Final answer:
A researcher might use a microscope slide to count bacteria using a Petroff-Hausser counting chamber, or to count different types of white blood cells in a blood sample for clinical diagnostic purposes.
Step-by-step explanation:
A researcher might make a microscope slide for counting cells such as bacteria, which can be done using a Petroff-Hausser counting chamber or a hemocytometer. This method is known as a direct microscopic cell count. The researcher uses these calibrated slides to accurately count the number of cells in a given volume, typically for the purpose of estimating the concentration of cells in the original sample. The samples can be stained or unstained, depending on the requirements of the experiment. For instance, if a researcher wants to measure the concentration of bacteria in a given culture, they will transfer a known volume of the culture to the counting chamber, and count the individual cells under a light microscope.
Another common example is counting white blood cells in a blood sample. In this instance, a prepared slide of Wright stained blood smear is used to identify and count different types of white blood cells. This is crucial for clinical diagnostics as variations in white blood cell counts can indicate various health conditions.