White Blood Corpuscles (WBCs) or Leucocytes: These are circular, amoeboid or irregular shaped, colourless, nucleated wondering cells. These have the capacity to squeez out from blood capillaries into tissue fluid where these destroy pathogens and foreign antigens to protect the body. There are about 6000 - 8000 WBCs/mm3 blood in a healthy adult man. They are produced in bone marrow, Peyer�s patches of intestinal mucosa, lymph nodes, thymus and spleen. The production of WBCs is called leucopoiesis. The average life span of WBCs is 4 - 7 days. There are the following two groups of white blood corpuscles: (A) Granulocytes (B) Agranulocytes (A) Granulocytes: There are many granules present in the cytoplasm of such types of WBCs and their asymmetrical nucleus is divided into two or more lobes. On the basis of shape of nuclei and staining reactions of the cells, the granulocytes are divided into following three types: (i) Neutrophils: Their nucleus is made of 2 - 5 lobes which are connected by thin threads. These are most active WBCs and measure 10 - 12 ? in diameter. These are also known as heterophils. These are about 60 - 65% of total leucocyte count. Their granules are smaller but more numerous and can be stained by acidic or alkaline, both types of stains. Their granules are actually lysosomes and Golgy bodies. Their main function is to destroy pathogens therefore these acts as phagocytes. (ii) Eosinophils: Their nucleus is divided into two clear lobes. Both the lobes are connected with filament. Eosinophils measure 10 - 15 ? in diameter and form 2 - 4% of total leucocyte count. These have larger granules and are stained by acidic stains like eosin. Their exact functions is not known but their number is increased many folds during allergy and infection. (iii) Basophils: Their nucleus is made of 2 to 3 lobes or �S� shaped. These are granulocytes measuring 8 - 10 ? in diameter and form 0.5 - 2% of total leucocyte count. Their granules are less numerous but relatively larger in size and can be stained with basic dyes like methylene blue. Bosophils secrete heparin and histamine. Hiparin is an anticoagulant and histamine promotes inflammatory reaction. B. Agranulocyles: Cytoplasm of such type of WBCs is agranular and their nucleus is spherical, without lobed. These are of two types: (i) Lymphocytes: These are smallest WBCs and measure 8 - 12 ? in diameter. These form 30% of total WBCs. Their nucleus is spherical and large in size, therefore, the cytoplasm is restricted to peripheral rim only. On the basis of their size these are grouped as small and large lymphocytes. Lymphocytes are produced in lymph glands. Their main function is to produce antibodies. (ii) Monocytes: These are comparatively large sized and measure 12 - 15 ? in diameter. These form about 6% of total leucocyte count. These have large, horse - shoe - shaped nucleus. These are produced in lymph nodes and spleen. These are actively wondering cells engaged in phagocytosis, and are converted into macrophages after reaching tissue fluid. In tissue fluid, these dispose off as dead or worn out cells.