangement is to increase the voltage directly as the number of cells — ^the total E.M.F. being equivalent to the E.M.F. of one cell multiplied by the number of cells. It does not increase the number of amperes beyond what is available from a single cell — that is, I ampere, which is probably more than the lamp requires. Now suppose we have a cautery which has a resistance of y\ ohm and requires a current of 12 amperes to bring it to the proper heat. It is quite ARRANGEMENT OF CELLS 279 clear that the series arrangement will not do, as the amount of current available is quite insufficient to affect the cautery. Also it will be seen that an E.M.F. of i volt is all that is necessary to send a current of 12 amperes through a resistance of ^^ ohm. Thus we have no object in increasing the voltage beyond that given by one cell, but the amperage of the current must be increased till it reaches 12. We now join all the positive poles together and do the same with the negatives, thus : — Fig. 66. — Diagram of Twelve Cells joined in Parallel + The result here is the same as if we had one big cell twelve times the capacity of a single cell. The voltage of any given cell is the same whatever the size, but the larger the cell the greater the quantity of current it is capable of suppling. We will now find that the differ- ence of potential between the terminals of the arrange- ment is just I volt, but a current of 12 amperes can be obtained, so that if we connect up the cautery it will glow a bright red and be ready for use. The cells connected as above are said to be arranged in parallel. Various combinations of the series and parallel arrange- ments are also possible. If we wanted a current of 2 am- peres at a pressure of 6 volts,' we would arrange the first six cells in series, and also the second six cells in the same way, and then join these two sets in parallel. This is a series-parallel arrangement — other modifications of which will suggest themselves. Current Density. — ^When a current flows along a narrow conductor its density or " concentration " will be greater than that of the same current when it flows along a broad conductor. The density of a current in one 28o ESSENTIALS OF MEDICAL ELECTRICITY conductor is the strength of the current divided by the cross-sectional area. It is of great importance, when apply- ing currents to the body, to avoid too great a density. The amount of current that the body can tolerate depends upon the degree of stimulation of the sensory nerve - endings in the skin and the force of contraction of the underlying muscles. The greater the density, the stronger the stimulation and the more violent the con- traction. So if the current enters and leaves the body through small electrodes, only weak currents can be passed. If we wish to employ large currents we must use large electrodes, and see that they are weU adapted to the part . For example, if we wished to apply a current of 50 milUamperes to a limb, and used electrodes, say, one square inch in area, the patient would experience a very sharp pain at the points of contact, and if the appHcation be persisted in for some minutes, a blister or even an ulcer will eventually form. The reason is that the whole 50 milliamperes passes through an area of one square inch. If we use larger electrodes, say five inches by five inches, the current density, instead of 50 milliamperes per square inch, would be only 2 milliamperes per square inch. In this way we can employ the same amount of current without discomfort or harm to the patient. Electric Current and Magnetism. — ^There is one other peculiar manifestation of electricity when passing through a conductor that has not yet been mentioned. If we take a wire through which a strong current is passing, dip it into some iron filings and then remove it therefrom (the current still flowing), some of the filings will be found attached to the wire, and will not all fall off when the wire is shaken, but if we stop the current flow- ing they all fall away at once, and so long as the current is not flowing the wire will not pick up any more. The reason for this is," that when an electric current flows MAGNETISM 281 through a wire there is always a field of magnetic force surrounding it. The lines of magnetic force are at right angles to the direction of flow of current. This magnetic field is a necessary accompaniment of an electric current, and is inseparable from it. It is the presence of this magnetic field which causes the magnetic needle to be deflected in the way to be described later. The Magnetic Needle. — ^If a straight piece of hard steel wire, such as a knitting needle, be magnetised, and sus- pended so as to be free to move in any direction, it will gradually come to rest, with one end pointing to the north and the other to the south. These ends are called the North Pole and South Pole respectively, and one is a necessary accompaniment of the other. That is to say, if we take any piece of magnetic substance, one end of which shows the presence of magnetism of the north variety — ^then the other end will be also magnetic, but of the south variety. If we take a bar magnet and cut it through at the middle where the magnetic attraction seems weakest or even lost, the result is two complete