The practical application of the Röntgen rays in therapeutics and diagnosis

Front matter

THE LIBRARY

OF

LOS ANGELES

Chapter II

General Properties of Tubes, 29 — Definition, 29 — Penetration, 30 — Production and Dissipation of Heat in Tubes, 31 — Operation of the Tube, 33 — Temperature, 34 — Clamping the Tube, 34 — Connecting Wires, 34— Punctures, 37— Testing the Tube, 38— The Choice of an X-ray Tube, 43— Bi-anode Tube, 44— Penetrator Tube, 45— Tubes with Vacuum Regulators, 45 — Thomson Tube, 45 — Bario-vacuum Tube and Regulator, 46 — Sayer Tube, 46 — Miiller's Regulating Tube, 49 — Tubes with Osmosis Regulators, 50 — Hirschmann's Tube, 51— Water-cooled Tubes, 52— Tubes with Heavy Targets, 52 — Double-focus Tubes, 54 — Tubes for Therapeutic Uses, 55.

Chapter III. Induction Coils, Interrupters, And Their Manage- Ment 60

Induction Coil, 60 — Winding of the Primary, 60 — Insulation between the Primary and Secondary, 61 — Insulation of the Secondary Winding, 62 — Insulation of the Secondary Terminals, 63 — Breakdown in Coils, 63 — Requirements of an Induction Coil for X-ray Work, 64 — Interrupters, 65 — Vibrating Interrupters, 67 — Rotary Interrupters, 70 — Mercury Interrupters. 73 — Turbine Interrupters, "5 — Electrolytic Interrupters, 78— Condensers, 85 — -Rheostats, 86 — Switches, 87 — Fuses, 87 — Meters, 88 — Induction Coil Installations, 90 — Portable X-ray Apparatus, 93.

CHAPTER IV. Size of Machine, 103 — Hard-rubber and Mica Plates, 104 — Regu

8 CONTEXTS.

PAGE lating the Discharge, 104 — Enclosing Case for Static Machine, 106 — Ozone and Nitrogen Oxids, 106 — Disturbing Effects of Moisture, 107— Oiling the Machine, 107— Series Spark (lap, 108— Polarity, 108.

Chapter V

Limitations of Fluoroscopic Examinations, 109 — Apparatus for Fluoroscopy, 109 — Series Spark Gap, 110 — Fluoroscopes and Fluorescent Screens, 112 — Adjustable Diaphragms, 116 — Guarding against Over-exposure, 116 — Screens for Preventing Burns, 117 — Importance of Proper Relation of Fluoroscope, Tube, and Patient, 117 — Fluoroscopic Examinations of Head, Face, and Neck, 117 — Shoulder, 118 — Extremities, 118 — Thorax, 119 — Abdomen and Pelvis, 121 — Location of Foreign Bodies with the Fluoroscope, 121 — Shenton's Method, 122 — Stereo-fluoroscopy, 124.

Chapter VI

Exciting Apparatus, 128 — Duration of Exposure, 131 — Distance of Tube from Plate, 132 — -Clothing, 132 — Radiographing Botli Sides for Comparison, 132 — Bandages, Splints, Plaster Casts, etc., 133 — Diagnosis of Malignant Growths, 133 — Marking the Skin, 133 — Tubes for Radiographic Work, 133 — Definition, 134 — Secondary Rays, 134— Degree of Penetration, 134— Tube-holders, 135— Tables, 138 — Envelopes and Plate-holders, 141 — Intensifying Screens, 143 — Prevention of Movement during Exposure, 144 — Importance of Correct Pose, 146 — Examining the Negative. 140 — Illuminating Device, 146 — Marking the Negatives. 148 — Record Book, 150 — Preserving the Negatives, 156 — Upper Extremity, 157 — Elbow, 158 —Arm, 160— Shoulder-joint, 160— Scapula, 162— Clavicle, 162- Foot, 165— Medio-tarsal joint, 165— Ankle, 165— Leg, 166— Knee-joint, 16Q— Thigh, 170— Hip-joint, 170— Head, Face, Neck, 171— Face, 173— Teeth, 173— Neck, 174— Thorax, 174— Position of the Patient, 175 — Esophagus, 176 — Spinal Column, 176 — Lumbar Vertebrse, 176 — Abdomen and Pelvis, 177 — Stones in the Bladder, 178 — Stones in the Kidneys and Upper Part of Ureters, 178 — Gall-stones, 180 — Localization, 183 — Stereoscopic Radiographs, 190 — Interpretation of the Negative, 194.

