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.