magnets, each having a north and a south pole. The knitting needle arranged as above is merely another form of compass, and both are really bar magnets. Properties of Magnets: Attraction and Repulsion. — Magnets possess properties analagous to those of electri- fied bodies. Like magnetic poles repel one another ; unlike poles attract each other. A magnet is also able to induce magnetism in a piece of iron or steel that is brought near to it without actually touching it. Any one pole of a magnet wiU induce magnetism of an opposite kind in that part of the iron that is nearest to it, and of the same kind in that part that is farthest away. It is for this reason that magnets attract particles of steel or iron. Magnetism is induced in them — that of the same 282 ESSENTIALS OF MEDICAL ELECTRICITY kind being farther off than that of the opposite kind, so that the particles are attracted with a greater force than that with which they tend to be repelled. It will be remembered that electrified bodies also attract other light bodies, because changes are induced on them. Lines of Magnetic Force. — ^Particles of iron or steel and magnetic needles, when brought into the neighbourhood of a magnet, at once arrange themselves in definite lines. / // / ! / / .,?m H Fig. 67. — Lines of Force around a Bar Magnet Magnetism is induced in them, and they take up posi- tions determined by the resultant of the attracting and repelling forces. The lines along which the magnetic induction acts are known as the " lines of magnetic force." As the pole of a magnet is approached, the force of induction increases and we speak of an increased number of lines of force in the region of the poles. A magnet is surrounded by lines of force. Fig. 67 shows a bar magnet with the surrounding lines of force. If two magnets are brought into the neighbourhood of one another they tend to arrange themselves so that their lines of force assume the same direction where they overlap. If a magnetic needle is suspended it sets itself north and south, so that its own lines of force GALVANOMETER 283 — ^the majority of which lie between its two poles — may coincide with those of the earth. It has been mentioned that a wire along which a current is flowing is surrounded by a magnetic field. The lines of force have a definite direction. They are arranged concentrically around the wire conveying the current in a plane at right angles to it. If a magnetic needle is placed close to a wire along which a current is flowing, the north-south direction previously taken under the influence of the earth's magnetic lines is now altered by the new magnetic lines created by the current. The magnetic needle now alters its direction so that its own lines of force can coincide as far as possible with those created by the current. The position which the north- seeking pole of the needle will assume can be foretold if the following illustration is remembered : — Imagine a man swimming in the wire in the same direction as the current and turned so as to face the needle, then the north-seeking pole of the latter will be deflected towards his lejt hand. The Galvanometer. — ^This is an instrument designed for the measurement of electrical currents. An ampere- meter (or ammeter) is a galvanometer graduated so as to indicate on its scale the number of amperes passing through it. A milliampere-meter indicates the current in thousandths of an ampere, i milliampere being y^Vo^^ of an ampere. A volt-meter is a galvanometer that measures electro- motive force. These instruments work on the principles described above ; the current causes the deflection of a movable magnetic needle, and the amount of deflection is the measure of the strength of the current. Until comparatively recently all galvanometers were of the magnetic needle type. While undoubtedly 284 ESSENTIALS OF MEDICAL ELECTRICITY accurate, they laboured under certain disadvantages. They had to be carefuUy levelled, and placed in proper relation to the magnetic meridian to bring the pointer to zero. The latter always took some time to come to rest, and the readings were easily disturbed by the presence of magnetic bodies near by. It is not necessary to refer to them further, as they are being displaced by instruments of the " moving coil " type, one of which is shown in Fig. 68. Whereas in the original form of instrument the magnetic needle was movable and the wire conveying the current stationary, in the moving-coil form the reverse arrange- ment is seen. The magnet — ^which is U-shaped — is station- ary, and between its poles is the coil of wire that conveys the current. This coil is movable and to it is attached an indicatoi t^^ that moves over a scale calibrated to indicate the number of milliamperes. These instruments read accurately in any position, are quite independent of the earth's magnetism or the presence of magnetic bodies, and they are " dead beat " — that is to say, the pointer quickly indicates the amount of current passing, without first swinging to and fro for some time. The instrument shown reads to 15 miUi- amperes. As this is too small for some purposes, it is provided with one or more shunts, which can be switched on or off as desired. The principle of the shunt is that when a current has two paths in which