Blood Cell.

http://en.wikipedia.org/wiki/Blood_cell

A blood cell, also called a hematocyte, is a cell produced by hematopoiesis and normally found in blood. In mammals, these fall into three general categories:

• Red blood cells – Erythrocytes
• White blood cells – Leukocytes
• Platelets – Thrombocytes.

Together, these three kinds of blood cells add up to a total 45% of the blood tissue by volume, with the remaining 55% of the volume composed of plasma, the liquid component of blood.This volume percentage (e.g., 45%) of cells to total volume is called hematocrit, determined by centrifuge or flow cytometry. Hemoglobin (the main component of red blood cells) is an iron-containing protein that facilitates transportation of oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs.

Red and white human blood cells as seen under a microscope using a blue slide stain.