The Effect of pH on Staining by Eosins

The effect of pH on staining by 7 dyes of the eosin group was studied by means of specimens fixed 12-18 hr in Gilson's, in Petrunkewitsch's, or in Zenker's fluids, respectively. Sections were soaked in water or alcohol, depending upon the stain solvent, adjusted in 31 equal steps from pH 4.0 to 10.0 before being stained in similarly adjusted dye solutions. The stained sections were rinsed at H-ion concentrations identical to that at which staining took place, until no further color came away, and mounted. Variations in pH elicited different degrees of stain retention; different fixation altered staining affinity even though staining was effected at identical pH values.