Essentials of laboratory diagnosis designed for students and practitioners

Front matter

Glass.

Book ? ^

GopightN

Preface To Third Edition

This little work has been found so satisfactory by the general practitioner and undergraduate student that but slight changes other than the correction of a few typographical and grammatical errors were found necessary in preparing this edition for the press so soon after the publication of the second edition about one year ago.

The number of cuts has been increased, and a new full-page color plate of normal and pathologic blood-cells has also been added.

F. A. F.

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Preface To First Edition

A knowledge of so many branches of medicine is required of the medical student of to-day, and as the time at his command is comparatively limited, a manual embodying the essentials of the subject such as this aims to do cannot but prove useful. At the same time, it is believed to contain all information necessary to provide a working outline of clinical laboratory methods for the busy practitioner.

The book is not intended to take the place of the many excellent and exhaustive text-books on Clinical Medicine, but rather to supplement them, by pointing out to the busy student and practitioner simple and reliable methods by which he may obtain the information desired, without unnecessary expenditure of valuable time upon difficult, tedious or untried methods.

The author has endeavored in this work to present in as concise a manner as possible a selection of the analytical methods employed in the clinical laboratory, without burdening the reader with unnecessary detail, cumbersome methods, etc., many of which are extremely difficult, often requiring considerable knowledge of general chemistry and elaborate apparatus, which may place them beyond the reach of the practitioner.

For these reasons it is hoped that this little work will prove equally valuable to the student and the practicing physician.

In preparing this work special effort has been made to bring the subjects treated up to date, by the introduction of such new methods as have proven reliable. Some of the

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PREFACE. v

material is entirely new. and many of the plates and cuts have been prepared from original drawings and photographs by the author. Special mention is to be made of the plate and drawings (Plate VI, Figs. IT and 18) of the normal relations of the stomach, which were prepared expressly for this work by Dr. George E. Pfahler.

The appendix has been arranged to furnish a working basis for the equipment of a clinical laboratory, at the same time affording reference for the preparation of stains, reagents, etc., mentioned in the text.

The leading authorities have been freely consulted, and much material has been obtained from such authorities as v. Jaksch, Sahli, Caille, Grawitz, Krehl, Max Braun, Tyson, xlbbott, Purdy, Eemsen, and Holland.

The author takes this opportunity to express his appreciation of the many valuable suggestions received from Drs. Judson Daland and Wm. Egbert Bobertson, and Mr. Geo. B. Johnson, of the F. A. Davis Company; also, to his associate, Dr. Francis J. Dever, for invaluable aid in the preparation of the manuscript and in correcting the proof.

F. A. F.

1831 Chestnut Street, Philadelphia.

INTRODUCTORY NOTE.

By Judson Daland, M.D.

Professor of Clinical Medicine, Medico-Chirurgical College, Philadelphia.

This book should be in the possession of every medical student and most practicing physicians. It contains, as its title implies, the essentials, and only the essentials of those procedures necessary to clinical laboratory diagnosis. The peculiar value of this book resides in the concise and practical manner in which each subject is treated and each test described, and the entire absence of all superfluous data.

This book is particularly well suited, not only to the medical student in the preparation of cases assigned to him for study, but also to practicing physicians, who have grasped the necessity of establishing a small laboratory in connection with every-day work. Those possessing such a laboratory will find it necessary to consult this book at short intervals. The more it is employed the more will its practical value be demonstrated. I unhesitatingly recommend this work to medical students, and trust that it will find a place in the laboratory of every practicing physician.

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Contents

PAGE

Section I. The Microscope .' 1

Selection of the Instrument, 1. Care of the Microscope, 1. The Parts of the Microscope, 2. The Oil-Irnmersion Objective, 5. Apochromatid Objectives, 5. Illumination, 6. Cleaning' the Microscope, 7. The Mechanical Stage, 8. The Warm Stage, 9. The Maltwood Finder, 9. Examination of Urinary Sediments, 11. Examination of the Blood, 16. The Camera Lucida, 17.

Section II. The Sputum 19

General Considerations, 19. Gross Composition, 20. Color, 21. Reaction, 23. Air Content, 23. Odor, 24. Hemoptysis, 24. Macroscopic Examination, 25. Microscopic Examination, 26. Preparation of Stained Specimens, 29.

