96 Microscopic Histochemistry 



histological purposes (Sudan III and IV; Sudan black B;^^* ^* 

 Oil red O;^' Blue B.Z.L.;^^ Nile blue; etc.). With the excep- 

 tion of Sudan black B, which is an excellent stain for phos- 

 phatides, all the dyes mentioned stain triglycerides and fatty 

 acids in a much darker shade than phospholipids. The latter 

 may actually remain practically unstained. According to 

 Gerard,^^ Sudan black B can be used to differentiate between 

 petrolatum and animal lipids. The former will stain in a clear 

 violet, the latter blue-black. 



Oil dyes (with the exception of Nile blue) are usually 

 made up in alcohol ( 50-70 per cent ) or some similar solvent, 

 such as ethylene or propylene glycoP^' ^^ or pyridine.^^ Solu- 

 tions in 70 per cent alcohol stain fast, but they may remove 

 some of the lipid. Lower concentrations of alcohol are safer, 

 but their solvent power for the dyes is lower, and optimal 

 staining time is greatly prolonged. Solutions in glycols are 

 reported to be safe and fast in action; ^^ however, in view of 

 the known solvent power of glycols (especially of propylene 

 glycol) for many water-insoluble organic substances, the 

 method should be re-examined critically. Sixty per cent iso- 

 propyl alcohol -^ and 50 per cent diacetin-^ have also been 

 recommended as solvents. 



The writer finds that one of the good solvents for oil dyes 

 is 60 per cent triethylphosphate. It is entirely harmless to 

 lipids, and the staining power of the solution is not much 

 inferior to that of alcohohc solutions. In addition, the loW 

 volatihty of triethylphosphate prevents the precipitation of 



13. Lison, L.: Compt. rend. Soc. de biol., 115:202, 1934. 



14. Lison, L., and Dagnelie, J.: Bull, d'histol. appliq. a la physiol., 12:85, 

 1935. 



15. Lillie, R. D.: Stain Technol., 19:55, 1944. 



16. Gerard, P.: Bull, d'histol. appliq. a la physiol., 12:92, 1935. 



17. Hartman, T. L.: Stain Technol., 15:23, 1940. 



18. Chiffelle, T. L., and Putt, F. A.: Stain Technol., 26:51, 1951. 



19. Proescher, F.: Stain Technol., 2:60, 1927. 



20. LilHe, R. D., and Ashbum, L. L.: Arch. Path., 36:432, 1943. 



21. Gross, W.: Ztschr. f. wissensch. Mikr., 47:64, 1930. 



