Se"rum (sē"rŭm), n. [L., akin to Gr. ???, Skr. sāra curd.] (Physiol.) (a) The watery portion of certain animal fluids, as blood, milk, etc. (b) A thin watery fluid, containing more or less albumin, secreted by the serous membranes of the body, such as the pericardium and peritoneum.

Blood serum, the pale yellowish fluid which exudes from the clot formed in the coagulation of the blood; the liquid portion of the blood, after removal of the blood corpuscles and the fibrin. -- Muscle serum, the thin watery fluid which separates from the muscles after coagulation of the muscle plasma; the watery portion of the plasma. See Muscle plasma, under Plasma. -- Serum albumin (Physiol. Chem.), an albuminous body, closely related to egg albumin, present in nearly all serous fluids; esp., the albumin of blood serum. -- Serum globulin (Physiol. Chem.), paraglobulin. -- Serum of milk (Physiol. Chem.), the whey, or fluid portion of milk, remaining after removal of the casein and fat.