Plural of serum; the clear liquid components of blood that remain after clotting, used in medical treatments and research.
Latin plural of 'serum' meaning 'whey, watery fluid'. From the same root as 'serous', originally referring to the watery part of milk (whey). Medical usage began in the 17th century when scientists noticed blood's liquid component after coagulation.
Sera were humanity's first targeted medicines—using antibodies from recovered patients to treat diseases before we understood how immunity worked. From snake bite treatments to early vaccines, sera represented our first successful attempt to transfer biological protection between individuals.
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