Chapter VII. The Photographic Materials And Their Manipula- Tion 195

Plates, 195— Size of Plates, 197— Keeping the Plates, 197— Developers, 197— Developing the Plates, 200— Fixing Baths, 201— The Dark Room, 202— Rubber Gloves, 204— Printing, 204.

Chapter VIII. The Choice Of An X-ray Outfit 208

Apparatus for, 210 — Volt Direct Current, 209 — For Alternating-

CONTEXTS. 9

PAGE

current Circuits, 211 — When no Lighting or Power Circuit is Available, 213 — Selection of Tubes, 214 — Accessory Appliances, 215.

Chapter I

Gross Effects upon Tissues, 221 — Pigmentation, 222 — Dermatitis, 223 — After-effects on the Skin, 225 — Burns Involving the Subcutaneous Tissue, 225 — Extent of Burns. Pain. Scars, 226 — Chronic X-ray Dermatitis, 229 — Hyperkeratosis, 229 — Changes in the Appendages of the Skin, 230 — Deep-seated X-ray Effects, 231 — Time of First Appearance of Symptoms, 234 — Duration of X-ray Burns, 236— Relapses, 238— Cumulative Effects, 239— Idiosyncrasies, 239 — Question of Dangerous and Safe Exposures, 241 — Influence of Various Factors on Susceptibility, 245 — Immunity, 245 — Anodyne Effect of X-rays, 246.

Chapter II. The Histological Changes Produced In Tissues By

X-RAYS 249

Alopecia in Guinea-pigs, 250 — Epidermis, 250 — Hair and Sebaceous Follicles, 251 — Cutis, 251 — Microscopic Changes in Psoriasis under X-rays, 259 — Microscopic Changes in Lupous Tissue, 260 — Lepra, 263 — Changes in Carcinomatous Tissue under X-rays, 263.

Chapter III. The Effect Of X-rays On Bacteria 27s

The Effect of X-rays on Bacteria in Cultures, 278 — Effect of X-rays on Bacteria in Living Tissues, 283.

Chapter IV. The Causes Of The Phenomena Observed In Tissues

AFTER EXPOSURE TO X-RAYS 286

What is the Active Agent in the Production of the Tissue Changes Following X-ray Exposures? 286 — What is the Property in X-rays that Affects Tissues? 292.

Chapter V. The Technique Of X-ray Exposures For Therapeutic

PURPOSES 302

Kienbock's Technique, 302— Scholtz's Technique, 305— Oudin's Recommendations, 306 — Williams' Technique, 306 — Beck's Technique, 307— Schiff and Freund's Technique, 308— Factors Affecting the Quality of X-rays, 308 — Standard Light, 309 — Influence of Amperage and Voltage, 310 — Quality of Tubes, 310 — Duration

10 CONTENTS.

PAGE

and Distance, 311 — Frequency of Exposure, 311— Preliminary Exposures to Determine Susceptibility, 311 — Distance of Tube, 311 — Record of Exposures, 312 — Necessary Apparatus, 312 — How far should X-ray Effects be Carried? 314 — Apparatus, 317 — Coils vs. Static Machines, 317 — Coils, 319 — Source of Energy, 319 — Meters, 319— Interrupters, 320— Tube-holders, 320— Tubes, 321— Protectives, 325 — Masks for Special Parts of the Body, 327 — Aluminum Screens, 329 — Insulation of Patient, 330.

