Serum

Serum, clear yellowish fluid that separates from blood, lymph, and other body fluids when they clot. It contains water, proteins, fat, minerals, hormones, and urea. Serum therapy involves injecting serum (obtained from humans or horses) containing antibodies (globulins) that can destroy particular pathogens. Occasionally injected serum gives rise to an allergic reaction known as serum sickness; a second injection of the same serum may induce anaphylaxis (hypersensitivity).

See also: Gamma globulin; Plasma.