Section III. The Blood 31

Chemical Composition, 31. Methods of Obtaining Specimen, 31. Appearance of Fresh Blood, 32. Specific Gravity, 33. The Amount and Reaction, 34. Estimation of Per Cent, of Hemoglobin, 35. Estimation of Erythrocytes, 37. Hematokrit Determination of Erythrocytes, 39. Percentage of Erythrocytes, 40. The Color-Index, 41. The Volume-Index, 41. Estimation of Leukocytes, 42. Examination of Fresh Drop, 43. Staining Methods, 45. Hematologic Terms, 47. Varieties of Leukocytes, 48. Differential Count, 49. Leukocytosis, 50. The Anemias, 52. Chlorosis, 54. Leukemia, 54. Spectroscopic Examination, 56. Bacteriologic Examination, 58. Spirochete Pallida, 59.

Section IV. Opsonic Method 61

General Consideration, 61. The Theory, 61. Therapeutic Application, 63. Guides to Treatment, 63.

Section V. Blood-Pressure 65

Capillary Blood-Pressure, 65. Terms and Definitions, 65. Principle of the Sphygmomanometer, 67. Explanation of Readings, 69. The Sphygmomanometer, 69. Method of Using, 71. Systolic Reading, 72. Diastolic Reading, 72. Recording Observations, 74. Normal Blood- Pressure, 74. Variations in Blood-Pressure, 75. Alcohol and Tobacco, 78. Alimentary Hypertension, 79. Pathologic Pressures, 80. Valvular Disease, 81. Other Diseases, 86. In Life Insurance Examinations, 88.

Definition, 101. Classification, 102. Protozoa, 103. Platyhelminlhes, 107. Nematodes, 113.

Section IX. Determination of the Functions of the Stomach. 118

The Gastric Contents— Vomitus, 118. Methods of Obtaining Specimen, 119. Preliminary Preparation of the Patient, 120. Modified Ewald Test-Breakfast, 121. Technic of Removal of Test-Meal, 122. Inflation of the Stomach, 123. Determination of the Capacity of the Stomach, 125. Gastric Lavage, 126. The Acids of Digestion, 126. Estimation of Free Hydrochloric Acid, 129. The Organic Acids, 130. Test for Occult Bleeding, 131. Estimation of Peptic Activity, 132. Estimation of Trypsin, 136. Estimation of the Activity of Rennet, 136. Digestion of Starch and Sugar, 137. Determination of Gastric Activity, 137. Detection of Bile, 137. Test for Motor Functions, 137. Rontgen Ray Examinations, 138.

Section X. The Feces 143

Physical Characteristics, 143. Study of Intestinal Digestion, 144. Determination of Motor Functions of Gastro-Intestinal Tract, 146. Chemical Examination of Feces, 150. Occult Bleeding in Gastro-intestinal Tract, 153. Bacteria and Protozoa in Feces, 154. Clinical Significance of Examinations of Feces, 157. Foreign Bodies, Calculi and Concretions, 158.

Section XL The Urine 161

General Considerations, 161. Description and Importance of the Urine, 163. Physical Characteristics of the Urine, 164. The Amount, 166. The Specific Gravity, 168. Estimating the Total Solids, 171. The Reaction, 172. Chemical Composition of the Urine, 174. Phosphates, 176. The Sulphates, 179. The Chlorides 180. The Organic Constituents of the Urine, 181. Urea, 182. Uric Acid, 187. The Urates, 189. Creatinin, 191. Oxalates, 192. Abnormal Constituents of the Urine, 194. Albumin, 194. Glucose, 201. Cammidge Reaction, 209. Polarimetric Method, 210. Significance of Glycosuria, 210. Raw Sugars in Urine, 211. Acetonuria, 212. Diacetic Acid, 212. Oxybutyric Acid, 213. Bile Pigments. 215. Pyuria, 217. Epithelia in Urine, 218. Tube Casts, 218. Cylindroids, 221. The Inorganic Sediment, 223. Urinary Concretions, 225. The Diazo Reaction, 226. Drugs and Poisons in the Urine, 227.

