Final answer:
Heat fixation adheres a specimen to a slide by killing it, stopping its movement and metabolism, and securing it to the glass. Excessive heat from fixation can distort cells or cause a slide to crack. Chemical fixatives are preferred for delicate tissue specimens to avoid heat damage.
Step-by-step explanation:
Heat Fixation in Smear Preparation
The purpose of heat fixation when preparing a smear on a slide is to adhere the specimen to the slide surface securely. This method involves rapidly heating the slide with the specimen smear over a flame, often using a Bunsen burner. Heat fixation serves several functions: It kills the specimen, preventing degradation and preserving cellular components; it stops the specimen's metabolic processes and movement, which is crucial for examining cellular structures under a microscope; and it enhances the specimen's adherence to the glass slide, preventing it from washing away during subsequent staining steps.
However, improper heat fixation can lead to several problems. Excessive heat can cause the cells to rupture or become distorted, which would hinder accurate microscopic examination. Moreover, it can result in the slide cracking or the specimen being destroyed due to the high temperatures.
Chemical fixatives, including agents like acetic acid, ethanol, methanol, formaldehyde (formalin), and glutaraldehyde, are preferable to heat for delicate tissue specimens as they denature proteins, halt biochemical reactions, and stabilize cell structures without the extreme heat that can damage the tissue's morphology.