Medical microscopy : a guide to the use of the microscope in medical practice

Front matter

MEDICAL & STANDARD BOOK CO ,

Baltimore, "_J^

Boston

Preface

Within recent years the microscope has gradually been brought more and more into use as an aid to diagnosis. In certain classes of diseases, notably those of the chest and urinary organs, it has become almost a routine practice, in hospitals at any rate, to examine the sputa and deposits, and the use of the microscope is rapidly being extended to private practice.

In this work an effort has been made to lay before practitioners and students the most simple methods of preparing microscopic sections, and of the examination of urinary deposits, sputa, blood, etc. At the same time, for those who wish to extend their studies further, more elaborate methods have been detailed, and chapters added on the examination of food and bacteriological methods. It would have been beyond the scope of the book to have given descriptions of all the pathological changes found in the different organs, but a chapter on "Tumors" has been inserted, as for purposes of diagnosis, such examinations are frequently made in the operating theatre or post-mortem room.

Many of the illustrations are original, but I have also to thank Profs. Ziegler, von Jaksch, and Crookshank, Drs. Troup, Parkes, and Crocker, for permission to use many of their figures.

I have also to thank Prof. Stirling, Drs. Vincent Harrjs and Sims Woodhead, for allowing me to copy

vii

Vlll PREFACE.

many formulas from their works, and especially Dr. Wynter for consenting to my making use of the material collected for our joint work on " Clinical and Practical Pathology." Also my thanks are due to Mr. Mansell Moullin, Mr. Eve, Dr. A. Garrod, and Dr. Herman, for their kind advice and help, also to Mr. Lewis for his aid in the matter of illustrations, and to the various firms who have provided clients of apparatus.

Queen Anne Street.

CHAPTER I. The Microscope and Accessories

PAGE

Choice of an Instrument — Compound Microscope — Requisites of a good microscope : stage, diaphragm — Qualities of a good objective : defining power, flatness of field, penetrating power, angle of aperture, resolving power — Nose-piece — Oculars — Camera-lucida — Makers of microscopes — Use of the microscope — Abbe's Condenser — Microscope lamp — Drawing objects — Micrometer — Accessory apparatus — Cathcart's microtome— Swift's microtome — Williams' freezing microtome — Reichert's microtome — Rocking microtome — Valentin's knife — Glass slides — Cover-glasses — Normal saline solution — Iodine in iodide of potassium (Gram's solution), 9

CHAPTER II. Hardening and Decalcifying

General remarks — Choice of hardening fluid — Absolute alcohol — Methylated spirit — Midler's fluid — Bichromate of potash — Chromic acid — Chromic acid and spirit — Ammonium chromate — Bichromate of ammonia — Corrosive sublimate — Platinum chloride — Osmic acid — Picric acid — Decalcifying fluids — Nitric acid — Perenzi's solution — Hydrochloric acid — Von Ebner's solution — Picric acid, 42

CHAPTER III. Embedding

General remarks — Freezing media — Gum — Dextrin — Simple embedding— Infiltration methods — Embedding in celloidin : and in paraffin, 55

IX

X CONTENTS.

CHAPTER IV. Cutting Sections

PAGE

General remarks — Cutting with Cath cart's microtome — Cutting with Swift's microtome — Use of Williams' ice freezing microtome— Cutting sections embedded in celloidin — Cutting with Reichert's microtome — Collodionization of sections — Cutting sections in paraffin — Cutting in series — Cutting with rocking microtome, 62

CHAPTER V. Staining

General Remarks — Choice of a stain — Staining with hematoxylin arid eosin — Staining with carmine and picric acid — Lithium carmine — Acidulated alcohol — Picro-carmine — Alum-carmine — Ammonium carmine — Borax carmine — Staining in bulk — Safranin — Iodine green — General stains : Bismarck brown, rubin, orseille — Multiple staining — Treble staining, .... 74

CHAPTER VI. Selective Stains

General remarks — Metallic stains : nitrate of silver, chloride of gold, osmic acid — Staining micro-organism: methylene blue, Loffler's method, Kiihne's method, Mast-zellen, Gram's method, Weigert's modification of Gram's method, Neelsen- Ziehl method — Methods of staining actinomyces : amyloid reaction, karyokinetic figures, , . 92

CHAPTER ATI.

