The shade differs according to the proportion of these compounds 

 present, the red being deeper according to the proportion of the 

 tri-methyl compound in the mixture. The type safranin O, which 

 proves best for ordinary biological purposes, can be defined as 

 having its absorption maximum at 515///i. 



Safranin O is one of the most important nuclear stains knowTi to 

 the histologist. The botanist finds it especially valuable, as it 

 brings out lignified and cutinized tissues in vascular plants, and 

 can be employed in combination with a variety of contrast stains; 

 it is valuable as a protein stain in plants, and can be used to stain 

 spore coats. The cytologist makes use of it in the Benda technic 

 to stain chromatin in combination with light green as a contrast 

 stain; and even more widely in the Flemming triple stain, in which 

 it is employed as a chromatin stain, together with gentian violet 

 and orange G. The bacteriologist has some use for it, especially 

 as a counterstain in the Gram technic (see p. 68). 



AMETHYST VIOLET C. I. NO. 847 



Synonyms : Heliotrope B, Iris violet. 

 This dye is tetra-ethyl pheno-saf ranin : 



/\ N_/\ 



CH3CH. [ I II CH.CH3 



\ /\/~N=-\/\ / 



N / \ N 



/ /\ CI \ 



CH.CH, I I CH3CH2 



{A basic dye; absorption maxima about 589, [5Ji.5.5] ) 



Amethyst violet has been used by Ehrlich and Lazarus as a basic 

 dye in certain triple staining technics. 



A further dye of this group which the biologist must take into 

 account, altho it seems to have no significance as a stain, is methy- 

 lene violet RRA or 3RA, C. I. No. 842 {sy n. : fuchsin or safranin 

 extra blue.) This dye is a di-methyl safranin in which the methyl 

 groups are introduced into one of the amino groups instead of 

 directly into the benzene ring. It has no connection with the 

 methylene violet of Bernthsen, which is one of the constituents of 

 polychrome methylene blue; see p. 49. 



MAGDALA RED C. I. NO. 857 



Synonyms: Naphthaline red, naphthaline pink, naphthylamine 



pink, Sudan red. 



This is a naphtho-saf ranin, and is a mixture of the monamino 

 and diamino compounds: 



56 



