The leucocytes are commonly known as white blood corpuscles (cells). The leucocytes are colourless and do not contain haemoglobin. They are larger than red corpuscles and much less in number. For every leucocyte present in the blood there are about 700 erythrocytes, i.e. The ratio of red blood cells to leucocytes is 700:1. Each leucocyte is irregular in shape and contains a nucleus. It can move. It can change its shape and squeeze through the walls of the fine blood vessels into the spaces among the tissue cells. There are two main kinds of leucocytes: Lymphocytes and phagocytes. Lymphocytes are produced by the lymph glands or lymph nodes. Each lymphocyte has a large, rounded nucleus and a relatively small amount of non-granular cytoplasm. Lymphocytes tend to be nearly round in shape and only show limited movements. Phagocytes are produced by the bone marrow. They are so called because they can ingest foreign particles like bacteria. There are two kinds of phagocytes namely monocytes and polymorphs. A monocyte has a beam-shaped nucleus. A polymorph has a nucleus with many lobes and granular cytoplasm. The white blood cells play a pivotal role in keeping the body healthy. Though they contain a nucleus, their normal life span, at least in the blood stream, is only a few days.