Clearing and Mounting.

Fluid media : glycerine, glycerine jelly, glycerine mounting fluid, Farrant's solution, iodine mounting fluid — Cementing materials— Mounting in solidifying media — Clearing agents : Canada balsam, dammar varnish — Breaking down old specimens, HO

CONTENTS. XI

Examination of Fresh Tissues.

Normal saline solution — Serous fluid — Iodized serum — Teasing —

Softening — Landois' fluid, . 139

CHAPTER XII. Preparation of Individual Tissues and Organs

Epithelium — Areolar tissue — White fibrous tissue — Elastic tissue — Adenoid tissue — Adipose tissue — Gelatinous or embryonal tissue — Cartilage — Bone — Teeth — Muscle — Nervous system — Circulating system — Glandular tissue — The eye — Internal ear — Digestive system — Lungs — Thyroid gland — Liver, spleen, etc. — Genito-urinary system, 144

CHAPTER XIII. The Examination of Tumors

Fibromata — Myxomata — Enchondromata — Osteomata — Myofibromata — Sarcomata — Papillomata — Adenomata — Epitheliomata — Carcinomata, 153

Xll CONTENTS.

CHAPTER XIV. Examination of Urinary Deposits

PAGE

Method of examination — Organized deposits : epithelium, red blood corpuscles, leucocytes, mucus, fat, casts, spermatozoa, fragments of morbid growth — Pathogenic micro-organisms : tubercle bacilli, erysipelas — Septic micro-organisms — Sarcinae, bilharzia haematobia, filaria sanguinis hominis, eustrongylus gigas, echinococci — Non-pathogenic micro-organisms — Unorganized deposits — Sediments occurring in acid urine : uric acid, amorphous urates, urate of soda, oxalate of lime, sulphate of lime, cystin, xanthin, tyrosin, leucin, hippuric acid, haematoidin and bilirubin, soaps of lime and magnesia — Sediments occurring in alkaline urine : triple phosphates, neutral phosphate of lime, basic magnesium phosphate, amorphous phosphate of lime, carbonate of lime, urate of ammonia, cholesterin, indigo — Gravel and calculi — Extraneous matters — Preservation of urinary deposits, „ 167

CHAPTER XV. Examination of the Faeces

Method of examination — Macroscopic examination — Foreign bodies — Mucus and fibrinous shreds — Portions of bowel separated from intussusceptions — Intestinal concretions — Gall-stones — Microscopical examination : food matters, crystals, red blood corpuscles, leucocytes, epithelium — Vegetable parasites : bacillus of tubercle, bacillus of typhoid fever, bacillus of cholera, bacillus of cholera nostras — Non-pathogenic organisms— Animal parasites : amoeba coli, infusoria — Taenia mediocanellata — Taenia solium — Taenia nana — Bothriocephalus latus — Distoma hepaticum — Distoma lanceolatum — Distoma sinense — Ascaris lumbricoides — Ascaris mistax — Oxyuris vermicularis — Tricocephalus dispar — Anchylostoma duodenale — Strongylus gigas — Anguillula intestinalis — Trichina spiralis, 21 1

CONTENTS. Xlll

CHAPTER XVI. Examination of Sputum

PAGE

Method of examination : quantity, consistence, color, odor, bronchial casts — Microscopical examination : leucocytes and mucus corpuscles, compound granule cells, red blood cells, epithelium, elastic tissue, Curschmann's spirals, tonsillar casts, corpora amylacea, portions of membrane, crystals, Charcot -Leyden crystals, concretions, foreign bodies, accidental ingredients, . 248

CHAPTER XVII. The Micro-organisms of Sputum

Tubercle bacilli: Neelsen-Ziehl method, Ehrlich's method, Gabbett's method, Gibbes' method — Pneumococci — Actinomyces — Micrococcus tetragonus — Septic micro-organisms — Fungi — Infusoria — Entozoa, 28]

CHAPTER XVIII. Examination of Vomit

Method of examination — Food matters — Epithelium — Red blood

cells — Leucocytes — Sarcinse — Yeasts — Micro-organisms, . . 295

CHAPTER XIX. Examination of Discharges and Contents of Cavities

Serous exudations — Hemorrhagic exudations — Chylous exudations— Sero-purulent exudations — Putrid exudations — Purulent exudations : micro-organisms — Tubercle bacilli — Actinomyces — Bacillus of leprosy — Bacillus of anthrax - — Bacillus of syphilis — Gonococcus — Bacillus of Glanders — Trichina spiralis — Cysticercus cellulosae — Hydatid cysts — Ovarian cysts — Dermoid cysts — Hydro -nephrosis — Spermatocele, 299

I

XIV CONTENTS.

