140 Biological Stains 



Auramine O has been in use for some time as a drug, but until 

 recently has been regarded as having httle value in microscopic 

 technic. A search of the literature in 1936 revealed only the 

 following rather obscure staining procedures calling for this dye: 

 by Vinassa (1891) for staining plant sections; by Fischel (1901) 

 for vital staining of salamander larvae; and by Kisser (1931), with 

 cresyl violet as a tissue stain. More recently, however, its pro- 

 perties as a fluorochrome have brought it into considerable promi- 

 nence in fluorescence microscopy. Richards and Miller (1941) 

 recommend it as the best, among numerous fluorochromes investi- 

 gated by them, for staining the tubercle organism. Their method, 

 because of the low magnification and large fields which it makes 

 possible, allows such an increase in the number of positives in 

 diagnosis that it has attracted much attention to this dye since 

 their method appeared. 



The spectrophotometric curve of a typical sample is given in 

 Fig. 17. The most striking feature of this curve is the secondary 

 maximum at 380. 



For technic of fluorescent staining of acid-fast bacteria, see Staining Procedures,* 

 p. IIIA2-9. 



2. TRI-PHENYL METHANE DERIVATIVES 



There are two groups of tri-phenyl methanes to concern us, the 

 amino and the hydroxy derivatives. The former, which are much 

 the more numerous, are very strongly basic, thanks to the amino 

 groups, unless sulfonated like light green or acid fuchsin. The 

 rosolic acid dyes, on the other hand, are hydroxy phenyl methanes, 

 the amino groups being replaced by hydroxyl groups; they are 

 therefore acid instead of basic dyes. 



There are likewise two subdivisions of the amino derivatives, 

 the di-amino tri-phenyl methanes and the tri-amino tri-phenyl 

 methanes. These two groups are derivatives respectively of: 

 di-amino tri-phenyl methane 



H2N. 



H2N 



and tri-amino tri-phenyl methane, or paraleucanilin. 



H2N_/-\ n 



C 



*Conn and Darrow (1943-4). 



