Sentence:  In our work the best procedure for removing <WSD>substances</WSD> causing nonspecific staining in order to obtain specific conjugates was to pass the conjugates through a DEAE-cellulose column and in some cases to absorb the first and second milliliter fractions with sweet clover tissue powder . 
Meaning of the word marked with <WSD> tags:  the real physical matter of which a person or thing consists