Polyoxyethylene Sorbitan Monopalmitate (Tween 40) as a Vehicle for oil Red O Fat Stain

An oil red O fat stain is prepared by dissolving 250 mg of the dye in 100 ml of a 1% Tween 40 solution in 30% alcohol, and incubating the mixture at 60°C for 24 hr. The solution is then filtered at room temperature under vacuum through medium porosity frittedglass. Frozen sections cut from material fixed in CaCl2-CdCl2-formalin (1%:1%:10%) are placed in the stain for not less than 4 hr. After washing in the alcoholic-Tween solvent, they are mounted on glass slides from distilled water with Farrants' medium. The resulting preparations appear to be permanent, for in a 2-yr test they have remained free from stain crystalization and the fat particles are still discrete and dark red.