Sentence:  In the present work whole sera have been fractionated by <WSD>chromatography</WSD> on DEAE-cellulose using single gradients similar to those described by Sober and Peterson , and certain chemical and serological properties of the fractions containing antibodies of the ABO and Rh systems have been described . 
Meaning of the word marked with <WSD> tags:  a process used for separating mixtures by virtue of differences in absorbency