Lymph node. Light micrograph of a section through a healthy human lymph node. The follicles (oval, purple) are the regions in which B-lymphocyte white blood cells proliferate. Surrounding the lymph node is a collagenous capsule (pink, at left). This supportive tissue extends into the node as a trabecula (pink). Lymph nodes are kidney-shaped organs into which the fluid from body tissues drains and is filtered. The nodes are packed with white blood cells that destroy disease-causing microorganisms within the fluid. The granular appearance of the tissue is caused by the presence of thousands of lymphocyte white blood cells. Magnification: x400 at 35mm size.