(granular leukocytes), white blood cells with specific granularity in their cytoplasm.

In invertebrate animals granulocytes are called granular amoebocytes. Granuloctyes are subdivided, according to the ability of their granules to be stained, into eosinophils (oxyphils), basophils, and neutrophils. Some vertebrate animals have functionally equivalent cells with oxyphilic granulation (pseudoeosinophils) instead of neutrophils. Granulocytes constitute the major portion of leukocytes in the blood of man. The percentage relationship between the various types of leukocytes changes with age, physiological condition, and the presence of illness. The nuclei of granulocytes are polymorphous; in neutrophils and eosinophils they are segmented. The granules of neutrophils and basophils are structureless; those of eosinophils contain unique “crystals.” It has been established that the neutrophilic granules are lysosomes, which contain hydrolytic enzymes. Granulocytes are capable of amoeboid movement and of phagocytosis. They are able to penetrate connective tissue (diapedesis) from the blood vessels and participate in inflammatory processes. Granulocytes are formed in special, hematopoietic organs.