Apparatus (10) for the automatic staining of tissue includes a body (12) on which a carousel (16) rotates. The carousel (16) is able to carry a number of slides (24) bearing tissue samples. A delivery head assembly (18) is mounted on the body (12) for movement across the diameter of the carousel (16). The head assembly contains a clear nozzle (20) and a spray nozzle (22). A version (50) of the spray nozzle (22) for spraying a fluid biochemical agent onto a slide (24) has a main body (52) a plug (56) in the main body (52) and a cap (54) on the main body (52) between which there is a swirl chamber (68) into which fluid passes from the body (52). The fluid enters the swirl chamber (68) such that flow in the chamber (68) is concentric to the chamber axis and thereafter flows from the body (52) through an exit ( 66), thus minimising damage to the biochemical agent.