Practical pathology

For practical diagnostic work or for pathologic research various instruments and utensils are necessary, although the expense of fitting up a working pathologic laboratory is not as great as it is often thought to be. The most expensive item, as well as the most important, is the microscope. This should be of the best make, and should be carefully selected and tested before the final purchase. As a rule the German makes, Zeiss, Leitz, and others, are to be preferred to the American instruments, in spite of the higher cost due to the duty imposed. I have found the German microscopes uniformly good and standing the wear and tear of a teaching laboratory much better than the American-made stands. I have never seen a poor Zeiss or Leitz objective, but cannot say the same thing of other makes. On the other hand, I have seen some American objectives that were as good as any German ones, but there are not many such. If one is going to buy an American microscope it should be bought on the same principle that one would buy a violin or a piano, wholly on its individual merits; and these can be ascertained only by having the instrument carefully examined and tested by an expert. Most laboratory workers will agree that the Zeiss instruments are the best; they are also the most expensive. For all practical purposes a Leitz stand costing ninety to one hundred dollars is quite good enough. A medium-sized continental stand, with rack and pinion and micrometer screw for coarse and fine adjustment, a triple nose-piece with dust-protector, Abbé condenser, iris diaphragm, plane and concave mirrors, three objectives (low, high and ¹/₁₂ oil-immersion), and two eye-pieces, a low and a high, form a complete outfit that answers all practical requirements. The new type of stand with curved arm and large stage, permitting the examination of all parts of a Petri dish or glass plate, and with the mechanism of the fine adjustment protected from any strain when the instrument is lifted by the arm is especially recommended. I have also found the black-finish very practical. The entire outfit need not be purchased at once; the stand with its accessories and a low power may first be purchased, and the higher-power objectives obtained later. One of the first luxuries is a movable adjustable stage. A very good and relatively cheap one is made by the Spencer Lens Co., of Buffalo. If a Zeiss stand is purchased the objectives A, D, and ¹/₁₂ oil-immersion, and oculars 2 and 4 best meet the requirements. Of the Zeiss apochromatic series, the objectives 16.0, 8.0, 4.0, and oil-immersion 2.0 mm., apert. 1.30, and oculars 4, 6 and 8 are most serviceable. The apochromatic objectives and the compensation-oculars are expensive, and need not be used for ordinary work, but are indispensable for photographic work. The Leitz objectives, 3, 6, or 7, and ¹/₁₂ oil-immersion, with oculars 2 and 4, and the equivalent objectives of the Spencer Lens Co. or Bausch and Lomb will answer all ordinary needs. For the purpose of microscopic measurements an ocular micrometer is necessary. This may be obtained as a separate eye-piece, or as a round piece of glass with measured divisions marked upon it that may be put into an ocular. The value of the scale must be determined for every lens and tube-length by estimating the number of its parts covering one part of a stage-micrometer marked in hundredths of a millimetre.

An instrument of any one of the above-mentioned makes, carefully selected and tested, should last its owner a life-time if proper care is taken of it. It should receive the same careful attention accorded a good violin or piano. It should be protected from dust, action of chemicals, heat, sunlight, and rough usage. When carried it should be supported in such a way that its weight is not thrown upon the thread of the adjusting screws. The adjustment, draw-tube and iris diaphragm should be carefully oiled at intervals, using the least possible amount of the best microtome oil. It is not necessary here to enter into the construction and theory of the microscope, as this knowledge has usually been obtained before the pathologic laboratory is reached. Experience has shown me, however, that it is always necessary to remind students, even those experienced for some time in the use of the microscope, of certain fundamental principles in the adaptation of microscopic technique to pathologic work. The following rules are of value:—

1. Use a low-power objective for all work except for the study of bacteria, microparasites and finer cell-structures. The aim should be to obtain as much of a bird’s-eye view of the “geography” of the section as possible. Contrast plays a very important part in pathologic diagnosis; and it is lost in high-power work, so far as the relations of cells and tissue-elements and pathologic products are concerned. The student almost invariably enters the pathologic laboratory with a fixed “high-power habit,” and he is usually greatly surprised to learn how much he misses with the high-power and how much he can see with the low-power. A motto used many years in my laboratory, “Low-power objective and high-power cortex,” is of greater educational value than may appear at first sight. A slide should be examined first with the naked-eye, as it is held against a window or light; then it should be examined under the low power. Rarely will it be necessary to use a high-power except for the purposes mentioned above.

2. Weak eye-pieces should be used; strong ones darken the field and tire the eyes. Only in the case of apochromatic lenses and compensation oculars can the strong ones be used without darkening the field too much.

3. In the use of higher powers see that the tube is drawn out to the proper length, as indicated in the directions sent with the instrument.

4. For pathologic work an Abbé condenser is essential. It should be pushed up to its proper position beneath the stage, and the plane mirror should be used with it, reflecting the light from a cloud if possible. Daylight is always the best light. When this cannot be obtained an incandescent or Welsbach lamp with ground-glass globe can be used. The concave mirror should then be used. The yellowish tint of artificial light may be avoided by the use of a piece of blue glass placed beneath the condenser, or a vessel of copper sulphate solution may be interposed. Especial lamps designed to meet the requirements are offered by the trade.

