CBSE Class 9 Answered

Pus is the thick white or yellowish fluid that forms in areas of infection such as wounds. It is constituted of decomposed body tissue, bacteria or other micro-organisms that cause the infection and certain white blood cells. When the need to fight infection arises, the neutrophils move to the site of infection by a process known as chemotaxis. At the site of infection they engulf and kill bacteria. Eventually, the neutrophils die, and these dead cells are then phagocytosed by macrophages, which break them down further. Pus, therefore, is the viscous material composed of these dead neutrophils and the dead cells of the body, along with the pathogens.