Section XII. The Cerebro- Spinal Fluid 231

The Presence of Cerebrospinal Fluid, 231. Determination of the Cell- Content, 232. Determination of the Proteid-Content, 234. Interpretation of the Findings, 235.

Section XIII. The Body Fluids 236

Peritoneal Fluid, 236. Inflammatory Exudate, 236. Transudates, 236. Pleural Fluid, 237. General Considerations, 237. Non-Inflammatory Transudate, 237. Inflammatory Exudate, 237. Method of Making Permanent Stained Specimen, 237. Microscopic Appearance of Stained Specimens, 238. The Pericardial Fluid, 238. The Synovial Fluid, 238. Hydrocele Fluid, 239.

Section XIV. Human Milk 240

General Considerations, 240. Physical Characteristics and Composition, 240. Examination of Milk, 241. Determination of the Fat, 241. Determination of the Sugar, 243. Estimation of the Proteids, 243. Chemical Composition, 243.

CONTENTS. J x

PAGE

Section XV. Bacteriologic Methods 244

The Tubercle bacillus, 244. Differential Diagnosis, 246. Staining Methods, 246. Diplococcus Pneumonii, 248. Method of Staining Capsules, 249. Bacillus of Pfeiffer, 249. Bacillus Diphtheria?, 250. Gonococcus of Neisser, 251. Gram's Method of Staining, 252. Reaction of Bacteria to Gram's Method, 253. Loeffler's Method of Staining Flagella, 234. Sterilization, 255. Intermittent Sterilization, 259. The Autoclave, 261. Chemical Sterilization and Disinfection, 262. Preparation of Culture Media, 262. Nutrient Bouillon, 263. Nutrient Gelatin, 265. Nutrent Agar-Agar, 266. Glycerin Agar, 266. Blood- Serum, 267. Loeffler's Blood-Serum, 269. Technic for Plates and • Petri Dishes, 270. The Incubator, 271.

Section XVI. Serodiagnosis 274

Agglutination, 274. Widal Reaction, 274. Discussion of Complement Fixation, 276. Principle and Technic of the Wassermann Reaction, 278. Principle and Technic of the Noguchi Reaction, 280. Preparation of Reagents, 283. Standardization of Reagents, 286. Value of the Tests, 288.

Section XVII. Appendix , 290

Description of Laboratory Cabinet, 290. Urinalysis Test Set, 291. Report Forms, 293-298. Table of Clinical Terms, 299. Blood-pressure Chart, 300. Apparatus, 301. Chemicals and Reagents, 303. Stains, 308. Identification of the Tubercle Bacillus, 317. Antiformin Method, 318. Tubercle Bacilli in the Blood, 319. Tubercle Bacilli in the Feces, 322. Test for Pancreatic Activity, 322. Bile Pigment Reaction, 324. Leukocyte, Differential Count Computing Chart, 325. Modified Esbach Test, 326. Tables of Weights and Measures, 327-329. Comparison of Thermometers, 330.

Index 331

LIST OF ILLUSTRATIONS.

PAGE

Plate I. Author's Office Laboratory Frontispiece

Plate II. Normal and Pathological Blood-cells (Colored) 42

Plate III. Sphygmomanometer, in Position for Observation 80

Plate P7. Malarial Parasites. (Kolle & Wassermann) 96

Plate V. Intestinal Parasites of Man 104

Plate VI. Skiagraph. Normal Stomach. Child, Age 4 Years 140

Plate VII. Indican Scale. (Colored) 180

Plate VIII. Uric Acid Crystals with Amorphous Urates. (Peyer.) (Colored). 190

Plate IX. Calcium Oxalate Crystals and Phosphates 224

Plate X. Uric Acid Crystals, Cholesterin, Cystin, Tyrosin and Leucin 224

Plate XL Uric Acid Crystals 224

FIG.

