MEASUREMENT OF HUMAN HAIR THICKNESS BY MICROSCOPE

The microscope is the optical device that enlarges the resolving power of the eye. It consists of four basic parts. Two optical parts are called the objective and the eyepiece. The objective is a lens close to the object being viewed to collect light which focuses a real image of the object. The image is then magnified by a second lens (eyepiece) that gives an enlarged inverted virtual image of the object. The use of compound objective/eyepiece combination allows for much higher magnification (Figure 1). The third part is the illuminating part that ensures sufficient illumination of the object observed. The fourth one is the mechanical part with revolving holder of objectives and with micro- and macro screw for focusing (Figure 2).

Figure 1: Magnification of object with objective lens and eyepiece.

Figure 2: Basic parts of light microscope.

Parameters of the objective are its focal length (fo) and the optical tube length (Δ). The transverse magnification (Mo) of the objective is given by the equation: Mo =

∆ fo

where Δ corresponds to the smallest distance between focal points of the objective and the eyepiece. The transverse magnification of the eyepiece (Me) is given by: Me =

0.25 fe

where fe is the focal length of the eyepiece. The total transverse magnification of the microscope (M) is given by: M = Mo ∙ Me =

0.25 ∙ ∆ fo ∙ fe

and it can be of about 2000 or 3000 at maximum for optical microscope.

Devices and aids: 1. Microscope 2. Objective micrometer for calibration of the eyepiece division scale 3. Set of supporting and covering glasses 4. Dropping device Task: Measure the thickness of human hair Implementation: 1. Prepare of about 5 preparations of the human hair of various persons. Cut about 5 mm of the hair, put it on the supporting glass, drop on it several drops of water and cover with the cover glass. 2. Switch on the light source of the microscope. 3. Calibrate the eyepiece scale with the help of objective micrometer for the objective with magnification of 40x. The objective micrometer represents the scale placed inside the small ring of the glass plate. The scale is 1 mm long and is divided into 100 parts (Figure 3). Thus, one part of the scale corresponds to 10 µm. Put the objective micrometer on the microscope, fix it and focus its scale. By comparison of the scale parts with those of the eyepiece, determine the value of one small part of the eyepiece scale. Notice, that the eyepiece scale within the range of 0 – 10 big sections really represents 100 parts. Put the objective micrometer into the scale.

Figure 3: Objective micrometer.

Important caution: 1. To prevent the damage of the objective or of the preparation, use simultaneous control by eye when focusing. After the preparation is approached by the objective, increase the objective distance from the preparation by using the micro screw. 2. Put one sample of the human hair on the microscope table, fix it and focus its image and arrange it into the centre of the field of vision by using the table shift. 3. Measure the hair thickness of the first preparation at five points and note the results. 4. In the same way measure the hair thickness in remaining four preparations. 5. Switch off the light source. Evaluation: 1. Write all measured values in the table of your report. Calculate the average values and probable error of the result from five measurements on the hair thickness carried out on one preparation. 2. Summarize these results for individual preparations in a table of your report.

MEASUREMENT OF THE SIZE OF ERYTHROCYTES

Under normal conditions, the size of the human erythrocytes corresponds to 7.2 ± 0.2 µm. Enlarged or reduced size of erythrocyte can indicate a serious failure in the health condition of a patient. Red blood cells smaller than normal are seen in iron or pyridoxine deficiency, anemia and in hyperosmolar environment. Red blood cells larger than normal we can find in vitamin B12 or folate deficiency, liver diseases, hypoosmolar environment or after chemotherapy. In addition to size, variation in shape and color is also important.

Devices and aids: 1. Microscope 2. Objective micrometer for calibration of the eyepiece division scale 3. Set of supporting and covering glasses 4. Fixed stained smears of periphery human blood. Task: Measure the size of 10 erythrocytes in the blood smear Implementation: 1. Switch on the light source of the microscope. 2. By turning the revolver holder of objectives place the objective magnifying 40x. 3. Calibrate the eyepiece scale by the objective micrometer for the objective as described in the previous instruction. 4. Put aside the objective micrometer into the case. 5. Put the preparation with smear on the microscope table. 6. Measure the erythrocytes size but not from the dense part of the smear (Figure 4).

Figure 4: Find a part of the smear with a fewer cells. Then you can measure the size with greater accuracy.

7. Repeat these measurements for subsequent 9 erythrocytes. 8. Switch off the light source. 9. Put the preparation into the case. Evaluation: Calculate the average value and probable error of result from 10 measurements of the erythrocyte size and write the result in your report.