Final answer:
To count white blood cells, a light microscope and a stained blood smear are required. Scanning patterns and visual aids help in identifying and counting the various types of leukocytes, which play a crucial role in the immune system.
Step-by-step explanation:
To count white blood cells (WBCs) in a blood sample, a light microscope is typically used due to the small size of these cells, which range from 12-15 micrometers (µm) in diameter. A prepared blood smear stained with a dye such as Wright's stain allows for the differentiation and counting of WBCs. As a point of reference, a red blood cell is about 8 µm in diameter.
Scanning a prepared slide under a microscope and manually counting the white blood cells until you reach a certain number (often 100 cells) is a method to get an estimate of the WBC count in the sample. The number of leukocytes, a type of WBC, varies among different species and typically is measured in thousands per microliter of blood (µl). For humans, a healthy leukocyte count ranges from about 1,000 to 11,000 cells per µl.