EXERCISE NO. 2 THE OCULAR MICROMETER

Question 1

The identification of parasites depends on several factors, one of which is size. The [?] are measured and are generally within a specific range.

Answer 1

length and width

Question 2

There are different ways by which size can be assessed. The size can be estimated in relation to the microscope field which can be determined for each set of (?) and (?). This is called the (?). However, this technique is limited to larger object images. It would be a little difficult to compare very small object image in relation to the view field.

Answer 2

eyepiece field number and objective magnification

actual field of view

Question 3

Jjk

Question 4

Another method of measuring is to compare the (?) with one of another object or parasite species common in the locality whose size under the microscope is known (e.g. red blood cells, or eggs of Ascaris)

Answer 4

parasite size

Question 5

Any laboratory doing diagnostic work in parasitology should have a (?) available for precise measurements.

Answer 5

calibrated microscope

Question 6

Measurements of objects microscopically are made with an (?) (also known as the reticule). The ocular micrometer is a disc made of glass that is inserted into the eyepiece of the microscope

Answer 6

ocular micrometer

Question 7

The (?) is etched with a measuring scale which is evenly divided into 50 or 100 units

Answer 7

micrometer disc

Question 8

the (?) on the ocular micrometer represents different measurements as it changes with total magnification, and thus has no absolute value.

Answer 8

scale

Question 9

does not have units and it needs to be calibrated prior to use

Answer 9

ocular micrometer

Question 10

looks like a glass slide but has a scale of known true length etched on the surface

Answer 10

stage micrometer

Question 11

typical stage micrometer scale is (?) long and etched with divisions of (?)

Answer 11

1. 0 mm

0. 01 mm

Question 12

It is just like a ruler and used to calibrate the ocular micrometer

Answer 12

stage micrometer scale

Question 13

With the ocular micrometer set correctly inside the eyepiece, the stage micrometer is focused with an (?) (usually starting with the lowest power) of the microscope, making sure to make the scale as sharp as possible.

Answer 13

objective

Question 14

can be rotated and the stage micrometer is moved on the microscope stage so that the two scales are parallel to each other

Answer 14

eyepiece

Question 15

identified by the numbered divisions

Answer 15

ocular micrometer scale

Question 16

does not show numbers but true lenght of each division is known (0.01 mm)

Answer 16

stage micrometer scale

Question 17

simply superimpose the (?) onto the stage micrometer and note the relationship of the length of the ocular to the stage micrometer

Answer 17

ocular micrometer

Question 18

When making measurements, it’s particularly important that the right (?) of measurements are used.

Answer 18

units

Question 19

Measurements of parasites observed under the microscope are usually reported in

Answer 19

microns, µ

or micrometers, µm

Question 20

One mm is equal to

Answer 20

1000 (µm)

Question 21

The figures obtained from the calculations should be converted to (?) during measurements

Answer 21

micrometers

Question 22

Each (?) of the microscope must be calibrated separately.

Answer 22

objective

Question 23

is different at each magnification

Answer 23

calibration factor

Question 24

The calibrated ocular micrometer can be used to measure any (?) in a microscope field since the ocular can be turned in any direction to align with the length or width of the object.

Answer 24

planar dimension

Question 25

To measure the length or width of an object note the number of (?) spanned by the object. Then multiply by the calibration factor for the magnification used

Answer 25

ocular divisions

Question 26

•After each (?) has been calibrated, the oculars containing the disc and/or these objectives cannot be interchanged with corresponding objectives or oculars on another microscope.

Answer 26

objective

Question 27

•Each microscope used to measure organisms must be calibrated as a (?). The original oculars and objectives that were used to calibrate the microscope must also be used when an organism is measured.

Answer 27

unit

Question 28

•The (?) containing the ocular micrometer can be stored until needed. This single ocular can be inserted when measurements are taken. However, this particular ocular containing the ocular micrometer disc must also have been used as the ocular during microscope calibration.

Answer 28

eyepiece

Question 29

•Post the (?) for each objective either on the base of the microscope or on a nearby wall or bulletin board for easy reference.

Answer 29

calibration factor

Question 30

•(?) is usually repeated annually.

Answer 30

Calibration

Question 31

``` •When the high dry and oil immersion objectives are used, the 0 line of the stage micrometer will (?), whereas the ocular 0 line will (?). The thin ocular 0 line should be lined up in the center or at one edge of the broad stage micrometer 0 line. Thus, when the second set of superimposed lines is found, the thin ocular line should be lined up in the center or at the corresponding edge of the broad stage micrometer line ```

Answer 31

increase in size | remain the same size

Question 32

Ability to measure accurately the size of parasitic forms is often necessary in making species identification. This measurement can be made with a calibrated scale called

Answer 32

micrometer

Question 33

are flat glass discs etched with a fixed scale, usually consisting of 50 or 100 small divisions. These divisions will have different measurement values depending on the power of the microscope objective used

Answer 33

Ocular micrometers

Question 34

The measurement values are calculated using a (?) etched with a known calibrated scale of 0.1 mm divisions subdivided into 0.01 mm divisions

Answer 34

stage micrometer

Question 35

1. Remove the (?) (lOx or other) from the microscope and unscrew the top or bottom lens, depending on its construction. Place the (?) on the diaphragm within the eyepiece with the etched surface on the undersurface of the reticule. Screw back the (?) and re-insert the eyepiece into the microscope

Answer 35

eyepiece ocular scale lens

Question 36

2. Place the (?) on the microscope stage and focus the low-power objective on some portion of the scale with the lOx eyepiece.

Answer 36

stage micrometer

Question 37

3. Adjust the stage micrometer by moving the stage so that the 0 line of the (?) is exactly superimposed on the 0 line of the stage micrometer

Answer 37

ocular micrometer

Question 38

4. Without moving the stage micrometer, find another point at the (?) where two other lines are exactly superimposed. This second set of superimposed lines should as far to the right as possible from the 0 lines. This distance will vary with the (?) used. At higher magnifications, the thickness of the (?) may be great that you need to look for superimposition of either the left or right edge of the individual lines

Answer 38

extreme right objective etched lines

Question 39

5. Count the number of (?) on the ocular micrometer between the 0 line and the point where the second set of lines is superimposed. In the example provided in the figure, this number, indicated by the dotted line, equals 33 ocular units

Answer 39

division lines

Question 40

6. Then count the number of (?) division lines between the 0 line and the second superimposed line on the stage micrometer; in the figure, this number, indicated by the arrowhead, equals 0.22 mm

Answer 40

0.1 mm

Question 41

7. Calculate the length represented by

Answer 41

one ocular unit

Question 42

8. When all the objective have been calibrated, prepare a simple chart that displays the (?) for each one

Answer 42

calibration factor

Question 43

1. With the ocular micrometer in place after calibration, focus on the object to be measured and determine the size in

Answer 43

ocular units

Question 44

2. Calculate the size of the object by multiplying the (?) by the (?) for that specific microscope, objective and ocular micrometer

Answer 44

ocular units by the calibration factor

Question 45

The (?) are arbitrary and a calibration procedure must be done to determine the calibration factor for each different objective and each different microscope

Answer 45

units of the micrometer disc