Question

1. What is a differential stain?

2. Give three reasons for using heat as a fixative in Gram staining.

3. What is the use of the stage and ocular micrometer in micrometry.

Answer 1

Ans 1: Differential Staining is a staining process which uses more than one chemical stain. Using multiple stains can better differentiate between different microorganisms or structures/cellular components of a single organism. Differential staining is used to detect abnormalities in the proportion of different white blood cells in the blood. The process or results are called a WBC differential. This test is useful because many diseases alter the proportion of certain white blood cells.

2: Reasons for using heat as a fixative in Gram Staining are:

a) Heat fixing denatures bacterial enzymes, preventing them from digesting cell parts, which causes the cell to break, a process called autolysis.

b) Heat fixing kills the bacteria in the smear, firmly adheres the smear to the slide.  

c) Heat fixing allows the sample to more readily take up stains.

3: An ocular micrometer is a glass disk that fits in a microscope eyepiece that has a ruled scale, which is used to measure the size of magnified objects. The physical length of the marks on the scale depends on the degree of magnification.

A Stage micrometers are used on the stage of the microscope and provide a simple and reliable means of accurately calibrating eyepiece graticules.