Introduction: Blood Cells
Blood contains several different types of cells. Some cells, such as red blood cells, carry oxygen to other cells. Other types of cells, such as white blood cells or leukocytes, provide protection from foreign cells and infectious agents. Cell fragments called platelets provide protection against bleeding. The red blood cells of different animals can have different structures.

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Still Image:
Human red blood cells
Individual disk-shaped red blood cells appear colorless when viewed under a microscope. The pink tint on the left of the image is due to the clotting of several layers of red blood cells. (Images of individual human, sheep, and zebrafish red blood cells were taken at the same magnification and appear to scale.)
A drop of blood was diluted in saline solution, then sandwiched between a slide and coverslip (using a thin strip of silicon rubber as a spacer). The image was taken on an inverted compound microscope using a 40x DIC objective and a digital camera.