THE EFFECT OF PHOSPHOMOLYBDIC ACID ON THE STAINABILITY OF CONNECTIVE TISSUES BY VARIOUS DYES

Abstract

The mechanism of the selective staining of connective tissue obtained in trichrome methods (e.g. Masson, Heidenhain, Goldner) by "mordanting" with phosphomolybdic acid was investigated in sections of rat intestine. Information on the distribution of phosphomolybdic acid was obtained by treating sections with this acid and then with stannous chloride. The molybdenum blue thus obtained was located in those very structures which were stained selectively in trichrome methods. The chemical characteristics of the dyes taken up after phosphomolybdic acid treatment were investigated by comparing sections stained with acid, basic and amphoteric dyes. In the absence of phosphomolybdic acid, only dyes with acidic groups yielded a staining of connective tissue, but this staining was not selective. In sections pretreated with phosphomolybdic acid, only dyes with basic groups stained connective tissue, and only dyes with strong basic groups yielded a selective staining of these structures. Basic and amphoteric dyes applied after phosphomolybdic acid had the same distribution as this acid. It is concluded that the polyvalent phosphomolybdic acid is forming a bridge between the substrate and the dye, holding the dye and probably also the substrate by their cationic groups.