EFFECTS OF WASHING ON POSITIVE STAINING

When sections embedded in epoxy resin were conventionally stained with lead citrate and washed very briefly, about 1 sec, a very high staining intensity was attained. However, the staining intensity was quickly reduced by washing 10 min. When uranyl acetate-stained sections were washed for 1 sec, a much lower intensity was obtained. Nevertheless, a significant reduction in staining intensity occurred when washing was prolonged to 10 min. These observations indicated that not only in staining of frozen sections or sections embedded in hydrophilic resins but also those embedded in more hydrophobic resins, the staining intensity is closely related to the degree of washing, particularly in lead-staining.