Specific Staining of Nucleolar Substance with Aceto-Carmine

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Abstract
A method is described for staining nucleoli intensely by treating tissues with formaldehyde, hydrolysing in normal HC1 at 60°C. and staining with aceto-carmine. With correct hydrolysis time, chromosomes and cytoplasm are almost colorless. Formaldehyde increases the acidity of cell parts, especially the nucleolus, presumably by neutralizing the basic protein groups, and increases the resistance to hydrolysis, perhaps by protecting the phospholipoprotein complexes which are most abundant in the nucleolus. Hydrolysis reduces the acidity of cell parts, chiefly by removal of nucleic acids. Aceto-carmine stains cell structures which are weakly acid in character (about pH 4-5) probably by precipitating as large dye aggregates. The technic appears to be highly specific for nucleoli and related cell bodies.