to flow, Fig. 68. — Milliampere-meter " Moving Coil " Type MILLIAMPERE-METER 285 it divides itself between the two, so that the current strength in each path is inversely proportional to its resistance. The arrangement is shown diagrammatically in Fig. 69. As there shown, all the current that passes through the instrument will flow through the coil which causes the needle to move. The resistance of the shunt marked 10 is so adjusted that when it is brought into circi^ -^Q of the total current passes through it, and —^ through the coil controlUng the needle. Therefore the total current passing will be ten times that indicated by the instrument. If the other shunt is used the readings are to be multiplied by 100. The knob on the top of Fig. 68 is for switching the shunts in or out of circuit. As it is re- volved, the figures i, 10, 100 pass in suc- cession behind a small opening in the top of the dial, indicating which Fig. 69.— Arrangement of Shunts in Shunt is in circuit. In Milliampere-meter some instruments, however, the figures indicate the maximum current recorded when that particular shunt is in circuit. In the instrument shown in Fig. 68, the number 150 is shown, and it means that the instrument now records between zero and 150 milliamperes. When the zero is showing it means the whole instrument is out of action. In this position it is impossible for the instrument to be injured by the accidental passage of a heavy current through it, which would probably cause serious, if not irreparable, damage. Shunted instruments are very little more expensive than plain i—wHwrnmiQ 286 ESSENTIALS OF MEDICAL ELECTRICITY ones, and should always be selected when buying an outfit. The Electro-magnet. — ^It was shown that a wire carry- ing an electric current became magnetic and would attract iron filings. If we take a piece of soft iron rod and wrap this wire around it, it will impart its magnet- ism to the iron, which will become strongly magnetic, especially if the wire is wrapped many times round and a strong current sent through it. This arrangement constitutes an "electro-magnet." An electro-magnet is only magnetic when an electric current is traversing its wire helix, provided the core — as it is called — ^is com- posed of sojt iron or soft steel. Magnets on this principle can be made capable of hfting many tons' weight. They lose their magnetism entirely when the current is cut off. If the core should be made of very hard steel, a portion of the magnetism remains after the current is cut off. This core may be removed from the centre of the wire winding, and will retain more or less of its magnetism indefinitely. In this way permanent magnets are made. Electro-magnetic Induction. — ^The first observations of this most interesting and important subject were made by Faraday. He found that in a closed circuit an electric current of momentary duration is induced when a magnet is approached to this conductor or withdrawn from it. He also found that if a current were made to pass through another circuit near, but quite detached from, the first one, a momentary current passed through the latter, both when the current started and when it was interrupted. The current is produced by virtue of the magnetic field set up and removed in the neighbourhood of the original closed circuit. These induced currents, as they are called, only appear so long as the magnetic field is varying in strength. The current induced at the starting of the inducing current is in an opposite direction to the latter, while that SELF-INDUCTION 287 produced when the inducing current is interrupted is in the same direction as the inducing current. It will thus be seen that whether we use a permanent magnet, an electro-magnet or a length or coil of wire carrying a current for our purpose, so long as we subject a closed circuit to a varying field of magnetic force, currents of electricity are set up in the closed circuit. These currents wiU vary in direction of flow according as the magnetic field is increasing or decreasing in strength. Simple as the fundamental principle of the induction of currents is, it is perhaps the most important of all as regards the practical appHcations of electricity. The dynamo, motor, induction coil, telephone, etc., are all based on the principle of electro-magnetic induction. Self-induction. — Take a length of insulated copper wire, say two or three yards, straighten it out and attach one end to one terminal of a cell possessing high internal resistance, such as a Leclanche ceU. Bring round the other end (both ends must be stripped of their insulating covering for an inch or so) and touch the other terminal of the cell with it for a moment. A very tiny spark will be seen at the instant the wire leaves the terminal. It may be necessary to do this experiment in a darkened room, so small is the spark. Now coil up this length of wire into a close spiral by winding it on a ruler, and repeat the experiment. At the moment when the circuit is broken and the current ceases to flow, a spark that is distinctly brighter will be seen at the point where the circuit is interrupted. This is the result of the induction of new currents in the turns of the spiral at the moment the original current ceases to flow. These new currents flow