Blood smear. Sample of blood being prepared for analysis under a microscope. A drop of blood has been placed on one end of a microscope slide and a spreader slide is about to be used to smear the blood across the slide. Smears are prepared to aid in diagnosing illness. Technicians examining the slide under a microscope may count blood cells or identify pathogens, such as blood parasites. Gloves are worn when preparing such slides to avoid contamination. These are nitrile gloves, which are latex-free.