alexinyoudaoicibaDictYouDict[alexin 词源字典]
"A serum protein with bactericidal properties; specifically = complement", Late 19th cent.; earliest use found in The British Medical Journal. From German Alexin from ancient Greek ἀλέξειν to ward off (from the same Indo-European base as Sanskrit rakṣ- to protect) + German -in.[alexin etymology, alexin origin, 英语词源]