CHAPTER XX. Discharges from the Genital Organs

PAGE

Discharges from the male genital organs : seminal fluid, spermatic stains — Discharges from the female genital organs : vaginal secretion, Trichomonas vaginalis — Membranes : mucus, fibrinous clots, vaginal casts, membranous dysmenorrhcea, membranes of early abortion, ..312

CHAPTER XXI. Examination of the Blood

Red corpuscles — White corpuscles — Blood plates — Counting the corpuscles — Gowers' haemocytometer, Thoma-Zeiss haemocytometer — Estimation of the amount of haemoglobin in the blood: Gowers' baemoglobinometer, v. Fleischl's haemometer — Olygocythaemia — Polycythaemia — Leucocythaemia — Leucocytosis — Microcythaemia — Poikilocytosis — Melanasmia — Vegetable parasites : bacillus of anthrax, tubercle, typhoid fever, glanders and tetanus, spirillum of relapsing fever, haematozoa of malaria — Animal parasites ■ Filaria sanguinis hominis, Bilharzie haematobia — Examination of blood stains, 32]

Chapter XXII

Vegetable parasites : Tricophyton tonsurans, Microsporon furfur, Achorion Schonleinii — Animal parasites : pediculi, Sarcoptes hominis, Acarus folliculorum, 348

CHAPTER XXIII. Examination of Food and Water

Wheat — Barley — Rye — Oatmeal — Maize — Rice — Beans — Peas — Sago — Tapioca — Arrowroot — Potato — Turmeric — Bread — Flour — Tea — Coffee — Cocoa — Examination of drinking water, 354

CONTENTS. XV

CHAPTER XXIV. Bacteriological Methods. page

General Considerations — Apparatus required : steam-sterilizer, hot-air sterilizer, hot-water filter, incubator, accessories — Cultivating media — Solid media: potato cultivations, nutrient gelatine, nutrient agar-agar, glycerine agar-agar, sterilized blood serum — Liquid media : bouillon, liquid blood serum, Pasteur's fluid, Cohn's fluid — Mode of using the solid nutrient media : test-tube cultivations, plate cultivations — Mode of using the liquid media : drop cultures — Examination of micro-organisms : cover-glass preparations, cover-glass impressions — Experiments on animals, 369

LIST OF ILLUSTRATIONS.

FIG. PAGE

1. Diagram of Optical Principle of the Microscope, io

2. Baker's New Student's Microscope, 13

3. Beck's Pathological Microscope, 15

4. Swift's Bacteriological Microscope, 17

5. Nose-piece, 18

6. Bausch and Lamb's Universal Microscope, 21

7. Abbe Chromatic Condenser, 24

8. Microscopic Lamp, 26

9. Prismatic Camera-lucida, 28

10. Abbe's Camera-lucida, 28

11. Eye-piece Micrometer, 29

12. Frazer's Modification of Cathcart's Microtome, 32

13. Clamp of Cathcart's Microtome, 33

14. Williams' Ether Microtome (" Swift's Microtome"), . ... 34

15. Williams' Ice and Salt Microtome, 35

16. Reichert's Microtome, 37

17. Rocking Microtome, . . „ 38

18. Valentin's Knife, 39

19. Diagram for Embedding Box, 57

20. Cells from a Periosteal Myxoma of the Thigh, 155

21. Section from an Osteoid Chondroma of the Humerus, ... 156

22. Section Through the Margin of a Sarcoma Affecting the

Intermuscular Connective Tissue, . . 158

23. Section from a Giant -celled Sarcoma, showing also Spindle-

shaped Cells, 159

24. Fibro-adenoma of Mamma, 162

25. Section from an Epithelioma of Skin, 164

26. Carcinoma of the Mamma, 165

27. Vaginal Epithelium, 170

xvii

XV111 LIST OF ILLUSTRATIONS.

