They are found less in number in the blood as compared to the red blood corpuscles, the ratio being about one white blood corpuscle to every 6 hundred red blood corpuscles.
These are formed in the red bone marrow and in the lymph glands. Normally there are between 600 to 800 white blood corpuscles in one cubic millimeter of blood as against four and a half to five million red blood corpuscles.
These corpuscles contain nuclei and somewhat larger in size in comparison to the erythrocytes. These vary in size.
They are actively motile and capable of amoeboid movement. Their chief function is to check the invasion of the small organisms like bacteria and other foreign substances into the body.
This they do in two ways:
1. Some white blood corpuscles engulf the invading organisms in the manner of Amoeba ingesting a particle of food, the manner is commonly known as phagocytosis.
This phenomenon was first discovered by Metschnik off and named phagocytosis (Gr. phagein-to eat).
The white blood corpuscles as they take part in phagocytosis, are referred to as phagocytes.
2. Other white blood corpuscles secrete into the plasma antibodies which are chemical substances capable of neutralizing poisonous (toxic) chemicals in the blood such as the poisonous waste materials passed out by bacteria.
The mature white blood corpuscles can be grouped into two main categories: granular leucocytes or granulocytes and agranular leucocytes or agmnulocytes depending upon whether their cytoplasm contains visible granules or not.