in the same direction as the latter, and so reinforce it. A brighter spark is therefore produced. At the moment when the circuit is completed, new currents are again induced, but these flow 288 ESSENTIALS OF MEDICAL ELECTRICITY in a direction opposite to that of the original current, and so weaken it. The weakening is only momentary, because the induced currents flow only for a moment, and therefore all that they do is to retard the rise of the original current to its full strength while they are flowing. The development of induced currents in the same circuit as that in which the inducing current is flowing is spoken of as " Self-induction. " If we introduce a rod of iron into the spiral, and the experiments are repeated, the effects described above will be further increased. Stronger currents will be induced at make and at break of the circuit and wiU further weaken the inducing currents at make and further reinforce it at break. We can vary the amount of this self-induced current by increasing or decreasing the number of turns in the spiral, by varjdng the strength of the original current, and by inserting or withdrawing an iron core. The Alternating Current. — ^The current of which we have been speaking up to the present is the constant current, the current that is flowing continuously always in the same direction and with strength unvaried. An alternating current is one that is constantly reversing its direction of flow. The reversals may be rhythmic or arrhythmic, regular or irregular, gradual or abrupt, frequent or infrequent. Fig. 9 (p. 23) is a graphic repre- sentation of an alternating current of which the reversals are rhythmic, regular, gradual and frequent. When an alternating current is spoken of without further quaUfi- cation it is usually understood to be of the type repre- sented in the figure. From A io B the current rises from zero to its maximum ; from ^ to C it falls again to zero. From C to D the current again rises from zero to maximum ; from D to £^ it falls again to zero. From C to £ the current is flowing in the opposite direction. The complete course, from A to E, is spoken of as one ALTERNATING CURRENTS 289 complete cycle or phase. The height of the curve above the base line at any one spot is proportional to the voltage and the length along it to the time intervals. The alternating current is produced by a dynamo, and it will be seen in the next paragraph how it is generated. These currents are frequently named " sinusoidal," because their graphic representation is approximately a sine curve. In many districts the town A r^ CD Fig. 70 — To illustrate way in which an Alternating Sinusoidal Current is produced supply is an alternating current (AC). In others it is a constant or " direct " crruent (DC). The Production of Alternating Currents. — ^When a coil of wire is made to revolve in a magnetic field an electrical current will flow round the coil. On this principle currents are generated by the dynamo.- In Fig. 70 (A), a magnet is shown, and between its poles is a single coil of wire. This coil rotates in the mag- netic field between the poles of the magnet. During its rotation, when it is in the position shown in the figure (A), equidistant from both poles, no current flows around it. During its rotation through a right angle (one quarter of a complete revolution) a current flows around it, start- ing from zero, its strength gradually increasing and T 290 ESSENTIALS OF MEDICAL ELECTRICITY attaining its maximum value when the coil has the position shown in Fig. 70 (B). During the next quarter of a revolution the current gradually falls again to zero. During the third quarter the current again increases to a maximum, and during the fourth quarter it gradually reaches zero again. The current that flows during the last two quarters of the revolution is in the reverse direction. For the first half of the revolution the current is in one direction ; for the second half it is in the opposite direction. During each half it starts from zero, reaches a maximum and again falls to zero. This current is the alternating current described in the previous paragraph, and may be graphically represented, as in Fig. 9. The curve shown, ABCDE, corresponds to one complete revolution of the coil. The number of these complete cycles per second depends upon the rate of revolution of the coil. The " frequency " or " periodicity " of an alternating current refers to the number of these complete revolutions per second. Thus if the periodicity of the current is 100, the coil is revolving 100 times per second ; the length of the curve recording one complete cycle would be yJir'th of a second, and there would be 200 reversals of direction (or alternations) each second. While it is possible to evolve a sinusoidal current from an ordinary battery, we may say that all alternating currents have their origin in dynamo machines. The number of cycles per second — i.e. the frequency— of these currents used to be 100 to 130, but of late, lower frequencies have become more common — from 40 to 60. The Dynamo. — It may be said that over 99% of the electricity used for various purposes is obtained from dynamos. By far the most convenient source of electri- city for medical purposes is the dynamo at the power station, from