Chapter X. Tuberculosis And Similar Diseases 371

Lupus Vulgaris, 371 — Tuberculous Ulcers and Scrofuloderma, 390 — Tuberculous Vesical Fistula, 393 — Tuberculosis of Glands, 393 — Tuberculosis of Larynx, 395 — Tuberculosis of Joints, 395 — Tuberculosis of Genito-urinary Tract, 396 — Abdominal Tuberculosis, 396 — Pulmonary Tuberculosis, 397 — Syphilis, 398 — Leprosy, 399 — Actinomycosis, 399 — Blastomycosis, 399.

CHAPTER XL CUTANEOUS CARCINOMA 403

Chapter XII

Carcinoma of the Breast, 468 — Recurrent Carcinoma of the Breast, 470 — Summary, 492 — Primary Carcinoma of the Breast, 493 — Summary, 497 — Mediastinal Tumors, 499 — Carcinoma of the Esophagus, 500.

Chapter XIII

Deep-seated Carcinoma of the Head and Neck, 502 — Carcinoma of Neck, 502 — Conclusions, 505 — Carcinoma of Mouth and Pharynx,

CONTENTS. 11

PAGE

506 — Dee]) Carcinoma in the Orbit, 507 — Carcinoma in the Abdomen, 509 — Carcinoma in the Pelvis, 510 — Carcinoma of the Anus and Rectum, 513.

Chapter XIV. Sarcoma And Other Granulomata 514

Sarcoma, 514 — Sarcoma of Parotid, 523 — Sarcoma of the Eye, 530 — Mycosis Fungoides, 531 — Granuloma of Uncertain Character, 531.

Chapter XV. The Prophylactic Use Of X-rays After Operations

FOR MALIGNANT DISEASES 53<S

The Use of X-rays Preliminary to Operation, 541.

Chapter XVI. Pseudo-leukemia, And Various Other Affections . . 542

Pseudo-leukemia, 542 — Leukemia, 552 — Neuralgias, 556 — Rheumatism, 557 — Pruritus, 557 — Goitre, 558 — Scars, 558 — Elephantiasis, 560 — Callous Sinuses, 560 — Chronic Ulcers, 560 — Naevus, 560 — Vascular Nsevi, 565 — Verruca, 566 — Clavus, 566 — Senile Verruca, 566— Leucoma, 566.

Chapter XVII

Non-malignant Diseases, 567 — Malignant Diseases, 568 — Prophylactic Use of X-rays, 570 — Use of X-rays Preliminary to Operations, 570— Permanency of Results, 570 — Length of Treatment of Successful Cases, 571 — Reasons for Different Results in Similar Cases, 571 — Effect of X-ray Exposures on General Health, 572 — Effects on the Blood, 573 — Danger of Metastasis Under X-ray Exposures, 574 — Use of Other Treatment in Conjunction with X-rays, 575

INDEX 577

PART I.

X-RAY APPARATUS AND ITS USE IN DIAGNOSIS.

BY

E. W. CALDWELL.

Preface To Part I

IN the seven years that have elapsed since the discovery of the x-ray very little has been added to our knowledge of the pure science of the subject beyond what is set forth in Rontgen's classical papers.

The art of applying these rays in medicine and surgery has steadily advanced, and valuable improvements in methods and appliances have been made by many enthusiastic workers in every part of the civilized world.

In the pages that follow I have not attempted to describe all the valuable work that has been done with the x-ray in diagnosis, but to present in a brief but fairly comprehensive way the methods and the various forms of apparatus with which the best results have been achieved. I have given special attention to many of the details which make up a good practical technique, and have devoted considerable space to the discussion of x-ray apparatus and the methods of using it.

There is a tendency among medical men either to underestimate the value of the x-ray as an aid to diagnosis or to fail to appreciate its limitations. I have therefore tried to show in a conservative way just \vbat may and what may not be accomplished with it in the present state of the art.

Among those who are actively engaged in x-ray work there is a great diversity of opinion as to what type of apparatus and what methods of procedure are best. These varying opinions result largely from the fact that excellent work has been done with almost every known type of apparatus. I have tried to discuss impartially the merits of the (Afferent appliances employed in x-ray work, and to show what types are best suited for the different kinds of work and the various conditions of current-supply. In doing this one must necessarily make statements which are more or less dogmatic, and in which the

16 PREFACE.

''personal equation'' is an important factor. I have not hesitated to express my convictions freely, although some of them are not in accord with commonly accepted views.

