MEASUREMENT OF CELL
SIZE:
Meaning of Micrometry:
• Micrometry is the science in which we have
some measurement of the dimensions of an
object being observed under the microscope.
The method employs some special types of
measuring devices which are so oriented that
these can well be attached to or put into the
microscope and observed. The object, to be
measured, is calibrated against these scales.
MICROMETER
• Once we are observing an object under a
microscope by the 5X objective and the 10X
eyepiece we say that the image that we are able
to perceive is 5 × 10 = 50 times of the object.
• We get the magnified view no doubt and also that it is the
perfect coordination of the dimensions, but to find out the
exact size of the object will need precision and that is
achieved through the application of some small scales
called micrometers.
Types of Micrometry
TWO TYPES OF MICROMETERS:
1. stage micrometer
2. ocular meter or ocular micrometer
Stage Micrometer
• As is clear from its name it is for the measurement
on the stage of the microscope where an object is to
be kept. This micrometer is of a slide’s shape and
size and has a mount of very finely graduated scale.
The scale measures only 1 mm and has a least count
of 0.01 mm, i.e. 1 mm region is divided into 100
divisions. As 1 mm has 1000µ, one division of stage
micrometer is equivalent to 10µ.
Ocular Meter
• This micrometer is used inside the eyepiece.
The upper eye lens is unscrewed and the ocular
meter is put into the tube of eyepiece, and the
eye lens is again replaced in its original
position. There are usually 50 or 100 divisions
in the ocular meter which are engraved on the
glass.
Objective
•To measure the dimensions of
common microorganisms by
calibration and standardization of
microscope using stage micrometer
and ocular micrometer.
Requirements:
1. Microscope
2. stage micrometer
3. ocular meter
4. slide of the microorganism to measured.
Procedure
• To work out the measurements per ocular
divisions the stage micrometer is kept under low
power of microscope and is observed through
the eyepiece having ocular meter.
• Suppose we have 10 X objective and 5 X
eyepiece fitted in the microscope with a tube of
170 mm length.
Procedure
• At this magnification the number of ocular divisions coinciding the stage micrometer are
observed and then calculated for microns per ocular divisions
• Example: Let us take that 5 ocular divisions coincide with 7 divisions of stage micrometer.
• We know 1stage div. =0.01mm or 10μm
• So when 5 ocular divisions coincide with
7 divisions of stage micrometer that means
5 ocular div= 7 stage div. or 70 μm
Now we have to calibrate 1 ocular div=? μm
Procedure
• 5 ocular division = 70 μm stage div.
(cross multiply)
• 1 ocular division= 70/5 ×1= 14 μm
• So, 1 ocular div. is equal to14µ where 1stage div.=10 μm
Or, it can also be calculated by following formula:
• One division of ocular = Number of stage micrometer
divisions/Number of ocular meter divisions × 10
• In the case mentioned above it will be
= 7 × 10/5µ = 14µ.
Procedure
In this way the microscope is calibrated for different
combinations of eyepieces and objective lenses and is kept
for record. It is to note that this calibration will be just only
of the tried lenses on this particular microscope.
Measurement of the Microorganisms
• When the microscope is calibrated, then the object or
organism to be measured is kept on the sage of the
microscope and is observed through the eyepiece with
ocular. The object is measured in the particular
magnification by ocular divisions and then is changed into
microns by multiplying ocular divisions with calibrated
value of one ocular division in that particular
magnification.
Procedure
• Suppose the diameter of an object (Fig. 107) is observed to be equal to 6 divisions of
ocular, so the diameter of this object in microns will be:
6 × 14µ = 84µ
(where 14µ is the value calculated as 1 ocular division)
• In this way the object is measured in different
magnifications.