which the supply is taken along the mains DYNAMO 291 to the places where it is desired. In places where there is no main supply, the current may be derived from a small dynamo worked by a gas or oil engine or by Water- power. The device which has been described above for the production of an alternating current is really a dynamo in a very simple form. A dynamo consists of three essential parts : (i) the field magnet ; (2) the armature ; (3) the current-collecting device (Fig. 71). (i) The Field Magnet, which generally forms part of the framework of the machine, is usually an electro- ARMATURE BRUSH ^ _ " ARMATURE COMMUTATOR •<■ " FIELD MAGNET FIELD MAGNET COIL Fig. 71. — Dynamo constructed to generate a Direct Current magnet, the poles of which have their opposing faces hollowed out to the arc of a circle, in which space the armature revolves. When the field magnet is excited this space will be th^ seat of a powerful magnetic field. The essential point about the field magnet is that its poles never change ; one is always north and the other south. (2) The Armature is the part of the dynamo in which the current is induced by reason of its movement in the magnetic field. In the simple device shown in Fig. 70 it was a single circuit of wire. The armature of a dynamo that generates alternating currents consists of an axle 292 ESSENTIALS OF MEDICAL ELECTRICITY surrounded by strips of soft iron, upon which are wound several turns of insulated copper wire. The free ends of this* wire are connected to the current-coUecting device. The armature of a dynamo that is to generate a current that flows in the same direction and with constant strength (the constant current, or direct current) con- t ains several separate coils. (3) The Current- collecting Device. — ^If an alternating current is to be collected the device consists of two metal rings mounted concentrically on the axle of the armature. They are insulated from each other and the axle. To one of them is fixed one of the free ends of the wire wound round the armature, to the other ring is fixed the other free end. A carbon " collecting-brush " presses against each ring and leads the current to the main circuit. As the axle of the armature revolves, the rings revolve with it, and the carbon brushes coUect the current from the rings. The current collected is an alternating current. If a constant (direct) current is to be collected the collecting device (called in this case a " commutator ") consists of a number of copper bars mounted in the form of a cylinder, and insulated from the shaft and from each other. There are as many bars as there are coils on the armature. The beginning of one coil and the end of the coil just preceding it are joined together, and the two are attached to a commutator bar. Two brushes of copper gauze or carbon press against the revolving cylinder and collect the current (see Fig. 71). Dynamos and Motors: Motor Transformers. — The dynamo that generates a direct current is a reversible machine. That is to say, if another direct current is sent through the armature, the latter will revolve. The dynamo, therefore, now acts as a motor, converting MOTOR TRANSFORMER 293 electrical into mechanical energy. Motors are also con- structed so as to work when supplied by an alternating current. Electric motors are used in medicine for several purposes, for working drills and trephines, for applying massage and vibration, etc. Electric motors are used for another purpose. They can be used to work dynamos constructed to generate a new current of a kind different from that which works the motor. A combination of a motor and dynamo for this purpose is called a "motor transformer." A motor transformer is an exceedingly useful machine and is extensively used now in electro-medical work. It serves the following purposes : — (i) A constant (direct) current — from the main or from accumulators — can be converted into an alternating (sinusoidal) current. (2) An alternating current can be converted or trans- formed into a direct current. (3) By combining a motor and a dynamo it is possible to convert a direct current at a high voltage into another direct current at lower voltage. By such an arrangement the circuit in which a patient is placed can be kept dis- tinct and separate from the main circuit, so that the risk attending the use of the direct current from the main for medical purposes is avoided. A motor transformer is constructed on the following plan : — On the lengthened axis of a motor is fixed another independent armature, which revolves between the poles of another field magnet. The armature and the current- collecting device can be arranged so that the new current is either alternating or direct, while the number of turns of wire on the armature will determine the voltage and amperage of the new current. It is not essential to have an independent field magnet and armature. The other armature may have two separate sets of windings on it, forming a double 294 ESSENTIALS OF MEDICAL ELECTRICITY armature, and the same magnetic field will serve for this double armature. Static Transformer.