Gross Demonstration of the Mammalian Atrioventricular Bundle by A Periodic Acid-Schiff Procedure

The following procedure stains the atrioventricular conduction system selectively. (1) Wash the fresh heart with physiological saline solution to free it of blood; (2) fix it in 10% formalin containing 0.5% HIO₄ for 1 hr; (3) wash in 3 changes of distilled water for 20 min; (4) keep in 80% alcohol for 12 hr to 2 wk; (5) wash with distilled water; (6) treat with a dilute Schiff's reagent containing 0.1 gm of basic fuchsin per 100 ml for 0.5-2 min; (7) rinse in three changes of 2% Na₂SO₃ in 0.2 N HCI for 3-5 min; (8) wash and examine in 80% alcohol; store in 80% alcohol.