During the course of tuberculosis- infection bacteria, the inhaled bacteria enter the lungs, where they multiply and cause a local lung infection. The surrounding lymph nodes may also become involved and usually increase in size. The body's immune system tries to fight off the infection, and stop the bacteria from spreading to other parts of the body, by forming scar tissue around the TB bacteria and isolating it from the rest of the body. If the body is able to form scar tissue (also known as fibrosis) around the TB bacteria, then the infection is contained in an inactive state. Such an individual typically has no symptoms and cannot spread TB to other people. The scar tissue and lymph nodes may eventually harden, like stone, due to calcium deposition in the scar. These scars due to old healed tuberculosis lesions can be seen on x-rays. However, all cases of old treated TB may not lead to scar formation.