— A motor transformer can be used for the purpose of converting an alternating current into another alternating current with a different voltage and laOHCOfi^ SbcondaryCoil Fig. 72. — Plan of a Static Transformer amperage, but a much more efficient and less costly apparatus for the purpose is the " static transformer." It is called a static transformer because there are no moving parts. It consists of a core of soft wire made in the form of a ring or a square (Fig. 72). A coil of insulated wire is wound around one side. Another independent coil, also of insulated wire, is wound on the opposite side. The alternating current is led through one of these coils. As it alternates backwards and forwards a varying magnetic field is set up in the core ; as a result, new STATIC TRANSFORMER 295 alternating currents are induced in the other coil. The latter coil is known as the secondary coil, to distinguish it from the other coil, which is known as the primary coil. The voltage and amperage of the current that is induced in this secondary coil depends on the number of turns it contains as compared with the number of the primary. To take an example. Suppose that the primary coil has 100 turns of wire and that the alternating current supplied to it has a pressure of 100 volts, and that we wish to obtain a current to heat a cautery which requires a pressure of, say, 5 volts. The primary has one turn per volt and theoretically the same will be right for the secondary — in this case five turns. It will be found that this will come out about right, and if the wire of the secondary has been chosen sufficiently thick plenty of current will be available for even the largest cautery used in surgery. A transformer regulates itself in a most perfect manner. As we draw off current from the secondary this relieves the primary of so much of its self-induction, and consequently more current flows in. In a well-designed transformer very nearly the same amount of energy is available from the secondary side as is supplied to the transformer on the primary side. Supposing we have one which is designed to take 10 amperes at 100 volts through the primary. This is equivalent to 1000 watts. Accord- ing as the secondary is wound we can have from it 200 amperes at 5 volts, i ampere at 1000 volts, or o-i ampere at 10,000 volts. The alternating current transformer is the most efficient instrument we possess. For those who have an alternating current available, a transformer which will give any voltage desired is a most useful appliance and will well repay any trouble or expense incurred in obtaining it. INDEX Accumulators, 270 ; construc- tion of, 271 ; charging of, 59, 271 Acne Vulgaris, 214 Acroparsesthesia, 215 Action of electricity on tissues, 3 et seq. Alopecia, 215 Alternating current, 21, 23, 288 ; production of, 289 ; periodicity of, 290 Aluminium rectifier, 51 Amenorrhcea, 215 Ampere, 275 Ampere-meter (ammeter), 283 Ampere-meter, hot wire, 167 Anal fissure, 215 Aneurysm, 97, 215 Anode, 68 Anodic closure contraction, 143 Anterior poliomyelitis, 218 Antrum, ionisation of, 84 Aphonia, 216 Apostoli, method of, 96 Arm, palsy of, 129 Arm baths, iii Armature of condenser, 261 ; of dynamo, 291 Arrangement of cells, 278 ; in series, 278 ; in parallel, 279 Arthritis, 216 ; gonorrhoeal, 217 ; gouty, 217 ; osteo-, 218 ; rheumatoid, 217; traumatic, 216 Asthma, 219 Ataxy, Locomotor, 232 Auto-condensation couch, 169 Auto-conduction, 170 297 Baker electric machine, 199 ; field regulator, 206 Bar magnet, 281 Bath, electric, iii et seq. (see also Electric Baths) ; Schnee, 112 Bipolar electric bath, 114 Bipolar electrolysis needles, 92 Blood-pressure, high, 228 ; low, 13, 210 Boils, 219 Bougie electrode, 95 Breeze, static, 208 Brush, static, 208 Capacity, 260 Carbuncle, 219 Carcinoma, 219 Cardiac failure, 220 Cataphoresis, 71 Cell, bichromate, 269-272 ; dry, 270 ; Leclanche, 269 ; Poggen- dorff, 269, 272 Cells, arrangement in parallel, 278 ; series, 278 Cerebral galvanisation, 9 Chemical changes produced by electricity, i-io, 14 Chilblains, 220 Chorea, 220 Closure contraction, 10 Coil, induction, 27 Colitis, 221 Collector, current, 62 Colon, ionisation of, 85 298 INDEX Commutator, of dynamo, 292 ; Ruhmkorft, 21 Compass needle, 281 Condenser, 261 ; couch, 169 ; discharge of, 161, 262 ; elec- trode, 171 Condensers, testing by discharge of, 158 Conducting cords, 77 Conduction of currents at high voltage, 70 ; through body, 4 ; through solution, 3 Conductors, 255 Congestion, 221 Conjunctivitis, Vernal, 248 Current, alternating, 23, 288 ; collector, 62 ; conduction through body, 4 ; solutions, 3 ; conduction at high voltage, 70 ; constant, 16, 273 ; continuous, 16 ; density of, 279 ; density of, in body, 67 ; direct, 16, 273 ; faradic, 26 ; for treatment of paralysis, 120 ; from main, 35 ; from main (direct), 36 ; from main (alternating), 46; dangers, 52 ; from main for baths, 49 ; from main for cautery, 42, 48 ; from main for lamps, 44, 48; galvanic, 16, 273 ; high-fre- quency, 161 ; measurement of, 273 ; modifications of, 16 et seq. ; Morton wave, 205 ; path in body, 66 ; production of, 264, 289, 290 ; simple alternat- ing, 21 ; simple interrupted, I 7 ; sinusoidal, 23 ; slow sinu- soidal, 25 ; sources of supply, 35 et seq. ; static induced, 212 ; static wave, 205 ; unit of, 275 Dangers in use of main current, 52 Density of static charge, 259 ; current, 279 Diagnosis, use of currents for, 138 et seq. Diathermy, 