What is cell fixation?

In order to study tissues in detail under a microscope, it’s important that they are properly preserved (fixed) and cut into thin, translucent sections. This is what cell fixation does. It preserves biological tissues by terminating ongoing biochemical reactions which would otherwise cause decay due to putrefaction or autolysis. This is a crucial first step in the preparation of histological sections. If cell fixation is not carried out or even if it is delayed, the tissue specimen could get permanently damaged and compromise the morphological and histochemical information that is obtained from the sample tissue. 

Cell fixation serves three main purposes: 

1. It protects the specimen from intrinsic damage by deactivating proteolytic enzymes and other biomolecules which would digest or damage the sample. 
2. It protects the specimen from extrinsic damage by nature of being toxic to most common microorganisms such as bacteria that may otherwise colonize the sample and damage it.  
3. It increases the mechanical strength and stability of cells and tissues, which helps preserve the shape and structure of the sample, making it easier to cut into thin sections for further analysis.