Xanthene Dyes 197 



r36 rose bengal C. I. NO. 779 



Various shades denoted: Rose bengal extra^ SB Conc.y N extra^ DYy 

 B and 2B. 



I I 



NaO I I 



o_/\=o 



C1~\/~C1 



I 



CI 

 C2oH205l4Cl4Na2; Mol. Wt. 1017.718 

 (An acid dye; absorption maximum S^^^^^-S) 

 Solubility at 26°C: in water 36.25%; in alcohol 7.53% 



The dye has a pleasing deep pink color; and although an acid 

 dye it proves to have considerable affinity for bacterial protoplasm, 

 and to have good selective properties when used as a bacterial 

 stain. It has been recommended (Conn 1918, 1921) for staining 

 bacteria, especially in soil suspensions. It has also been used as a 

 cytoplasm stain following hematoxylin or preceding toluidine blue. 

 Maneval (1934!) employed it in the negative staining of bacteria 

 and Ono (1934) for spirochaetes in blood. It also finds use in 

 Delprat and Stowe's test (1931) for liver function. Popper (see 

 Metcalf and Patton, 1944) mentions it as a useful fluorochrome in 

 the study of fats under ultraviolet illumination. Smith and Daw- 

 son (1944) employ this dye as a bacteriostatic agent in media de- 

 signed to permit the growth of soil fungi while repressing the 

 bacteria; this is the only instance yet noted of one of the fluoran 

 derivatives being thus used. 



From Fig. 25, in which the spectral curve of this dye and phlox- 

 ine B are compared, it will be seen that they differ more in shape 

 than in the position of the absorption maximum. 



For technic of general staining of pure cultures of bacteria, see Staining Pro- 

 cedures, p. IIIA2-5. 



For technic of Conn's stain for bacteria in soil, see Staining Procedures, P.IIIA2- 

 21. 



4. PHENOLPHTHALEIN AND THE SULFONPHTHALEINS 



A phthalein is a compound of phthalic acid : 



COOH 



COOH 