178 et seq. ; appa- ratus, 182 ; application to body, 185 ; coagulation of tissues by, 190 ; condenser couch for, 185 ; electrodes for, 187, 189, 191 ; general treatment by, 185 ; heating of deep parts by, 184 ; and innocent growths, 193 ; and inoperable growths, 192 ; and malignant growths, 192 ; and metabolism, 184; medical, 189 ; and operable growths, 193 ; physiological action of, 183 ; production of, 179 Discharge of Leyden jar, 161, 262 ; of condenser, 161, 262 Effluve, high-frequency, 170 Electric baths, 1 1 1 ; bipolar, 1 14 ; construction of, 11 1 ; currents for, 115; dangers of, 57; electrodes for, 114 ; full length, 113 ; how given, 115 ; pre- cautions in giving, 116; Schnee, 112 ; unipolar, in Electric supply, sources of, 35 et seq. Electrical reactions, testing of, 138 et seq. ; types of, 149 et seq. ; treatment, index of, 214 et seq. Electricity, nature of, 252 ; theories of, 253 Electrisation, general, 117 Electrodes, bougie, 95 ; con- denser, 171 ; diathermy, 187,- 189, 191 ; high-frequency, 171; paddle, 114 ; static, 201 ; static wave, 207 ; vacuum, 172 Electrolysis, surgical, 8, 88 ^/ seq.; linear, 96 Electrolytic incision, 96 Electro -magnet, 286 Electro-magnetic induction, 286 Electro-motive force, 273 Electrons, 253 Electroscope, 257 Endometritis, 225 INDEX 299 Enlargement of prostate, 244 Epididymitis, 241 Epilation, 89 ; needle, 90 Episcleritis, 225 Erb's point, 132 Ewing's reverser, 25 Exophthalmic Goitre, 226 Facial paralysis, 126 Farad, 261 Faradic current, 26 ; how pro- duced, 27 ; variations in, 30 Faradisation, general, 117 Fibromyomata, 96 Fibrositis, 226 Field m.agnet, 291 Fissure, anal, 215 Fistula, 226 Fulguration, 177 Furuncle, 219 Galvanisation, cerebral, 9 ; general, 117 Galvano-faradisation, 117 Galvanom.eter, 283 General faradisation, 117; gal- vanisation, 117 Generator, motor, 45 Goitre, exophthalmic, 226 Gonorrhcea, 226 Gonorrhoeal arthritis, 217 Gouty arthritis, 217 Growths, malignant, 97, 192, 233; innocent, 193 H HEMORRHOIDS (see Piles) Headache, 227 Hemiplegia, 227 High blood-pressure, 228 High-frequency currents, 161 et seq. ; action of, 174 ; appara- tus for, 163 ; application, 168 ; High-frequency currents- contd. and ionic movement, 11 ; meaning of , 11, 161 ; measure- ment of, 167; and metabolism, 175 ; mode of action of, 12 ; oscillations, 161, 263 ; in surgery, 176 ; and vascular system, 175 High-frequency effiuve, 170 ; electrodes, 171 Holtz electric machine, 198 Hot-wire ampere-meter, 167 Hypertrichosis, 228 Hysteria, 229 Incision, electrolytic, 96 Incontinence of urine, 229 Induced current, 286 ; static, 212 Induction coil, 27 ; currents in, 29 ; designs of, 32-34 ; out- put of, 29 Induction, electro-magnetic, 286 Infantile palsy, 134 Influence machine, 263 ; Baker, 199; Holtz, 198; mode of action, 264; Toepler, 199; Voss, 199 ; Wimshurst, 194 Injuries of joints, 216 Interrupter, 17, 19, 21, 25 Ionic medication, 70 et seq. ; advantages of, 72 ; apparatus for, 75 ; application of, 81 ; of colon, 85 ; conducting cords for, 77 ; current for, 76 ; of deep parts, 99 et seq. ; defini- tion of, 71 ; duration of, 86 ; electrodes for, 77 ; frequency of, 87 ; limitations of, 73 ; of maxillary antrum, 84 ; of rectum, 85 ; of sinuses, 83 ; solutions for, 79 ; surgical, 88 et sea. Ionic migration, 5, 8 Ionic movement as stimulus, 10 lonisation (see Ionic . Medica- tion) lonisation in deep tissues, 99 et seq. 300 INDEX lonisation, surgical, 88 et seq. Ions, 4 ; depth of penetration of, 74 ; direction of migration of, 5 ; introduction of, g ; migra- tion of, 5, 8 ; meaning of, 4 ; proof of entry, 72 ; those used in medicine, 81 JoiMTS, diseases of, 216 ; in- juries of, 216 K Kathode, 69 ; meaning of, 5 Kathodic closure contraction, 143 J Keratitis, 231 Lachrymal obstruction, 231 Leduc's interrupter, 19 Leyden jar, 261; discbarge of, 263 Linear electrolysis, 96 Locomotor Ataxy, 232 Longitudinal reaction, 152 Lupus Vulgaris, 232 Measurement of current, 283 ; voltage, 283 Median nerve, 131 Menstrual irregularities, 215, 225 Mental diseases, 234 Meralgia Paraesthetica, 234 Meta tarsalgia, 234 Metronome interrupter, 18 Microfarad, 276 Milliampere, 283 Milliampere-meter, 283 Mode of action of electricity, 3 et seq. Modifications of constant current, 16 Moles, 95 Monoplegia, 227 Monopolar baths, iii Morton wave current, 205 Motor, electric, 292 Motor generator, 45 Motor points, 142 Motor transformer, 45, 292 Multostat, 25, 45 Muscle, testing reactions of, 145 ; reactions of normal, 138 ; types of reaction of, 149 Myalgia, 235 Myasthenic reaction, 153 Myelitis, 235 Myotonic reaction, 152 N M Magnetic attraction and re- pulsion, 281 Magnetic lines of force, 283 ; needle, 281 ; poles, 280 Magnetism, 280 Magnets, lines of force of, 283 ; poles of, 281 ; properties of, 281 Main, current from, 38 et seq. Malignant growths, 97, 233 Maxillary antrum, ionisation of, 84 N^vus, needles for treatment of, 91, 92 ; treatment of, 91 et seq. Nerve trunks, testing of, 1 49 Nerves, peripheral, 124 ; reac- tions of, 149 Neuralgia, great occipital, 237 ; ovarian, 242 ; trigeminal, 236 Neurasthenia, 237 Neuritis, 237 ; alcoholic, 238 ; arsenical, 238 ; brachial, 239 ; optic, 242 ; rheumatic, 239 ; septic, 239 Nocturnal incontinence, 229 Non-conductors, 255 Normal reactions, 139 INDEX 301 o