Detection of DNA in mammalian tissues following removal of RNA with cold phosphoric acid.

The paper deals with the staining of nuclei in mammalian tissue sections with night blue, belonging to diphenylnaphthylmethane group and is devoid of any primary amino group in its molecules but is provided with a secondary amino group and tertiary amino groups. Staining of the DNA-phosphate groups with an aqueous solution of night blue depends upon selective removal of RNA from formalin-fixed mammalian tissues by the use of cold concentrated phosphoric acid for 20 min or 75% phosphoric acid in the cold for 2 h. Moreover, sections from which RNA has been extracted can be hydrolysed in 6N HCl at room temperature for 15 min and then can be stained with the aqueous solution of the dye. Sections of tissues after only acid hydrolysis and staining also reveal very satisfactory staining of the nuclei. Possible mechanism of staining has been suggested.