1. American-make Microscope, showing Triple Nosepiece, etc 2

2. Mechanical Stage 8

3. Maltwood Finder 10

3 a . Camera Lucida 17

4. Bronchial Cast, from case of Fibrinous Bronchitis in service of Dr.

Judson Daland (Original) , 22

5. Fleischl Hemoglobinometer . . ., 32

6. Thoma-Zeiss Hemocytometer in case. (A. H. Thomas) 36

7. Appearance of Field of Thoma-Zeiss Hemocytometer, when properly

Mounted for Counting the Red Corpuscles 38

8. Daland Hematokrit. (A. H. Thomas) 39

9. Ruling of Chamber of Thoma-Zeiss Hemocytometer 42

10. Normal Pulse Tracing: Showing relation of Systolic, Diastolic, Pulse

Pressure, and Mean. Pulse pressure equals 30 QQ

11. Diagram of Relations of Armlet to Brachial Artery. Explanation of

Systolic Reading 67

ll a . Diagram of Relation of Armlet to Brachial Artery. Explanation of

Diastolic Reading 68

12. Sphygmomanometer 71

12 a . Diastolic Indicator 74

13. Wright's Coagulometer 91

14. Bogg's Coagulometer, diagrammatic representation 93

15. Outfit for Gastric Test-meal Removal, Lavage and Inflation 119

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x ji LIST OF ILLUSTRATIONS.

FIG. PAGE

16. Diagrammatic Representation of Arrangement of Bottle for Measuring

Cubic Contents of Stomach 125

17. Solid Line shows Form and Relation of typical normal Stomach, with

subject in standing posture 139

18. Dotted Line shows Form and Location of normal Stomach during filling.

Shaded portion shows Contraction and Change in form of Stomach 140

19. Strasburger Apparatus. (After Steele) 151

20. Various Forms of Urinometers and Urinometer Cylinders 169

21. Westphal Balance. (A. H. Thomas) 170

22. Various Forms of Ureameters 187

23. Urate of Soda and Crystals of Uric Acid, Oxalate of Lime, and Cystin . . 190

24. Esbach Albuminometer 199

25. Einhorn Saccharimeter during Performance of Test 207

26. Polarimeter. (A. H. Thomas) 210

27. "Large White Kidney." X 350. (Lenhartz) 219

28. Chronic Bright's Disease. X 350. (Lenhartz) 219

29. Sedimentation Glasses 220

30. Centrifuge Tubes 223

31. Arnold Steam Sterilizer. (A. H. Thomas) 260

32. Autoclave. (A. H. Thomas) 261

33. Thermostat or Incubator. (A. H. Thomas) 272

34. Portable Clinical Laboratory Set 292

35. New Graphic Chart for Recording Blood-pressure Observations 300

36. A Computing Chart to Facilitate Making a Differential Leukocyte

Estimation 325

THE MICROSCOPE.

SELECTION OF THE INSTRUMENT.

In purchasing a microscope one should consider nothing but the best. This is true economy, for a cheap or inferior instrument is always an unsatisfactory one which, when once bought, is hard to get rid of, and if later discarded for a better instrument, represents a total loss. The possession of a good microscope is an absolute essential. Its services are required in almost every investigation of modern clinical diagnosis, and there is hardly a chapter in this work which does not call for its use. While the finest and most expensive instruments are still of foreign make, there are, nevertheless, many of American make which compare favorably with the imported instruments. An example of a good American instrument is shown in Fig. 1, and is one of a series manufactured by the Bausch and Lomb Optical Co.

CARE OF THE MICROSCOPE.

In handling any instrument it is necessary to see that it is always grasped by some one of its solid parts — the base or the standard. Some of the newer makes are provided with an aperture in the standard for this very purpose.

If the instrument is to be in daily use it should be kept under a bell jar or in a specially prepared cabinet built above the work table. (See Frontispiece.) Eeference to Fig. 1 will illustrate the mechanism and the different parts with which one should become familiar before attempting to use the instrument. Efforts to use the microscope by any one unfamiliar with its different parts and adjustment should never be permitted, since careless handling may result in serious damage to the objective or other delicate parts.

DESCRIPTION OF THE MICROSCOPE.

Keferring to Fig. 1, the various parts of the instrument about to be described may be located.

The Ocular, or Eye-Piece, consists of one or more converging lenses, the combined action of which is to magnify the

COARSE ADJUSTMENT

OCULAR

DRAW TUBE

FINE ADJUSTMENT

HANDLE ARM

TUBE

TRIPLE NOSEPIECE WITH OB- JECTIVES

STAGE

IRIS DIAPHRAGM

SUBSTAGE CONDENSER

MIRROR

Fig. i.— American-make Microscope showing Triple Nosepiece and Aperture in Standard to facilitate handling.

image formed by the objective. This part is contained in a tube of its own, which telescopes into the top of the barrel, and is the part which the eye approaches when viewing the object.