FIG. PAGE

28. Epithelium from the Bladder, Ureter, and Pelvis of the Kidney, 171

29. Renal Epithelium, Healthy and Fatty, 172

30. Blood Corpuscles in Urine, 173

31. Pus-Cells in Urine Affected by Acetic Acid and Unaltered, 177

32. Urinary Casts, 183

33. Spermatozoa, 188

34. Uric Acid, . 199

35. Amorphous Urates, 201

36. Urate of Soda, 202

37. Oxalate of Lime, 203

41. Triple Phosphates, 210

42. Stellar Phosphates, 211

43. Cholesterin, 214

44. Head of Taenia Mediocanellata, 238

45. Head of Taenia Solium, 240

46. Ova of Intestinal Parasites, 244

47. Trichocephalus Dispar, 246

48. Bronchial Stolon, 256

49. Various Cells in Sputum, 261

50. Elastic Tissue, 265

51. Elastic Tissue Partially Encrusted with Lime Salts, .... 268

52. Curschmann's Spirals, 269

53. Cast of a Tonsillar Crypt, 271

54. Charcot- Ley den Crystals, 274

55. Silk Fibres, 278

56. Cotton Fibres, 278

57. Linen Fibres, 279

58. Wool Fibres, . 279

59. Bacterium Pneumonia Crouposa, 289

60. Oidium Albicans, 292

62. Trichina Spiralis in Muscle, 307

63. Head of Cysticercus Cellulosse, 307

64. Hydatids, 309

65. Wall of Hydatid Cyst, 310

LIST OF ILLUSTRATIONS. XIX

FIG. PAGE

66. Normal Semen, 313

67. Trichomonas Vaginalis, 317

68. Gower's Haemocytometer, 323

69. Pipette (Thoma-Zeiss Haemocytometer), 326

70. Counting Slide (Thoma-Zeiss Apparatus), 327

71. Cross-section of Thoma-Zeiss Apparatus, 327

72. Counting Scale (Thoma-Zeiss Apparatus), 328

73. Gower's Haemoglobinometer, 331

74. Von Fleischl's Haemometer, 332

75. Poildlocytosis, 339

76. Filaria Sanguinis Hominis, 343

77. Bilharzia Haematobia, 346

78. Tricophyton Tonsurans, 349

79. Achorion Schonleinii, 351

80. Wheat-starch Grains, 355

81. Barley-starch Grains, 356

82. Oatmeal-starch Grains, 357

8^. Maize-starch Grains, 358

84. Rice-starch Grains, 358

85. Bean-starch Grains, , 359

86. Pea-starch Grains, 359

87. Sago-starch Grains, 360

88. Tapioca-starch Grains, 360

89. Arrowroot-starch Grains, 361

90. Potato-starch Grains, 361

91. Acarus Farinas, 363

92. Coffee, Cells of Testa and Cellular Structure, 365

93. Chicory, Dotted Ducts and Cellular Structure, 365

94. Cocoa-starch Cells, 366

95. Koch's Steam Sterilizer, 371

96. Hot-water Filtering Apparatus with Ring Burner, .... 372

97. Babes' Incubator, 374

98. Platinum Needles, Straight, Hooked, Looped, 375

99. Method of Inoculating a Test-tube Containing Sterile Nutri-

ent Jelly, 383

100. Method of Inoculating Test-tubes in the Preparation of

Plate Cultivations, 385

101. Damp Chamber for Plate Cultivations, 387

Chapter I. The Microscope And Accessories

The first question that naturally arises when preparing to study the use of the microscope in medicine is as to the choice of an instrument. The number of different forms of microscopes now in the market is legion, and it is an exceedingly difficult matter to make a selection of any particular one. In order to do so, an intimate knowledge of its structure and mode of working is necessary, and it is very advisable that an inexperienced person, instead of choosing for himself, should seek the advice of a more expert friend to help him in his search, for nothing is more annoying, after expending a large sum on a large, showy stand, than to find that for practical scientific work it is almost useless.

Before stating in detail the requisites of a good microscope, it will be well to give a short description of the instrument as sold by all modern makers.

Microscopes are distinguished as simple or compound. In the former, the rays which enter the eye of the observer come from an object brought near to it after refraction through either a simple lens, or a combination of lenses acting as a simple lens, its action as a " magnifier" depending on its enabling the eye to form a 2 9

IO MEDICAL MICROSCOPY.

distinct image of the object at a much shorter distance than would otherwise be possible.

