hundred lines of the ocular micrometer. Then calculate the value of each line of the ocular. This is done in the following manner: If the one hundred lines of the ocular cover seventy-five lines of the stage micrometer, then the one hundred lines of the ocular micrometer are equivalent to seventy-five one- hundredths, or three-fourths, of a millimeter. One line of the ocular micrometer will therefore be equivalent to one-hundredth Fig. 3i. — Micrometer £ye-P!eoe of seventy-five one-hundredths, or .0075 part of a millimeter, and as a micron is the unit for measuring microscopic objects, this being equivalent to one one-thousandth of a millimeter, the value of each line of the ocular will therefore be 7,5 microns. With the high-power objective in place, ascertain the value of each line of the ocular. If one hundred lines of the ocular cover only twelve lines of the stage micrometer, then the one hundred lines of the ocular are equivalent to twelve one-hun- dredths of a millimeter, the value of one line being equivalent to one one-hundredth of twelve one-hundredths, or twelve ten- thousandths of a millimeter, or .0012, or 1.2 u. It will therefore be seen that objects as small as a thousandth of a millimeter can be accurately measured by the ocular micrometer. Id making microscopic measurements it is only necessary to find how many lines of the ocular scale are covered by the object. The number of lines multiplied by the equivalent of each line will be the size of the object in microns, or mkro- mittimeters. <Callout type="important" title="Critical Rule">Always ensure the high-power objective is correctly calibrated before making measurements.</Callout> MICROMETER EYE-PIECES Micrometer eye-pieces (Figs. 23 and 24) may be used in making measurements. Thest- eye-pieces with micrometer com- J4. — Micronicler Eye-Piw binations are preferred by some workers, but the ocular microm- eter will meet the needs of the average worker. <Callout type="gear" title="Specific Equipment">Ocular micrometers and stage micrometers are essential tools for accurate measurements.</Callout> MECHANICAL STAGES Moving objects by hand is tiresome and unsatisfactory, first, because of the possibility of losing sight of the object under observation, and secondly, because the field cannot be covered so systematically as when a mechanical stage is used for moving slides. The mechanical stage (FiR. 25) is fastened to the stage by a screw. The slide is held by two damps. There is a rack and pinion for movmg the slide to left or right, and another rack a pinion for moving the slide forward and backward. CAMERA LDCIDA The camera lucida is an optical mechanical device fra aiding the worker in making drawings of microscopic objects. The instrument is particularly necessary in research work where it is desirable to reproduce an object in all its details. In fact, all reproductions illustrating original work should be made by means of the camera lucida or by microphotography. A great many different t>pes of camera lucidas or drawing apparatus are obtainable, varying from simple-inexpensive to complex-expensive forms. Figs. 26, 27, and 28 show ^mp| and complex forms. HISTOLOGY or MEDICINAL PLANTS MICROPHOTOGRAPHIC APPARATUS The microphotographic apparatus (Fig. 29), as the name implies, is an apparatus constructed in such a manner that it may be attached to a microscope when we desire to photograph microscopic objects. It consists of a metal base and a polished metal pillar for holding the bellows, slide holder, ground-glass observation plate, and eye-piece. In making photographs, the small end of the bellows is attached to the ocular of the micro- R scope, the locus adjusted, and the object or objects photo- I graphed. More uniform results are obtained in making such U. photographs if an artificial light of an unvarying candle-power is used. There are obtainable more elaborate microphotographic apparatus than the one figured and described, but for most workers this one will prove highly satisfactory. It is possible, by inclining the tube of the microscope, to make good micro- photographs with an ordinary plate camera. This is accom- plished by removing the lens of the camera and attaching the bellows to the ocular, focusing, and photographing. Fig. 29. — Microphotographic Apparaiu
Key Takeaways
- Calibrate the ocular micrometer to accurately measure microscopic objects.
- Use mechanical stages for systematic slide movement.
- Employ camera lucidas or microphotographic apparatus for detailed object reproduction.
Practical Tips
- Always ensure the high-power objective is correctly calibrated before making measurements.
- Use a mechanical stage to systematically cover the field of view during microscopic examination.
- For detailed reproductions, use a camera lucida or microphotography instead of freehand drawing.
Warnings & Risks
- Objects as small as a thousandth of a millimeter can be accurately measured by the ocular micrometer, but ensure precise calibration to avoid errors.
- Moving slides manually is tiresome and may lead to loss of focus; use mechanical stages for better control.
- Artificial lighting with an unvarying candle-power should be used when making microphotographs for more uniform results.
Modern Application
While the techniques described in this chapter are rooted in historical practices, they still hold relevance today. Accurate microscopic measurement and imaging remain crucial in various fields such as botany, medicine, and forensic science. The principles of calibration and systematic observation have been refined but not fundamentally changed. Understanding these methods can enhance modern survival preparedness by providing a foundation for advanced techniques and equipment.
Frequently Asked Questions
Q: How do you calibrate the ocular micrometer?
To calibrate the ocular micrometer, place one hundred lines of the ocular over seventy-five lines of the stage micrometer. This will allow you to calculate the value of each line of the ocular and ensure accurate measurements.
Q: What is the importance of using mechanical stages in microscopic examination?
Mechanical stages are important because they allow for systematic movement of slides, reducing the risk of losing sight of the object under observation and improving the coverage of the field of view during examination.
Q: Why should one use a camera lucida or microphotographic apparatus?
A camera lucida or microphotographic apparatus is necessary for making detailed reproductions of microscopic objects, which are particularly useful in research and documentation. These tools ensure that all details can be accurately captured and reproduced.