DESCRIPTION OF THE MICROSCOPE. 3

Various oculars are usually provided, and are numbered from 1 to 8. As the number advances, the magnifying power of the ocular increases; at the same time the length of the tube decreases. It is advised, when increased magnification is desired, -to accomplish this by increasing the power of the objective rather than by using stronger oculars. The clearness and definition of the picture will then be preserved, whereas if the power of the ocular is increased it is usually at the expense of definition.

It will be found of great convenience to cement into one of the oculars a fine hair or eyelash. This should rest upon the upper surface of the central diaphragm of the ocular, when it will always be in focus. This serves as a pointer which can be used to single out from a blood or other specimen some special point of interest that it is desired to demonstrate to another person. This is particularly valuable in class demonstration.

The Barrel, or Tube, is the large tube of the microscope, w T hich serves as a conductor of the rays as they pass from the objective to the ocular.

The Objective consists of a system of converging lenses arranged at the lower end of the barrel, where it forms a magnified inverted image of the object. Upon this piece depends the magnifying power of the microscope. Most objectives are designated by numbers running from 1 to 15, these numbers representing the fractions of an inch at which the lens operates. Foreign makes are designated by letters which are not in any way directly comparable to the numbers of the American objectives. For one desiring three objectives, the most useful numbers will be found to be the 3, the 7 or 6, and the 12-oil-immersion, the 3 and 6 or 7 being chiefly employed in blood-counting, while the 12th is necessary for blood-examination and bacteriologic work.

The Stage is the table fastened below the barrel and in a right-angle plane to it. This serves to retain the object in a vertical plane to the optical axis of the instrument. The table is provided with spring clips to better hold the slide in position during examination. The newest Leitz scope is furnished with a movable (not mechanical) stage, which, by the operation of two milled screws, is capable of slight movement in all directions. This, when a mechanical stage is not at hand, is of great service in searching blood and bacteriologic slides.

The Reflector is a small mirror situated below the stage which serves to direct the rays of light upward through the object in the optical axis of the microscope. The reflector has two sides, one carrying a concave, and the other a plane, mirror.

The Sub-Stage Condenser (Abbe's) consists of a system of lenses arranged between the stage and the reflector. The object of this part of the instrument is to collect and condense the rays as they come from the reflector, so that they are focused upon the object, thus furnishing brilliant illumination.

The Iris Diaphragm is now universally employed for controlling the intensity of the illumination. This is held in the same carrier as the condenser, and is just below it. By means of a lever every gradation of light, from the most intense to absolute darkness, is readily obtained. The proper manipulation of this diaphragm constitutes a very important part of the practical knowledge gained from the use of the microscope, and has much to do with the success of many investigations.

The Adjustments. — The coarse adjustment is the rack-andpinion mechanism projecting from the upper part of the standard, and is employed to rapidly raise and lower the barrel and its attachments. The fine adjustment is a micrometer screw situated usually below the rack and pinion. This serves the purpose of very gradually raising or lowering the barrel in order to obtain exact focus.

The Draw-Tube is a very important adjunct of high-grade instruments, because by its skilful manipulation slight errors in refraction, due to inequalities in slide or cover-glass, may be corrected.

The Nose-Piece, or collar, is fastened to the lower end of the barrel, and permits the attachment of two or three objectives at one time in such a position that, by rotation of the collar, any one of them may be immediately brought into the axis of the instrument.

The most important accessories of the microscope are the objectives, and the quality of all microscope work largely depends upon their perfection. AYhile the quality of objectives vary much, one cannot go far astray if they are obtained through

APOCHROMATIC OBJECTIVES. 5

a reputable supply house or from a well-known manufacturer, such as the Zeiss or Leitz abroad, and the Bausch and Lomb Optical Co., IT. S. A.

THE OIL-IMMERSION OBJECTIVE.

