Xanihene Dyes 187 



Fluorescein is a yellow dye of very low tinctorial power, and 

 hence of no value for ordinary staining purposes. It is on the 

 other hand extremely fluorescent, the greenish yellow fluorescence 

 being detectable in extremely high dilution. On account of this 

 latter property the dye is used to determine the possibility of con- 

 tamination from some suspected source getting into a neighboring 

 water supply. 



This fluorescence is even more pronounced in ultraviolet light, a 

 fact which makes the dye useful in fluorescence microscopy. Thus 

 Hercik (1939) employs it as a fluorochrome in the study of epi- 

 dermis cells of Allium; Levaditi et al. (1940) in virus studies; Met- 

 calf and Patton (1.944) in insect entomology. 



It has been included by Williams and Green (1935) in a series of 

 dyes that prove useful in media in which fungi are growing, the 

 absorption of the dye by the fungi giving characteristic colors to 

 the colonies. 



«« EOSIN Y (i.e., yellowish) c. I. NO. 768 



Synonyms: Eosiriy water soluble. Bromo acidy J, TS, XL or XX. 

 Bromofluorescein. Bronze bromo ES. 



Various shades denoted: Eosin B extra, BP, BS, DH, G, GGF, J 

 extra, SJ, JiJ, JJF, KS, S extra, Y extra and YS. 



This dye is typically tetrabromo fluorescein: 



Br Br 



NaO I I 



_Br 



'\/-c=\/ 



Br I 



i I COONa 



C2oH605Br4Na2; Mol. Wt. 691.906 

 {An acid dye; absorption maximum 515-518) 

 Solubility at 26°C: in water U-20%; in alcohol 2.18% 



but the mono- and dibromo derivatives are also known and fre- 

 quently occur in eosin. This affects the shade, as the more bro- 

 mine present the redder the dye. It is plain that various mixtures 

 of these compounds are on the market; but it has not yet been de- 

 termined which are more suitable for biological purposes. Con- 

 siderably more work on eosin is needed than has been done at the 

 present time. From the name "water soluble eosin'* it is often 



