Abstract
The use of alcoholic solutions of periodic acid does not greatly impair the periodic acid Schiff reaction of collagen. The Hotchkiss acidulated thiosulfate "reducing rinse" is essentially a sulfurous acid bath and acts to block aldehydes from coloring with Schiff reagent. As with deliberate sulfurous acid blockade procedures, prolongation of the exposure to Schiff reagent overcomes this blockade. Brief treatment with iodine and thiosulfate breaks this blockade just as it does that with bisulfite. Prolonged exposure to postassium bichromate solution creates weak diffuse aldehyde reactions in tissues, and also tends to weaken the reactivity of collagen to the periodic acid Schiff procedure.