Obesiiy, 240 Occupation spasm, 241 CEsophageal spasm, 241 ; stric- ture (see under Urethral Stricture) Ohm, 275 Ohm's law, 275 Ophthalmia Neonatorum, 242 Optic neuritis, 242 Orchitis, 241 Oscillograph tracings, 30 et seq. Osteo-arthritis, 218 Oudin's resonator, 170 Ovarian neuralgia, 242 Ozaean, 242 Pantostat, 25, 45 Parallel arrangement of cells, 279 Paralysis Agitans, 242 ; of arm muscles, 129 ; changes in muscles in, 119 ; currents used in treatment of, 120 ; deltoid, 128 ; duration of treatment in, 124 ; electrical reactions in, 153 ; electrical treatment of, 118; Erb's, 131; facial, 126; infantile, 134 ; of lower limb, 133 ; median, 131 ; muscle changes in, 119 ; musculo- spiral, 129 ; of peripheral nerves, 129 et seq. ; of sciatic, 133 ; of serratus ma gnus, 128 ; of spina ti, 129 ; of sterno- mastoid, 127 ; of trapezius, 127 ; treatment of, 118 et seq. ; ulnar, 131 Paraplegia (see Hemiplegia) Partial reaction of degeneration, 151 Path of current in body, 66 Penetration of ions, 72 ; depth of, 74 ; proof of, 72 Perineuritis, 243 Peripheral nerve palsy, 124 ; in lower limb, 133 ; in upper limb, 125 Physical effects of electricity, 13 Piles, 243 Plate of voltaic cell, 268 ; posi- tive and negative, 268 Platform, insulated, 200 Pleurisy, 243 Polar reversal, 151 Polarisation, 269 ; prevention of, 269 Polarity of static machine, 202 Poles, magnetic, 281 ; negative and positive, 268 ; of voltaic cell, 268 Poliomyelitis, 218 Polystat, 25, 45 Portable battery, 61 ; shunt resistance, 40 Port- wine marks, 94, 244 Potential, 259 Practical units, 275, 276 Primary batteries, 60 ; coil, 27] Private installations, 58 Prognosis of RD, 156 Prostate, enlargement of, 244 Pruritus ani, 244 ; vulvaj, 244 R Raynaud's disease, 245 Reaction of degeneration, 151 ; appearance of, 155 ; complete, 151 ; course of, 155 ; meaning of, 153 ; partial, 151 ; prog- nosis of, 156 Reaction, longitudinal, 152 ; myasthenic, 153 ; Myotomi, 152 ; Rich's, 153 ; types of, 149 Reactions, of muscle, 138 ; of nerve, 138 ; normal, 139, 149 ; testing of, 138 et seq. ; weak normal, 150 Rectal fistula (see Fistula) Rectifier, chemical (aluminium), 51 ; mechanical (motor), 52 Rectum, ionisation of, 85 Refreshing action of current, 9 Resistance, 274 ; of body, 64 et seq. ; internal, 277 ; series, 37 ; shunt, 37 ; unit of, 275 302 INDEX Resonator, Oudin's, 170 Reyn's electrolysis, 232] Rheumatic neuritis, 239 Rheumatoid arthritis, I217 Rhumkorfi coil, 27 ; commuta- tor, 21 Rhythmic current interrupters, 17-23 ; ^resistance varyers, 106 Rich's reaction, 153 Rickets, 245 Rodent ulcer, 245 Sarcoma (see Malignant Growths) Scar tissue, 246 vSchnee bath, 112 Sciatica, 247 Sclerosis, disseminated, 224 Secondary coil, 28 ; current, 29 Self-induction, 287 Series, arrangement of cells in, 278 Series resistance, 37 Sexual disorders, 248 Shoulder, paralysis of, 127 Shunt resistance, 37 Shunts to milliampere-meter, 2,85 Simple alternating current, 21 Simple interrupted current, 17 Sinuses, ionisation of, 83, 248 Sinusoidal current, 23 ; slow, 25 Skin, resistance of, 64 Slow sinusoidal current, 25 Solenoid, 164 Sources of electric supply, 35 et seq. ; from accumulators, 59 ; from main, 35 et seq. ; from primary batteries, 60 ; from private installation, 58 Spark-gap, diathermy, 181 ; high- frequency, 164 Sparks, static, 210 Spasms, oesophageal, 241 ; oc- cupation, 250 Sprains (see Arthritis) Spring catarrh, 248 Static bath, 203 ; breeze, 208 ; brush, 208 ; charge and dis- charge, 205 ; electricity, 194, etseq. ; electrodes, 201 ; induced current, 212 ; machines, 194- 200 ; mode of action of, 13, 14 ; physics, 253 ; testing polarity, 202; sparks, 210; transformer, 47; 294 ; wave current, 205 Stellate veins, 94 Stiff joints (see Arthritis) Stimulation of tissues, 104 ; use of current for, 104 ; how pro- duced, 10 Stricture, treatment of, 95 ; urethral, 95 Superfluous hair, 89 Supply, sources of electric, 35 et seq. Surgical electrolysis, 8 ; ionisa- tion, 8 Switchboard, 39-42 Sycosis, 248 Synovitis, 248 Tabes (see Locomotor Ataxy) Testing polarity, 202 Testing reactions, apparatus for, 139 ; by condensers, 158 ; difficulties in, 157 ; defects of method, 158 ; how done, 141, 145 Thermal effects of electricity, Tinea, 249 Tinnitus Aurium, 249 Toepler machine, 199 Trachoma, 249 Transformer, motor, 45 ; static, 47, 294 U Ulcer, chronic non-specific, 249 ; corneal, 224 ; rodent, 245 Ulnar palsy, 130 Unipolar baths, 11 1 INDEX 303 Unit of capacity, 2 76 ; of current, 275 ; of E.M.F., 274 ; of re- sistance, 275 ; of work, 276 Universal apparatus, 25 Urethra, stricture of, 95 Urinary incontinence, 229 Uterine fibromyomata, 97 Variocele, 250 Veins, stellate, 94 ; varicose, 250 Vernal Conjunctivitis, 243 Volt, 274 Voltaic cell, 266 Volt-meter, 283 W Vacuum electrodes, 172 Variation of resistance, rhythmic, 106 Varicose, veins, 250 VvARTS, 94, 251 Watt, 276 Wimshurst machine, 94 Writer's cramp, 250 Henry Kimpton, 263 High Holborn, London, RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg.400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS • 2-month loans may be renewed by calling (510)642-6753 • 1-year loans may be recharged by bringing books to NRLF • Renewals and recharges may be made 4 days prior to due date. 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