The oil-immersion objective, or homogeneous system, is so constructed that when in use the pencil of light passing through the object to the objective traverses only media of the same refractive index. This is accomplished by placing between the cover-glass and the end of the objective a medium having the same refractive index as glass. To accomplish this a drop of cedar oil is placed upon the cover-glass, and the objective brought into contact with this, and the observation made through the oil. This class of lens is intended to work only with the oil, and is unsatisfactory when used dry. Frequently it is not convenient to use cedar oil for the preliminary examination often employed to determine the progress of staining, etc. ; here the staining fluid may be washed off and a drop of water used in place of the oil; this will give a sufficiently good picture for the purpose, and has the advantage of not interfering with the addition of further stain when desired.

The tube or barrel of the microscope is made in two forms, the long or English type being from 8 to 10 inches, and the short or Continental type having a length of G 1 /^ inches. The latter is the more desirable form, since the majority of manufacturers of objectives adjust them for the short tube.

APOCHROMATIC OBJECTIVES.

This term is applied to a particular variety of lens containing a special kind of glass (containing calcium fluoride), besides the usual crown and flint glass, the object of this being to produce a greater degree of achromatism, thus reducing chromatic aberration. The special value of these objectives when used with a compensating ocular (compensating eye-pieces are specially constructed for use with apochromatic objectives), is as follows : Three rays of the colored spectrum, instead of two, as in case of the achromatic glasses, are focused in the same plane, leaving only a minute tertiary spectrum; also with these objectives the spherical aberration is corrected for two colors in the brightest part of the spectrum, and the objective shows the same correction for marginal rays as for the central part of the aperture. Finally, apochromatic objectives admit the use of highly magnifying oculars. This form of objective is particularly useful in photomicrographic work, where it is very important to abolish chromatic aberration.

ILLUMINATION.

Illumination constitutes a most important factor in the practical use of the microscope, and upon its proper management depends very much of the efficiency of the work. Direct, unmodified sunlight is unsuited, and should not be employed, for general work. Noith light is the most uniform and steady, and is to be preferred. The use of artificial light should, as far as possible, be avoided, and when it must be used its character and color may be greatly improved by inserting a piece of blue glass between the reflector and the object. It is always necessary to keep the eye close to the ocular and if possible to keep the unemployed eye open. Too much light is always to be avoided, as it is only an added strain to the eyes, accomplishes nothing, and may materially interfere with the efficiency of the work.

Oblique Light. — For urinary work the oblique light is best. By this term is meant light in which the parallel rays from the plane mirror meet the optical axis of the microscope at an angle. This form of light may be obtained in the following ways: (a) By placing the reflector to one side of the stage; this results in an oblique ray without materially lessening the strength of the light; the condenser must, of course, be swung out of the w r ay. In microscopes which have a fixed mirror, i.e., only movable perpendicularly at right angles to the axis, oblique light may be obtained through the condenser, as follows: (b) First, focus the light upon the object through the condenser; then, lower the condenser until its focus is considerably below the plane of the object; thus the rays emerging from the condenser will decussate and then diverge, so that all but axial rays will fall upon the object in an oblique direction.

TO CLEAN THE MICROSCOPE. 7

TO CLEAN THE MICROSCOPE.

Should the lenses or oculars become blurred or spotted from dust or dirt, proceed as follows : If the dirt is upon the ocular it will be discovered by rotating the ocular within the barrel while observing the illuminated field of the microscope. If the obstruction is upon the ocular it will be seen to move; if upon the objective it will remain stationary during this manipulation. To find an obstruction upon the objective rotate it, when the spot or mark will move with it. Finally, if after testing both the objective and ocular in the manner described above the location of the dirt or dust is not demonstrated, the trouble will then be found upon the glasses or spectacles if the observer happens to wear them. Having located the trouble, remove the affected part and cleanse as follows : If careful polishing with bibulous paper or fat-free silk fails to accomplish the desired result, then moisten the silk or paper with a trace of distilled water, using this to aid in the removal, finally polishing dry. For oily or resinous smears a small amount of alcohol may be used. Special care should then be exercised to avoid any excess of the solvent which may enter between the individual lenses and, dissolving the cement, ruin the part. After using the oil-immersion it should always be cleaned before leaving the instrument. After removing the excess of oil with the silk, wipe off the remainder with a trace of xylol or benzine, immediately wiping dry. Cover-glass preparations may be treated in a similar way.

