What is a complex nitrogenous radical, C8H4NO2, regarded as the essential residue of a series of compounds, related to isatin, which easily pass by reduction to indigo blue. -- I*sat`o*gen"ic, a called?

isatogen — A complex nitrogenous radical, C8H4NO2, regarded as the essential residue of a series of compounds, related to isatin, which easily pass by reduction to indigo blue. -- I*sat`o*gen"ic, a. (Webster's 1913.)

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