What is the first step in the process of heat-fixing a slide?

The first step in the process of heat-fixing a slide is passing it through a flame. This is a crucial initial step as it serves to adhere the microbial specimens to the glass slide, preventing the cells from being washed away during subsequent staining procedures. The heat kills the bacteria, ensuring they are fixed in place and maintains the integrity of their structures for microscopic examination.

This process also serves to reduce the possibility of contamination and allows the coloring from stains to penetrate the cells more effectively, which is essential for enhancing the visibility of the specimen under a microscope. Other options, although they are part of the preparation or staining processes, do not align with the fundamental first step that ensures proper adherence and fixation of the samples on the slide.