Sentence:  In our work the best procedure for removing substances 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 <WSD>second</WSD> milliliter fractions with sweet clover tissue powder . 
Meaning of the word marked with <WSD> tags:  coming next after the first in position in space or time or degree or magnitude