Margination: At the site of infection, the velocity of blood flow decreases due to inflammatory exudates compressing the blood vessel. This leads to WBCs coming to the margin of the vessel wall from the central stream and this is termed as margination. Diapedesis: the cells put forth pseudopodia like processes and come out through the pores in the endothelial cell lining the capillaries to extra vascular compartment. +Ve chemotaxsis: the chemical substances (toxins) liberated by the bacteria acts as a chemo attractant and the leucocytes are attracted towards the bacteria. This is termed as positive chemotaxsis If the chemical substances liberated by bacteria are very strong (virulent), the leucocytes are repelled from the site of infection and is known as –ve chemotaxsis. Phagocytosis Proper: the pseudopodia put forth by the WBCs engulf the bacteria completely. Now the bacteria would be ready for the chemical degradation by the enzymes released by the leucocytes. Enzymatic Digestion: The various enzymes like lipolytic, proteolytic, lysozymes, hydrogen peroxide, superoxide, nitrous oxide etc act on the bacteria and bring about chemical degradation of the some. In the ensuing fight between the bacteria and neutrophils not only the bacteria get killed, even the leucocytes and some of the neighboring cells also get destroyed. This leads to the formation of the pus.