Light micrograph of tissue infected with Madurella mycetomatis fungus (pink) from a patient with black grain mycetoma. M. mycetomatis can cause black grain mycetoma in humans, an infection of the subcutaneous tissue (deepest layer of skin), where black grains are present in discharge from the infection site. The proliferating fungus causes purulent swellings and boils. In later stages destruction of deeper tissues may occur, causing deformity and loss of function. Treatments include long-term antifungal medication. Sample stained by Gridley's method.