5. The iris-diaphragm should be adjusted by the same hand that moves the slide, usually the left one. With unstained preparations the diaphragm should be nearly closed; when using the oil-immersion it should be fully opened, as is also the case when stained preparations are studied with the lower power. With higher magnification the aperture is diminished somewhat, although color-effects are best shown with open diaphragm. In the study of pigments the diaphragm should be fully closed for a few moments to see if the pigment shows any color by reflected light. It is then examined by open diaphragm. In the study of sections the mirror and diaphragm should be manipulated in various ways to bring out all of the detail of the preparation, and should be adjusted to suit each preparation.

6. Objectives must never be screwed down until they strike the slide or stage. The higher-powers are frequently ruined in this way. When running the objective down always examine from the side to see that there is no danger of its striking the stage. In the use of the oil-immersion place the drop of oil upon the slide or cover-glass, and lower the objective by turning the coarse adjustment until the oil spreads out between the lens and the glass; then focus with the fine adjustment until a well-defined field is obtained. The oil-immersion lens should not be allowed to stand many consecutive hours in the oil. The oil should be cleaned from the lens by wiping the latter with lens-paper or a soft cloth; if the lens is sticky the paper or cloth may be moistened with benzol. The lens itself should never be wet with benzol, xylol, alcohol or any cleaning-fluid, because of the danger of softening the balsam in which the lenses are imbedded.

7. Use the mechanical stage only for differential blood-counting, or when the entire section is to be gone over carefully, or when certain details are found with difficulty and it is desirable to mark them for future reference. An immense amount of time is lost in the use of the mechanical stage for ordinary work. By moving the slide with the fingers of the left hand resting upon the stage an entire section may be gone over in a few seconds without missing any part of it; to accomplish the same thing with the mechanical stage requires much more time.

It is an excellent plan for the student to purchase his microscope when entering the medical school and to use his own instrument throughout his course. It is the one instrument without which no physician can afford to enter practice; and the student who uses his own microscope before graduation will continue to use it afterward. The microscope obtained, the remaining expenditure necessary for the fitting-up of a practical working laboratory of clinical and pathologic diagnosis need not be very great if one’s financial condition does not warrant spending with a free hand. It is possible with a little labor and ingenuity to make at home, or to show the local tinsmith how to make, a large part of the necessary apparatus, such as sterilizers, paraffin-ovens, drying ovens, thermo-regulators, etc., at a slight cost. Students of mine have made these things out of old tin cans and glass tubing; one student at a cost of less than three dollars constructed a microtome on which practical working sections could be cut. For the celloidin method no apparatus except the microtome is necessary, as the process of imbedding is carried on in bottles or dishes. These points are mentioned to offset the prevalent idea that a large expenditure is a necessity in installing a practical working laboratory.

In a large diagnostic laboratory, or in one intended for teaching and investigation, there are numerous accessories necessary to modern microscopic technique. For the observation of living objects a warm stage is needed. The simple electrical apparatus devised by Ross is the most convenient form, as it can be slipped on and off the slide without changing the focus. It can be attached to any electric light circuit and requires no attention.

For drawing from the microscope the improved form of the camera lucida, or the latest model of the Edinger drawing-apparatus are recommended. Both of these instruments have recently been greatly improved. The Zeiss microphotographic apparatus is by far the best for microphotographic work. For the polarization-microscope, microspectroscope, and the complicated and expensive ultra-violet and dark-field apparatus the worker is referred to the Zeiss catalogues. A simple and practical dark-field method for the illumination of bacteria, spirochætes and ultramicroscopic particles suspended in fluids requires only a strong illumination and the use of a Zeiss, Leitz, or Reichert dark-field condenser; or the very simple “India-ink” method may be used for the demonstration of spirochætes. (See Staining of Spirochætes.) Especial instruments for easily finding a certain field are obtainable, and are of great convenience in marking slides for photographic purposes.

Next to the microscope the most important instrument in pathologic work is the microtome. One that can be used for either celloidin or paraffin work, and that can also be utilized as a freezing microtome, should be selected in private work, when economy is desired. The majority can be used for either paraffin or celloidin, and one of the Becker models can be easily attached to the carbonic acid holder for the cutting of frozen material. The Bardeen freezing microtome is relatively inexpensive, very satisfactory, and can be easily attached to the carbonic acid tanks. It can be recommended for freezing work. The “slide” type, either that in which the knife-holder is moved by the hand directly or by a crank turned by the hand, is advised for ordinary diagnostic work. For students and beginners the crank is of great advantage, as the knife is securely held and cannot jump. The best microtomes are made by Schanze of Leipzig, Jung of Heidelberg, Becker of Göttingen, the Cambridge Scientific Co., the International Instrument Co., and the Bausch & Lomb Co. For either celloidin or paraffin work the medium or large Schanze slide-microtome or the Minot’s precision microtome are recommended; for cutting serial sections in paraffin the latest modification of the Minot automatic rotary microtome is especially adapted. The best microtome knives are made by Walb of Heidelberg. A long, heavy knife is to be preferred to a light one. For the freezing microtome a knife of the type of the blade of a carpenter’s plane set in a wooden handle should be used, Hones and strops of the best quality are necessary.

Paraffin-ovens and drying-ovens of suitable size, and constructed preferably of copper, are necessary for paraffin work. The water-space about the oven should be sufficiently large, and the temperature should be controlled by a thermo-regulator. Various models are offered in the trade, but they can be made more cheaply by the local tinsmith. The thermo-regulator can also be home-made by anyone who has the necessary training in glass-blowing usually given in courses in bacteriology.