Light micrograph of a section through a lingual tonsil (bottom), which is located at the base of the tongue (top) at the back of the mouth. The tonsils, part of the immune system, are large lymphatic nodules in a mucous membrane. Each tonsil consists of lymphoid follicles (purple) that contain lymphocyte white blood cells. Mucous glands (pale blue. Magnification: x40 when printed at 15cm tall.