X-ray of a human chest showing evidence of pulmonary tuberculosis in the patient's left lung. The disease is caused by the rod-shaped bacterium Mycobacterium tuberculosis. When inhaled into the lungs, the bacteria form a primary tubercle (nodular lesion). They then spread to the nearest lymph nodes. This form is called pulmonary tuberculosis or consumption & phthisis (wasting). Many people are infected without showing symptoms. Despite the immune system's ability to hold the disease in check, these people remain carriers, transmitting the bacilli by coughing or sneezing. Symptoms of the disease include fever, weight loss, night sweats & spitting of blood.