The "compound microscope" consists of at least two lenses, so placed relatively to the object, to the eye, and to one another, that an enlarged image of the object, formed by the lens placed nearest to it (the "object-glass"), is looked at through the lens nearest the eye (the "eye-piece"), which acts as a simple microscope in magnifying it ; so that the compound microscope may be described as a simple microscope applied to look at an

Fig

i.

B i

b&Ajc

-^hi

hx

Diagram of Optical Principle of the Microscope.

enlarged image of the object, instead of at the object itself.

This description of the compound microscope will be made clearer by referenc to the above diagram (Fig. i).

a b is the object placed in front of the object-glass Z. An inverted and somewhat magnified image, a'b' ', is formed on the opposite side of the glass. P is the eye-piece. Now the distance between the two lenses, L and P, is such that the position of the image a'b' is between the eye-piece and its focus. From this it follows that for the eye at E,

THE MICROSCOPE AND ACCESSORIES. II

looking through the eye-piece at the image, the same effect is produced as with a simple microscope, so that instead of the image a'b' , another image AB is seen, which is virtual. This second image is also inverted in reference to the object.

The lenses are set in a tube blackened internally, the eye-pieces fitting into the upper end, whilst the objectives are screwed on to the lower end. This tube, which can be lengthened to some extent telescopefashion, is supported on a firm metal "stand," consisting of two chief portions, the "column" and the "base."

The tube is capable of being raised or lowered without lateral deviation, this being accomplished by means of a telescopic joint, or a rack and pinion arrangement in the better class of instruments. These mechanical appliances are known as "adjustments." There are usually two such, the " coarse " and the " fine." The coarse adjustment has just been described ; the " fine adjustment " consists of a fine screw usually placed at the top of the column.

Projecting from the column is a horizontal plate, the " stage," for the reception of the object to be examined. It possesses a circular aperture for the passage of light, the amount of illumination being determined by "diaphragms" of different sizes. Below the stage is a swinging mirror capable of being moved in all directions, and having two surfaces, a plane and a concave. Inserted into the stage are two clips for fixing the glass slides in any desired position.

In microscopes intended for bacteriological work, a "sub-stage" is inserted between the mirror and the stage proper; this carries the "condenser" and its diaphragms, and by means of screws can be moved laterally, or upward and downward.

A second "condenser" is usually supplied for purposes of looking at opaque objects by reflected light ; this, however, is seldom, if ever, required for medical work, all the objects being transparent and examined by transmitted light obtained from below.

The column is connected with the base by means of a stiff hinge, so that the tube can be fixed either in a perpendicular or horizontal position, or at any angle.

What, then, are the requisites of a good microscope?

For useful practical work, it is desirable not to have too large an instrument. Especially should a binocular be avoided. It is cumbersome, the number of screws around the stage becomes bewildering, and no advantage is to be gained by it for medical work over a well-made monocular, with a simple sub-stage condenser.

Steadiness is essential. This is secured by a wide base. In nearly all microscopes the pedestal is either of the horse-shoe, or some modification of the tripod pattern ; it should be heavy enough to allow of both adjustments being turned, and of the object being freely moved on the stage without shaking the instrument.

The column must, of course, be perfectly rigid, and this property is secured by the use of good, stout metal.

Both adjustments should turn easily and regularly, especially the fine one, for if this be at all stiff, or if the thread be in the least irregular, great annoyance will be experienced.

The stage is usually three inches long by two and a half wide. It is not advisable to have a "movable" stage. By means of the fingers the glass slide can be moved more readily, and by practice quite as smoothly as by any mechanical contrivance, whilst extra screws and levers are apt to be in the way.

There should be plenty of room between the mirror and the stage, so as to allow the insertion of a condenser ; if sufficient space be not allowed the full effect of this con-

FlG. 2.

Baker's New Student's Microscope.

trivance is not experienced. It is most certainly desirable to have a condenser ; the search for micro-organisms has now become almost a matter of routine in certain cases of doubtful diagnosis, and for their sure detection a special illumination is absolutely necessary.