The indications which the x-ray gives of pathologic conditions of the thoracic region is a large subject by itself, and has been ably discussed by many writers who are familiar with its medical aspects. I have therefore felt unable to do more than refer to their work and to tell how the examinations are made.

The discussion of the elementary principles of electricity and the description of simple electrical apparatus — batteries, electromagnets, etc. — are for a similar reason omitted from these pages.

In preparing this work I have gathered ideas from most of the existing books on the subject, and have contributed such of my own original work as seems to have an established practical value.

I am indebted to Dr. J. Mackenzie Davidson, Dr. AY. Y. Cowl, Dr. Grunmach, Dr. E. AY. Shenton, Dr. F. H. Williams, Dr. A. B. Johnson, and others eminent in .r-ray work for courtesies extended to me in connection with their various developments of the art. To the founders of the Edward X. Gibbs -Y-ray Laboratory I am indebted for rare opportunities for observation and experiment in this fascinating field.

E. W. CALDWKLL.

Introduction

PROBABLY the first x-rays were produced by Crookes in his experiments on electrical discharges through vacuum tubes in 1875. He did not recognize the x-ray, and for twenty years following these experiments it remained unnoticed, and almost unsuspected.

In 1893 and 1894 both Herbert C. Jackson, of King's College, London, and Professor Lenard came very near making the great discovery. It remained, however, for Professor Wm. C. Rontgen, of Wiirzburg, to bring these rays from their hiding-place and give us some clue to their nature.

The study of the history of electrical discharges in rarefied air and gases leads us far back toward the beginning of the nineteenth century, but it was not until 1858-1859 that Geissler made the first vacuum tubes. These tubes were of comparatively low vacuum (about 0.0025 mm.), and the electrical discharge through them produced a delicate glow, sometimes striated, and varying much in form and color with the degree of exhaustion and the composition of the rarefied gases they contained.

Professor Hittorf about 1860 discovered that the luminous stream of discharge in a Geissler tube could be deflected by a magnet — a fact which has an important bearing upon the subsequent experiments of Crookes, Hertz, Lenard, and Rontgen.

The work of Geissler and Hittorf was followed several years later by the experiments of Crookes with discharge tubes of much higher vacuum (about 0.000001 mm.). With these high vacuum tubes Crookes discovered new phenomena. He found that with sufficiently high vacuum the luminous glow within the tube disappeared, and demonstrated that within

2 17

18 INTRODUCTION.

it there was a rectilinear radiation from the cathode which was a projection of particles of highly attenuated gas at exceedingly high velocity. He called this radiation cathode rays, and on account of the peculiar behavior of gas in this exceedingly rarefied state he conceived it to be as different from gas in its properties as ordinary air or gas differs from a liquid. He spoke of this highly attenuated condition as the fourth or radiant state of matter. He found that cathode rays were intercepted by metallic plates within the vacuum tube, that their impact against the glass wall of the tube produced in it a greenish phosphorescence and fluorescence and an increase in temperature. He concentrated these rays at the focus of a concave cathode, and by this means was able to produce brilliant fluorescence and a very high temperature both at the walls of the tube and in various substances within it. He also noted that the cathode rays were deflected by a magnet.

In 1892 Hertz announced that the cathode rays would penetrate gold leaf and other thin sheets of metal, within the tube. Soon afterward Hertz died, and his experiments were continued by his assistant, Lenard, who found that many of the phenomena of the cathode rays could be observed outside of the Crookes tube. He experimented with a vacuum tube closed at the end opposite the cathode with a thin sheet of aluminum, and found that the radiation which proceeded through or from the aluminum wall of the tube would pass through many substances opaque to ordinary light ; after passing through such substances it would excite fluorescence in crystals of barium platino-cyanid and many other salts, and that it would affect sensitive photographic plates in much the same manner as ordinary light.

Lenard thought that all of these phenomena were due to the cathode rays alone, and, although it can scarcely be doubted that not only in his experiments but in those of Crookes, Hertz, and other investigators, x-rays were produced, they were not recognized, and it remained for another discoverer to bring the results of these long years of patient scientific research into practical application in our daily life.

