Methylene blue and azure-2 as stains for lipid in osmium-fixed tissues embedded in araldite.

Mixtures of methylene blue and azure-2 are stated to stain neutral lipid droplets an intense dark blue in 0-5-10 ,um-thick Araldite sections of osmiumfixed kidney (Muehrcke, Mandal, Volini, and Epstein, 1969; Tobian, Ishii, and Duke, 1969). Neither group of investigators, however, detail either the composition of the stain or the method. A modification of the methylene blue-azure-2 method of Richardson, Jarret, and Finke (1960) is used in this laboratory for general staining 0-5-1 0 ,m-thick Araldite sections of osmium-fixed tissue. With this technique, droplets, known to be lipid, are virtually colourless or a pale green. The present note describes in detail a method of using methylene blue and azure-2 to produce an intense blue-black colouration of lipid droplets.