ESSENTIALS OF MEDICAL ELECTRICITY A TEXTBOOK OF RADIOLOGY E, REGINALD MORTON M.D., C.M. (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 officer." 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-Eay Department, West London Hospital, etc. THIRD EDITION, REVISED AND REWRITTEN WITH ADDITION OF NEW MATTER BY ELKIN P. CUMBERBATCH, M.A., M.B., B.CH., OXON. Member of the Royal College of Physicians of London, Medical Officer in Charge of the Electrical Department, St. Bartholomew's Hospital, and late Demonstrator of Physiology in tht Medical WITH ELEVEN PLATES AND SEVENTY-TWO ILLUSTRATIONS ST. LOUIS C. V. MOSBY COMPANY 1916 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 dealing 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 STREET, 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 SUPPLY . ... 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 Currents 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 Kairs 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 Amenorrhcea 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 Dysmenorrhcea Endometritis Episcleritis Exophthalmic Goitre Fibrositis Fistula Gonorrhoea Headache Hemiplegia High Blood Pressure Hypertrichosis 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 GEsophageal Spasm Orchitis Ophthalmia Neonatomm Optic Neuritis Ovarian Neuralgia Ozasna 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 Measurement 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 I. -XI. Motor points and cutaneous areas .... Facing page 160 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 . . . . 17 4. Metronome Interrupter. Baird & Tatlock . 18 5. Plan of Commutator of Leduc . . 19 6. Leduc's Mechanical Interrupter. Newton & Wright . . . . .20 7. Ruhmkorffs 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 6- Co. . . . . -3 14. Graphic record of the Secondary Current. H. K. Lewis & Co. . . . .31 15. Lewis Jones' Coil. Schall 6- Son . .32 16. Sledge Coil. Schall 6- Son . . 33 xi xii LIST OF ILLUSTRATIONS PAGE 17. Current derived from main . . 36 1 8. Plan of Shunt Resistance. Schall 6- Son . 37 19. Shunt Resistance. Schall 6- Son . . 39 20. Morton Box. Schall 6- 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 may be 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 . . -78 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 6- Son . . 140 43. Testing Electrode. Cavendish Electrical Co. . 141 44. D'ArsonvaTs 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 & 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 & 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 e^ctricity and explanations of the terms in common use in Chapter XV. A I 2 ESSENTIALS OF 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 derelicts, 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 yield the best results the general treatment should not be neglected. There is, now, no region of the body to which electrical treatment is not applied, 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 pure and contains no salts in solution. The needle of the milli- ampere-meter wnl remain at zero. If now a salt such as sodium 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 sodium 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 will 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 electrolyte 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 (Cl). 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 KATHODE: A MODE 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 neutralised 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 unelect rifled 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 litmus 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 7 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 KATHODE ANODE 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 Cl. 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 naevi, 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 PO 4 ions ; in the + latter, more Na ions and Cl and CO 3 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 follows. 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 io 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 off (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 n 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 all 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 application of electricity. A patient suffers from headache as the result of low blood pressure. The application of the static breeze induces an erythema 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 will frequently relieve pain in the region of muscles and fasciae e.g. the lumbar 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 will 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 rhythmic 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 indirectly, 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 16 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, 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 line 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- sired, and the periods FIG. 5. Plan of commutator of Leduc. of flow and of in- When the current flows from 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 the shortest. When the movable brush-holder is in Leduc's Mechanical the position CD', the period of current- Current Interrupter. f es \ s the shortest and of n - flow the The essential part of the apparatus is a disc of insulating material mounted on the axle of a small motor and rotating with ^ (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 FIG. 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 8 F C C' \ A 4 D' B FIG. 7. RuhmkorflPs 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 f , 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 of 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 will 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 B 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 y^h second ; from A to C ^^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 dynamo. 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-called "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. n. 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 B to A 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. n. Plan of Ewing's Rhythmic Reverser much in the way used with an alternating current dynamo." F ARABIC 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 "shown 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 " Mcl~e " of the Primary 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 -Induct ion) in the opposite direction, impeding it and slowing its rate of rise to its maximum. This is shown in Fig. 13, a to b. 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. A i " 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 current, 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, b 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 ABCD -Induced current in. secondary coil AB- Make Current BCD -Break Current odbc - Exciting current in primary coil ab - Make Current be - Break Current 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, current m secondary coil AB - Make Current BCD -Break Current 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 ( T oVo 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 will 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. 1 6. 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 c 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, H 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 the. 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 will be described later, in the chapters dealing with these forms of electrical application. 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 100, 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 supplied, and the frequency of Current Patient 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 supplied 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 application 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 FIG. 18. 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 witn 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. 18) 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 slider, 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 FlG> 19< _ shunt Resistance towards A, the vol- 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 slider 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 milliampe re-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 milliampere 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- plied 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 dynamo 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 applied 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 off 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 sliding 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 100 ; 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 applied 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 \et 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 1 ) or in series (R 2 ). 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 static 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 part of the board. FIG. 24. Transformer for Light and Cautery ;, ,. 7 The alternating 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, D 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 poweruil 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 application to patients. Rectifiers are of two kinds chemical and mechanical. Chemical rectifiers depend for their action on the peculiar 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 Fioor or Pt ground cable (insi/la.te