Early in November, 1895, Professor William Conrad Ront-

INTRODUCTION. 19

gen, then Professor of Physics at the Royal University of Wiirzburg, noticed that a piece of paper coated with barium platino-cyanid fluoresced brilliantly in the neighborhood of a Crookes tube, even when the tube was covered with cardboard which intercepted all of the ordinary light. Further investigation proved that the fluorescence was caused by a radiation which emanated from the point of impact of the cathode ray against the glass wall of the vacuum tube. It was evident that this radiation did not produce the sensation of light, and that it passed readily through cardboard, which was opaque to ordinary light. Rontgen also noticed that all substances were transparent to this radiation, although in widely different degrees, varying roughly with the density of the material; that the radiation was rectilinear; that it could not be refracted or reflected to any appreciable extent, and that it was not deflected by a magnet. Hence it was obvious to him that this radiation was different from the cathode rays of Crookes, Hertz, and Lenard. He continued his observation both with the fluorescent screen and the photographic plate. Most of his early work was of a purely scientific nature, and had for its object to determine, if possible, the exact nature of the new radiation, which he named x-rays, probably because of the significance of the letter x in the mathematical formulae.

Using photographic plates wrapped in black paper to protect them from ordinary light, Rontgen obtained with the x-ray shadow pictures of metallic objects in a wooden box and of the bones of the hand. The great possibilities of the x-ray in surgery were noted by him, and in December, 1895, he communicated his discovery to the Physico-Medical Society of Wiirzburg. This communication was published immediately all over the civilized world, and hundreds of investigators repeated the experiments of Rontgen and took up at once the work of practical development of his discovery.

The use of the x-ray in the diagnosis of fractures, location of foreign bodies, etc., at once became general, and in the first few months following its discovery experiments were made to determine its effect upon pathogenic micro-organisms in culture tubes. These experiments gave negative results, but

20 INTRODUCTION.

a little later a number of investigators observed valuable therapeutic effects when the rays were directed upon living tissues affected with tubercular or malignant disease.

The generally accepted theory of the x-ray is that it is a disturbance of the ether, somewhat of the nature of ordinary light, but differing from it in being a series of isolated impulses instead of a regular wave phenomenon. Although we do not know just what the x-ray is, the same thing may be said of gravitation and many other physical phenomena more familiar to us. For the purpose of the physician and surgeon it is quite sufficient to know how to produce and control the rays, but it may be well to remember that they originate within a Crookes tube at the point of impact of the cathode stream against a solid body; that they travel in straight lines; that they cannot be refracted or reflected as ordinary light; that, therefore, we can only obtain shadow pictures from them; that their range in quality is much longer than the range of the whole visible spectrum, and that the successful use of them depends upon the skill in those manipulations which secure for us the quality and intensity of the ray needed to accomplish the desired results.

Rontgen's first experiments were made with the familiar pear-shaped tube in which the source of the x-ray is spread over a comparatively large surface. Probably the most useful single contribution that has been made to the practical side of the subject is the suggestion of Mr. Herbert Jackson of using the focus tube of Crookes, thus reducing the source of the x-rays to a comparatively small area, enabling the production of sharp shadows, and making it possible to use a much stronger exciting current.

Chapter I. The Essentials Of An X-ray Equipment

THE two essentials of an x-ray equipment are Crookes tubes, and apparatus capable of delivering electrical energy at sufficiently- high potential to produce discharges through them.

In addition to the Crookes tubes and exciting apparatus an x-ray outfit comprises a vast number of auxiliary devices, such as tube-holders, switchboards, controlling mechanism for coils and static machines, plate-holders, fluoroscopes, operating tables, localizers, etc., which will be described in detail elsewhere.

