Sentence:  Treatment of the conjugates with ethyl acetate , and the conjugates ( which had been passed through Dowex-2-chloride ) with mouse liver powder , sweet clover crown gall tissue powder , or healthy sweet clover proteins did not satisfactorily remove nonspecifically <WSD>staining</WSD> substances in the conjugates . 
Meaning of the word marked with <WSD> tags:  the act of spotting or staining something