The diaphragm is made of several different patterns. The most ordinary form consists of a " wheel" of diaphragms of various sizes, and should be examined to see whether the apertures are concentric with the axis of the instrument. Another form consists of small blocks in which the openings are pierced, all fitting into a common receptacle, which is inserted below the stage. The most important feature is that the diaphragm must be placed i7nmediately beneath the object, in order to secure the best results.

There are several more complicated forms, such as the " iris," but for a description of them the reader is referred to larger treatises on microscopy.

Although the choice of a " stand " is of no mean importance, the chief point is of course the selection of the objectives.

For ordinary histological work, an "inch " lens and a " quarter-inch " is sufficient, but if it be intended to undertake the examination of sputum, etc., a twelfth-oil-immersion is necessary, as the micro-organisms cannot be seen with any certainty without this power.

According to the Continental systems, the first named lenses are represented by Nos. 3 and 7 of Hartnach, or A and D of Zeiss.

It should be borne in mind that the term " one-inch objective," etc., indicates only that such a lens should possess the same magnifying power as a single lens of one-inch focus, and that it does not refer to the distance which the front of the lens focuses from the object, this varying greatly with the different makers.

The qualities of a good objective are: — defining

THE MICROSCOPE AND ACCESSORIES.

*5 power, flatness of field, penetrating power, and resolving power.

Defining power. — Expressed in more exact language

Fig. 3.

Beck's Pathological Microscope.

this means that the objective has been properly corrected for spherical and chromatic aberration.

"Spherical aberration" causes the lines of the object to appear blurred and foggy, instead of being distinctly defined and clearly separated from one another. If the glass be not free from chromatic aberration, colored fringes appear around certain spots, blue, if the lens be under-corrected, red, if over-corrected. " Defining power" may be tested by examining a stage-micrometer and observing if each division can be clearly distinguished.

Flatness of field. — If an object be moved about from one portion of the field to another, it ought to appear equally well-defined in all parts. Thus, taking the stage-micrometer again as a test, the lines should be sharp and clear, and perfectly parallel to one another in every part of the field.

Penetrating power. — By this term is signified the power of an objective object to view several planes of an object without altering the focus. A section of liver is a good test for judging this properly.

The penetrating power of a lens is dependent on its " angle of aperture." This is the angle made by two lines drawn from opposite sides of the aperture of the object-glass with the principle focus of lens.

If the system of lenses has a " low angle," its penetrating power is greater than one which possesses a " high angle " of aperture.

In connection with this subject it may be mentioned that low-power objectives with a high-angle and consequent shorter working distance will define much better than those with smaller apertures.

Resolving power. — This again depends entirely upon the aperture, supposing the glass to be perfect in other respects; for good effects the angle ought to be large. Some authorities object to the term "resolving power" as being'synonymous with " defining power." An object-

Fig. 4.

Swift's Bacteriological Microscope.

ive, however, may have perfect defining power, and yet by reason of its want of aperture it will be unable to distinguish certain minutiae. It defines all that it can take up, but cannot define what is not imaged by it.

In choosing an objective, it is well to select one with an universal screw, so that it can be used with any stand, otherwise an " adapter " will become necessary.

A "nose-piece" (Fig. 5) carrying two or three objectives is a useful adjunct, saving a great deal of time when

Fig. 5.

Nose-piece.

working with more than one power. This little piece of apparatus should be tested to ensure of there being sufficient space for the oil-immersion to revolve between the tube and the stage, and some minute object should be selected by means of the low power and arranged so that it occupies the centre of the field ; the high power should then be turned round and lowered on to the glass, when this particular object should still be in the centre of the field ; if this be not the case, the nose-piece is not correctly "centred " and should be rejected.

Not more than two oculars, a high and low, will be required ; their function, as already stated, is to magnify the image formed by the objective; but enlargement is better obtained by drawing out the tube, or by substituting a stronger lens, than by using a high eye-piece, which is trying to the eyes.

A Camera-lucida is also of service for drawing the outline of specimens ; one need not be bought, however, for it is easy to manufacture one by bending a small piece of tin-foil round the upper end of the tube, and arranging it in such a fashion as to support a cover-glass at a proper angle to the eye-piece ; the angle is readily ascertained by experiment, and this simple contrivance has the advantage over the more complicated ones, in that the glass being so thin, only one image of the pencil instead of two is seen, and it is consequently much easier to use. This is the principle of Beale's " neutral tint reflector."