The modifications of the Crookes tube which are used in practical x-ray work are made in many forms and fitted with many auxiliary devices. They consist essentially of sealed glass bulbs, containing two or three electrodes, and exhausted to a very high vacuum. One of the electrodes is made of aluminum, shaped like a concave mirror, and called the cathode because it is connected with the negative terminal of the exciting apparatus. Near the focus of this negative reflector is an electrode, which is usually a flat disc of platinum, connected with a terminal wire extending through the glass bulb. This electrode is commonly connected with the positive wire from the exciting apparatus, and is sometimes called the anode. However, the essential point about it is that it receives the impact of the cathode stream, and becomes the source of the x-rays. It has, therefore, been called the target or anti-cathode, and it may or may not be the anode of the tube. The various forms of tubes and methods of connecting them and regulating their vacua are described in detail in the next chapter.

For exciting Crookes tubes an electrical discharge of rather high potential is necessary. The potential required will vary with the resistance of the tube, but will always be much higher

22 ESSENTIALS OF AX X-RAY EQUIPMENT.

than can be obtained directly from batteries or electric lighting circuits, and will in practical work be more than 100,000 volts. By comparison it may be said that the E. M. F. of an ordinary storage cell is about 2 volts, the incandescent lighting circuits are usually about 110 or 120 volts, the current used for operating trolley cars is about 500 volts, and in long distance power transmission alternating currents at 25,000 to 60,000 volts have been used.

Electrical discharges suitable for operating Crookes tubes may be obtained with a static machine, high-frequency coil, or from the ordinary induction coil. Excellent results have been obtained with all these appliances, and each has its peculiar advantages.

Influence Machines. — The influence machine, or static machine as it is commonly called, is an apparatus which converts mechanical energy directly into electricity at suitable potential for use with x-ray tubes. It consists essentially of a number of discs of glass or mica arranged to revolve in an enclosed case. An electrical charge is produced upon the surface of the revolving plates, collected from them by toothed collecting combs, and led out through the side of the case to suitable terminals. These machines are described more in detail in Chapter IV.

Induction Coils. — The induction coil is an electro-magnetic apparatus which transforms the energy of the ordinary electrical current derived from a batten', or electric lighting circuit, into discharges of suitable potential for exciting the Crookes tube. It consists essentially of a core of magnetic material, a primary winding consisting of a few turns of coarse copper wire through which the primary or exciting current flows, and a secondary winding of a great many turns of very fine wire in which a high potential secondary discharge is generated. The core is made of a bundle of fine soft iron wires, or strips of sheet-iron laid up in the form of a cylinder from 1^ to 3 inches in diameter, and from 1£ to 7 feet long. Upon this core the primary winding is wound in from 1 to 4 layers. Sometimes the ends of the different layers are brought out to separate terminals so that they may be connected together in various combinations. Outside of the primary winding and very carefully

INDUCTION COILS. 23

insulated from it, usually by a thick hard-rubber tube, is the secondary winding of very fine wire about the size of a small sewing thread. The difference of potential in the different parts of this secondary winding is very great, and it is therefore necessary that great precaution be taken to secure thorough insulation of the various parts during its manufacture. In practice the secondary winding is usually imbedded in a mass of insulating wax. The ends of this secondary winding are provided with well-insulated terminals from which lead wires are carried to the Crookes tube.

The action of an induction coil is briefly as follows: An electrical current from a battery, or other sources, is passed through the primary winding, causing the core to become magnetic. Thus, a certain amount of the energy of the exciting current is stored up in the core. When the primary current is interrupted, the core very suddenly loses its magnetism and the energy stored up in it reappears as an electrical discharge of very short duration and very high potential in the secondary winding. In practical x-ray work this magnetization and demagnetization of the core are made to take place very rapidly — from 5 to 200 times a second. This is accomplished by various devices for rapidly starting and stopping the current through the primary winding of the coil. Such devices are known as interrupters. They have been made in many forms; some of the best-known types are described in Chapter III.

The degree of magnetization of the core increases at a comparatively slow rate, but its demagnetization is very sudden at the break of the primary circuit. The secondary discharge produced therefore at the opening of the primary circuit is of exceedingly short duration, probably not more than onefive-hundredth part of a second. In a coil operating at 50 interruptions a second there would be in one second 50 secondary discharges of exceedingly short duration followed by intervals of rest about ten or twenty times as long as the periods of the discharge. Thus it will be seen that there is a difference between the discharge obtained from an induction coil and that from a static machine, which when connected directly to the Crookes tube yields practically an even steady flow of current, much

24 ESSENTIALS OF AN X-RAY EQUIPMENT.

weaker but occupying the whole period. However, Crookes tubes excited either with a static machine or coil produce practically the same effects upon the photographic plate, upon the tissues of the body, and, so far as the eye is concerned, upon the fluorescent screen.

