Illustration of a section through the spleen showing Malpighian corpuscles (darker). Situated on the left side of the upper abdomen, behind the stomach, the spleen is a large lymphoid organ. The interior consists of nodules of white pulp, known as Malpighian corpuscles, within a matrix of red pulp. The red pulp is responsible for filtering blood by removing any foreign objects or worn out red blood cells. The white pulp contains immune system cells that respond to any pathogens in the blood.From 'Traite d'Anatomie Humaine' (1905) by French anatomist Leo Testut (1849-1925).