Abstract
Aqueous 0.1% neutral red adjusted to pH 6.5, or mixed 1:1 with seawater, produced conspicuous fluorescence in plant and animal fats while acting as a conventional stain for acidic groups including volutin. The water-soluble, nonfluorescent dye predominating in acid solutions became deprotonized, lipophilic and fluorescent under neutral and alkaline conditions. Neutral dye crystals fluoresced dull red, whereas the fluorescence was either bright lemon yellow or blue-green in lipids, apparently dependent upon their composition.