False-colour transmission electron micrograph (TEM) of a rod-like bacterium, Mycobacterium tuberculosis, the causative agent of tuberculosis in humans. This bacterium forms filamentous, branching structures, which are inhaled into the lungs to form a primary tubercle, an initial focus of infection; spread takes place via adjacent lymph nodes. This form is called pulmonary tuberculosis or consumption & phthisis (wasting). Many people are infected without showing symptoms, whilst the body's immune system holds the disease in check. They remain carriers, transmitting the bacilli by coughing or sneezing. Magnification: x18,000 at 35mm size, x36,000 at 6x7cm size.