Triple immunohistochemical staining for bromode - oxyuridine and catecholamine biosynthetic enzymes

A cap for a tubular fitting featuring a tubular body adapted to fit loosely over the exterior of a tubular fluid fitting and an interior surface inside the tubular body for bearing against a mating exterior surface on the fitting, the tubular body being retained either in a loose breathing position over the tubular fitting or in a sealing position with the mating interior and exterior surfaces tightly engaged. Releasable retaining means are provided to retain the body in either the breathing or sealing position and twisting means are provided to move the cap from one position to the other.