Glass surfaces should never be touched with the fingers, and great care should be exercised to avoid dropping and possible fracture of the oculars and objective. All metal parts of the instrument should be kept free from liquids, particularly acids and alkalies, benzine, xylol, alcohol, turpentine, and chloroform.

To clean the mechanical parts, none but the best machine oil should be used, and this only in small amounts and at long intervals. The polished brass requires nothing but occasionally polishing with clean chamois.

Two keynotes to successful use and preservation of the microscope are: handle with care and keep scrupulously clean.

THE MICROSCOPE.

THE MECHANICAL STAGE.

Of the many aids to exact work in the realm of clinical medicine the mechanical stage is of great practicability and wide application. Every possessor of a microscope should aspire to the possession of a mechanical stage, for this mechanism is not only a great time saver, but will materially aid in the search for bacteria and pathologic cells in the blood, and is practically a necessity in making a differential count.

Description. — Eeferring to Fig. 2, the general appearance of this instrument will be seen. It is designed for application to the stage of the microscope, upon which it is rigidly fastened

Fig. 2.— Mechanical Stage.

by a collar and set screw attached to the stand. It is important in this connection to note that most manufacturers of microscopes make a mechanical stage for their particular instrument, and which frequently is not interchangeable with microscopes of other manufacture, so that, before purchasing, one should be certain that the stage will fit the instrument for which it is intended. When attached to the stand the slide carrier should move in both directions without any undue force and without any irregularity or jarring of the mechanism, and to the limits of its movement should remain in close and even contact with the microscope stage.

The mechanical stage is fitted with two milled screws which are movable in either direction, and which convey gradual

THE MALTWOOD FINDER. 9

motion to the slide held in the jaws of the instrument. One of these screws controls the vertical, and the other the horizontal, motion, so that by proper manipulation it is possible to rapidly and accurately go over the whole of a specimen. (For more detailed description of the use of the mechanical stage in the differential count, see chapter on Blood.)

Most mechanical stages are provided with a millimeter scale and vernier reading to 0.1 of a millimeter, which serves not only to measure the size of small objects upon the stage, but is also very useful for locating objects of special interest upon any slide, so that they may again be found without difficulty. (See below the Maltwood finder and Pepper's application without the mechanical stage.)

THE WARM STAGE.

A further differentiation and improvement upon the mechanical stage is the stage prepared for preserving specimens at body-temperature during examination. This is provided with a thermometer which indicates the temperature of the object during examination. An extemporaneous warm stage has been described in another section (Blood Parasites) to which the reader is referred.

THE MALTWOOD FINDER.

In microscopic work, especially in studying blood or bacteriologic slides, some sort of "finder" is an essential part of the equipment. While the vernier scale, which is attached to most microscopes is fairly satisfactory for individual work, it does not fulfill all conditions demanded of it, since the same stage and microscope must always be used, and if by accident the relation between microscope and stage is altered ever so little, then all previous figures indicating location are rendered valueless.

The Maltwood finder (Fig. 3) does not possess the above disadvantages, and can be used universally with uniform results.

The Maltwood finder 1 consists of a heavy glass slide comparing exactly in size with the ordinary microscope slide. The central third of this slide is covered with a close network of

1 Wm. Pepper : Jour. Amer. Med. Assoc, July 20, 1908.

THE MICROSCOPE.

intersecting rectilinear lines which form a large number of uniform squares. Each square contains two figures arranged one above the other, so that no two squares represent the same combination (see below). This marking has been placed upon the slide by a photographic process.

1 1

1 2

2 2

1 3

2 3

1 4

2 4

All Maltwood finders are made interchangeable, the squares coinciding exactly in all slides.

Method of Using the Finder. — If on looking over the slide with the mechanical stage a part of the field is discovered which

Fig. 3.— Maltwood Finder, showing Dr. Pepper's Brass Angle Substitute for Mechanical Stage.

one desires to examine at a later time, the slide is carefully removed without altering the location of the mechanical stage and the Maltwood finder substituted; the square is then observed which corresponds with the center of the slide. This combination is to be jotted down, and then in order to make sure that the proper reading has been made, the finder and slide should be substituted for each other a number of times. Sup-