88 Biological Stains 



position, it has similar physical properties and is fat soluble. Until 

 recently it has been regarded as one of the best fat stains known; 

 see, however, oil red O and oil red 4B, below, oil blue NA (p. 228) 

 and Sudan black B, (p. 98). 



For the technic of the Herxheimer stain for fat calling for the use of Sudan IV, 

 see Staining Procedures, p. ID3-I8. For Lillie's supersaturated isopropanol 

 technic, see p. ID3-2O. 



d8 oil red O 



As explained elsewhere, this dye has often been confused with 

 Sudan II. It is, however, quite different in composition, more 

 closely related to Sudan IV than to Sudan II. It consists of the 

 following together with its isomers having the methyl groups in 

 other positions: 



Oil red O was recommended by French (1926c) as a substitute 

 for Sudan III, to be preferred because of its greater depth of color. 

 Lillie (1944c) recommends it for this same reason, regarding it as 

 one of the best fat stains known to him. It may be employed in 

 the Herxheimer formula (an approximately 0.1% solution in equal 

 parts of acetone and 70% alcohol), in the pyridin formula of 

 Proescher (1927), or in Lillie's supersaturated isopropanol technic. 



For Proescher's oIl-red-0-pyridin technic, see Staining Procedures, p. ID3-I9. 



For Lillie's supersaturated isopropanol technic, see Staining Procedures, p. 

 ID3-2O. 



DlO OIL RED 4B 



This is a dye of uncertain composition which is rarely referred 

 to in the biological literature, but mentioned by Lillie (1944c) as 

 one of the best fat stains to employ in the supersaturated iso- 

 propanol technic. 



