COLORING AGENTS. 57 



NIGROSIN. 



[Errera recommends ' this tar derivative for 

 staining the nucleus. It is soluble in water, but 

 insoluble in alcohol and ether. After remaining a 

 short time in a solution of nigrosin, the section is 

 transferred to water, where it remains until no 

 more of the color is removed, when it may be 

 mounted in glycerine or glycerine jelly, or trans- 

 ferred to alcohol, and afterward cleared in oil of 

 cloves and mounted in balsam. The latter me- 

 dium serves best for specimens intended to show 

 the chromatin ; while the former are preferable 

 for those intended to show the achromatin of 

 Flemming. W. T.] 



EOSIN. 



This beautiful rose-colored derivative of phthalic 

 acid has a pronounced green fluorescence. It is 

 employed in aqueous [or alcoholic] solution. 

 Even a very small quantity has great coloring 

 capacity. 2 It has been used for staining Sarcina 

 and Sarcinoglobulus. It does not appear adapted 

 for use on bacteria (Bacillus, Bacterium, etc.). [I 

 have succeeded in obtaining fair preparations of 

 Bacillus subtilis by staining in alcohol-eosin, and 



1 Proces-verbal de la s6ance mensuelle du 25 Juin, 1881, Soc. beige de 

 Microscopic, p. CXXXIV. 



2 Poulsen : Om nogle mikroskopiske Planteorganismer. Nat. Foren. 

 viclsk. Meddel., 1879-80, p. 235. Preparations stained with eosin may be 

 preserved in glycerine. 



