This document discusses different methods of micrometry, which is the measurement of microscopic objects under a microscope. There are two main types of micrometers used: stage micrometers and ocular micrometers. Stage micrometers have finely graduated scales etched onto a slide and are used to calibrate the microscope by observing how many divisions on the ocular micrometer correspond to a known distance on the stage micrometer. Ocular micrometers are discs that are inserted into eyepieces and have their own graduated scales. To measure a microbe, its size is calculated by counting how many divisions it spans on the calibrated ocular micrometer. Micrometry is important in microbiology labs to identify microscopic organisms by measuring their length.

1. MICROMETRY
U.DEEPALAKSHMI
I M.Sc MICROBIOLOGY

2. Introduction:
Microorganisms are microscopic
objects that are visible only with the help of
a microscope. Sometimes it is necessary to
measure its dimensions for its identification
process. But determination of the size of a
microorganism is not an easy process.

3. Micrometry:
Micrometry refers to the measurement of
dimensions of the desired microorganisms
under a microscope which uses two micro-
scale known as micrometers. These are two
types

4. Types of Micrometry:
There are usually two types of
micrometers
Stage micrometer.
Ocular meter or ocular micrometer.

5. Stage micrometer:
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. In the centre of
the stage micrometer a known 1mm distance is
etched into 100 equally spaced divisions making
each divisions equals 0.01mm or 10micrometer.
1mm=100 division
1mm=1000mu

6. Ocular micrometer:
ocular micrometer with microscopic
graduations etched on their surface is a circular
glass disc that fits into the circular shelf inside
the eyepiece of the microscope.
It has 100 equally spaced divisions marked 0-
10. depending on the objective being used the
distance between these graduations will very
that determines the size of the field.

7. STAGE MICROMETER WORK FLOW:
The stage micrometer kept under the low
power microscope and is observed through the eye
piece having eyepiece reticle.
at this magnification the number of eyepiece
reticule coinciding the stage micrometer are
observed and thence calculated for microns per
ocular divisions.

8. The correct way to calibrate a
reticle with a stage micrometer is to
line up the left edges of each.
For ex;6 ocular division is
coincide with 8 division of stage
micrometer.

9. One ocular division = number of stage meter division
number of ocular meter division
=0.08/6
=0.08*1000/6
=13.3mu

11. Ocular micrometer works flow:
Insert the ocular meter in the eye piece of
your calibrated microscope by unscrewing its
upper eye lens.
Keep the spore or bacterial slide to be
measured on the stage of the microscope and
observe through the eyepiece containing ocular
meter.
The number of ocular divisions covered by
the microbe is counted by viewing through he
eye piece.

12. The size of the microorganism is
determined by multiplying the
number of ocular divisions covered
by the microbe with the calibration
factor.

13. Each cell occupy the 5
division so the answer
is 5*13.3=66.5u

14. Fig: ocular
micrometer

15. Application:
This method is more important in
microbiological laboratory.
The main purpose of this method to
identified the length if the organism
such as bacteria, virus, human RBC
cells, yeast cell etc..

16. Thank you