Sentence:  Two absorptions of * * f with ethyl acetate or two absorptions of * * f ( which had been passed through Dowex-2-chloride ) , NS and * * f with crown gall tissue powder , or mouse liver powder did <WSD>not</WSD> further improve the specificity of staining . 
Meaning of the word marked with <WSD> tags:  negation of a word or group of words