Sentence:  Abelson and Rawson , using a stepwise elution scheme , fractionated whole <WSD>sera</WSD> containing ABO and Rh antibodies on diethylaminoethyl DEAE cellulose and carboxymethyl cellulose . 
Meaning of the word marked with <WSD> tags:  an amber, watery fluid, rich in proteins, that separates out when blood coagulates