Spleen, light micrograph. The spleen shows many lymphoid follicles stained blue and termed the white pulp. Between the follicles is the red pulp comprising blood, blood vessels and a supporting connective tissue. Acting as a filter for blood the spleen functions as an immune surveillance organ capable of initiating an immune response from the lymphocytes concentrated in the lymphoid follicles. The indentation in the spleen is the conduit for splenic vessels. Paraffin section, haematoxylin and eosin stain. Magnification: x4 when width printed at 10cm.