High-frequency Coils. — The high-frequency coils of Tesla, Kinraide, and others operate in a somewhat similar manner to the ordinary induction coil, but they are excited not by an ordinary electric current interrupted suddenly a few times a second, but by a series of very rapidly oscillating currents of perhaps several hundred thousand , alternations a second. Owing to the exceeding rapidhy of the oscillations of the primary current, these high-frequency coils can be made to give high-potential discharges with a comparatively small number of turns of fine wire in the secondary winding. They produce brilliant x-ray effects, but they give discharges which alternate in direction, and which are, therefore, not so well adapted for practical x-ray work as those obtained from a static machine or ordinary induction coil. The alternations of the discharge cause much wear on the Crookes tubes, and they produce sources of x-rays at other points than the target, thus impairing the definition of the tube. For radiographic purposes, therefore, the high-frequency outfits are not very satisfactory, though for therapeutic work they answer very well, except for the rapid destruction of the tubes.

Available Sources of Electrical Energy. — The electrical energy necessary for operating x-ray apparatus may be obtained either from batteries or electric lighting or power circuits.

Batteries. — All forms of batteries are objectionable, because of the corrosive solutions they contain, because they deteriorate more or less rapidly, and because of the annoyance and trouble due to the corrosion of contacts, breakage, etc.

An electrical battery consists essentially of two electrodes of dissimilar materials immersed in a conducting solution of such a nature that chemical changes take place when the two electrodes are so connected that an electrical current may flow from one to the other. The energy of the current produced is derived from these chemical changes. In nearly all

STORAGE BATTERIES. 25

primary batteries one of the electrodes is composed of zinc, and during the action of the battery this zinc electrode, or element, enters into chemical combination with the solution, and is worn away in proportion to the amount of current passed through it. It is therefore necessary after a time to renew both the zinc and the solution. On account of this troublesome and expensive process primary batteries are not recommended when other sources of electrical current are available.

There are several forms of primary batteries on the market which will deliver strong enough currents for operating induction coils. Of these may be mentioned the bichromate cell, having a voltage of 1.8, the Edison-Lalande with a voltage of 0.7, and the Gordon-Burnham with a voltage of about 1.5 a cell.

Storage Batteries. — In the storage battery the two dissimilar electrodes consist of two dissimilar oxids of lead which are held upon plates of metallic lead which serve as conducting supports for them. These are immersed in a solution of dilute sulphuric acid. In a storage battery the chemical changes which go on during the passage of the current are such that the original condition of the electrodes or elements may be restored by forcing a current through the cell in an opposite direction. It is therefore a much simpler matter to recharge a storage battery than a primary battery, because the elements do not have to be disturbed or renewed.

Lead storage batteries have an E. M. F. of about 2 volts and, since from 6 to 20 volts are required to operate an induction coil, from 3 to 10 storage cells will be needed. Some arrangement must be provided for charging these cells. They may be transported to a charging station, or if they are to be used for only a few minutes at a time at intervals of two to three days they may be charged by a primary battery, which does not deliver its energy fast enough for operating a coil directly, but which will store up in a day or two in a storage battery sufficient energy for operating a coil for a few minutes. The most suitable form of battery for this purpose is the ordinary gravity cell, which has been used extensively for telegraph work. These gravity cells will remain

26 ESSENTIALS OF AX X-RAY EQUIPMENT.

in operation for several months on one charge, and may be connected permanently with the storage battery. About 3 or 4 cells of the gravity battery will be required for each storage cell. When a storage battery is allowed to remain discharged for some time, abnormal chemical processes go on, which seriously impair its usefulness. They should, therefore, not be allowed to become fully discharged, and should be kept as nearly as possible fully charged all the time.