EOsiN, Y (i.e., yellowish) C. I. NO. 768 



Synonyms: Water soluble eosin. Eosin W or WS. 



Various shades denoted: Eosin G, Y extra, S extra, J extra, 

 B extra, GGF, 3J, 4J, KS, DH and JJF. 



{An acid dye; absorption maximum about 516.) 



This dye is typically tetrabrom fluorescein : 



Br Br 



NaO 



COONa 



but the mono- and di-brom derivatives are also known and fre- 

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

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

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

 mined which are more suitable for biological purposes. Consider- 

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

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

 assumed that this dye is not soluble in alcohol. This is not true, 

 however. 



Yellowish eosin is one of the most valuable plasma stains known. 

 It is used in various technics for staining the oxyphile granules of 

 cells (i.e., the granules having special affinity for acid dyes); these 

 cell elements, in fact, being often called eosinophile granules be- 

 cause their presence was first recognized thru the use of this dye. 

 It is often employed as a counterstain for haematoxylin and the 

 green or blue basic dyes; as for example by Mallory with methy- 

 lene blue,* and by List with methyl green. It is used by Mann 

 mixed with methylene blue as a tissue stain; and by Teichmuller 

 for staining sputum before staining with methylene blue. At the 

 present time one of the uses for which it is in greatest demand is 

 as a blood stain in the technic of Romanovsky, with its various 

 modifications, in which it is combined with methylene blue to 

 form a "neutral" stain. 



METHYL EOSIN C. I. NO. 769 



Synonym: Eosin, alcohol soluble. 



This is the methyl ester of yellowish eosin, the sodium salt of 

 which is: 



*See, however, the statement about this technic below under phloxine (p. 82) 



79 



