Abstract
Several fluorochromes were used to stains directly R. mooseri in smears and tissues. The effects of fixatives, hydrogen ion concentration, time in stain and concentration of stain were studied also. Interference by background fluoresence was minimized by a preliminary staining of fixed preparations with an alcian blue, periodic acid-Schiff sequence. Maximum fluorescence of rickettsiae was obtained when tissues were fixed in Carnoy's or smears in methanol or absolute ethanol-chloroform (1:1) and stained with acridine orange.