Sentence:  In the present work whole sera have been fractionated by chromatography on DEAE-cellulose using single gradients similar to those described by Sober and Peterson , and certain chemical and serological <WSD>properties</WSD> of the fractions containing antibodies of the ABO and Rh systems have been described . 
Meaning of the word marked with <WSD> tags:  a basic or essential attribute shared by all members of a class