Fixation

Fixation is defined as the process of preserving and fixing the internal and external stucture of the cells into position. As a rule of fixation, a microorganism is killed & firmly attached to microscopic slide. The process of fixation basically inactivates the enzymes that might disrupt the cell morpholgy and thereby toughens the cell structures so that they do not change during staining & observation procedures. This process helps stained cells to resemble living cells as closely as possible.

There are basically two types of fixation – Heat fixation and Chemical fixation.

Heat fixation helps in preserving the overall morphology of the cell but not the internal structures. It is done by passing the slide, containing bacterial smear, 3 to 4 times quickly through upper portion of the flame.

Chemical fixative generally penetrates the cell and reacts with the cellular components like lipids and proteins thereby making them inoluble, inactive and immobile. Chemical fixation is generally used to protect fine cellular structures & the morphology of larger and more delicate microbes. Some common examples of chemical fixatives are the mixture of acetic acid, formaldehyde, ethanol, mercuric chloride and glutaraldehyde.