The histochemical versatility of Sudan Black B.

Sudan Black B (SBB) is perhaps the most popular of all Sudan dyes yet its use in lipid histochemistry is severely limited. Not only does it fail to stain crystalline lipids but others such as some phospholipids and free fatty acids tend to dissolve in the dye solution. Lipids are less soluble after prolonged fixation in the presence of calcium, but calcium is ineffective in the short term. Bromine is a more successful lipid stabiliser and furthermore, after bromination cholesterol crystals become sudanophilic. Bromine-SBB, therefore, is a simple sensitive method for the detection of all lipids. With bromine the range of SBB staining can be extended to situations other than conventional fat staining; for example as a permanent stain in lipid chromatography. Bromine-SBB can also be used to demonstrate phospholipids selectively when all other lipids are extracted with acetone. The relationship between lipid distribution and certain metabolic functions of associated cells can be revealed simultaneously if enzyme histochemical procedures are followed by SBB and a suitable nuclear counterstain.