It would be invidious and beyond the function of this book to recommend any particular maker from whom a microscope should be bought. There are many excellent dealers both in London and the Provinces. It is presumed that those who make use of these directions will not be desirous of possessing a large and expensive instrument. Very good "students' microscopes" are now made by many of the London firms, which can be highly recommended. They are fitted with all the apparatus necessary for simple bacteriological work, and the cost is from £\(> to ^20.

Any of the following makers may be fully trusted to supply good instruments, and any omissions that occur do not imply that therefore other firms are not equally as reliable : —

C. Baker, 243 and 244 High Holborn.

Beck, 68 Cornhill.

Crouch, 66 Barbican.

Pillischer, 88 New Bond Street.

Parkes, 5 St. Mary's Row, Birmingham.

Ross, 164 New Bond Street.

In America very similar instruments, possessing everything that can be desired, and excellent both in manufacture and in the qualities of the lenses, may be obtained from Joseph Zentmayer, 209 South Eleventh Street, Philadelphia, and Bausch & Lamb Optical Company, 48 and 50 Maiden Lane, New York, and at 543 North St. Paul Street, Rochester, N. Y. These firms also supply all microscopical apparatus aryi accessories.

If a suitable stand be already to hand, the extra apparatus may, of course, be added. This applies more particularly to an oil-immersion lens and Abbe's condenser. The best immersions are perhaps those of Zeiss, but they are very expensive. A very good lens is made by Leitz, and costs about ^5, whilst a condenser can be fitted for about £1. Both the lens and condenser may be obtained from any of the makers above mentioned.

Having detailed the form of the microscope and the essentials of a good and practical one, we now pass to the use of the instrument. This may seem somewhat superfluous, but a few hints to the inexperienced may save them not only various petty annoyances, but probably also the loss of valuable lenses.

In removing the instrument from its box it should be grasped by the column, not by its foot, as thereby much strain on its bearings is prevented. Any jarring of the adjustments soon puts them out of order. For this reason when in constant use it is preferable to keep it under a bell-jar rather than to be constantly lifting it out of and into its case. Scrupulous cleanliness cannot be too strongly Fig. 6.

Bausch & Lamb's Universal Microscope.

insisted upon. Each time the lenses are used they should be carefully wiped with a soft piece of chamois leather. This applies more particularly to the oil-immersion lens, for if the oil be allowed to remain on any length of time it is apt to become hard, and great trouble is experienced in removing it.

It not infrequently happens when working with the high powers that these are accidentally forced through the cover-glasses and so become covered with balsam ; this is best removed by moistening the chamois leather with a little alcohol or xylol, rapidly passing it over the lens and immediately drying it. This must be done very cautiously, as the lenses are " set " in balsam, and there is some danger of this being dissolved by the spirit, and if such be the case, the damage is extremely difficult to rectify.

Having settled the microscope on a firm table or stand (for any vibration is very disturbing) and inclined it at an angle to suit the convenience of the observer, without causing him to adopt an uncomfortable or tiring posture, the mirror is turned so as to reflect the light up the tube. The best illumination is obtained with a North light, so as to avoid the direct glare of the sun, which is trying to the eyes ; a very good light is obtained by reflection from a white cloud. If a low power is being used the flat side of the mirror should be employed, and if a high one, the concave side.

In conjunction with the mirrors, various diaphragms are used to regulate the quantity of light passing to the specimen. In examining unstained sections, or objects such as are found in urinary deposits, the diaphragm with the smallest aperture that can illuminate the whole of the field is applied. With stained specimens no regulation of the amount of light is necessary.

With regard to the selection of a power to view any particular specimen, the rule is, never use a higher power than is absolutely necessary for clearly bringing out the minutiae of the object under examination. The inch lens should therefore first be used to gain a general idea of its structure and nature, and then the quarter-inch may be substituted ; for ordinary medical work a higher power will not often be needed, except for the examination of micro-organisms. In using the high powers, in order to avoid breaking the cover-glass by injudicious use of the coarse adjustment, it is a good plan before applying the eye to the tube to lower the lens until it just touches the cover-glass, and then to work it upward by means of the fine adjustment whilst looking down the microscope; if the structure be very fine, it is advisable to slightly move the slide up and down with the left hand, as a moving object is more easily caught sight of than one which is still.