Final answer:
Heat-fixing is prohibited in preparing live cell or tissue slides, working with heat-labile substances, and on slides coated with heat-sensitive materials. Instead, chemical fixation using agents such as formalin, ethanol, or glutaraldehyde is often used.
Step-by-step explanation:
Heat-fixing is a method often used in microbiology to prepare microscope slides for viewing. However, there are certain procedures for which heat-fixing is prohibited due to the potential damage to the specimen or the slide. The procedures where heat-fixing is not recommended include:
- Preparing slides for observing live cells or tissues, as the heat would kill these specimens.
- When dealing with heat-labile substances, that is, materials that can be degraded or denatured at high temperatures.
- Handling slides that have been coated with substances that might melt or be altered under high heat, such as certain plastics or chemicals.
Instead of heat-fixing, chemical fixation is often the preferred method for these types of specimens. Chemicals like formalin, ethanol, and glutaraldehyde can effectively preserve cell and tissue structure for microscopic examination without the damage that heat may cause.