Application of the Periodic Acid-Schiff Technique to Whole Chick Embryos

The practicability of applying histochemical reactions to bulk staining has been explored by subjecting whole chick embryos at early stages to the periodic acid-Schiff (PAS) reaction. A comparison of the microscopic distribution of PAS positive substances revealed by this procedure with that obtained by the standard routine, i.e., staining of deparaffinized sections on slides, has shown similar localizations of PAS positive material and, in addition, finer morphological detail and more intensive reactions by staining the specimens in toto. The following method is recommended for chick embryos between stages 11-17 (Hamburger and Hamilton): Fixation in Gendre's fluid at 4°C; oxidation with alcoholic buffered periodic acid, 15 min; rinsing in distilled water, 10 min; Schift's reagent, 30 min; 3 sulfite rinses, 5 min each; running tap water, 10 min; dehydration, clearing and double-embedding in celloidin and paraffin.