232 Biological Stains 



the dye has now come to have a distinct recognition as a fluoro- 

 chrome. Thus Richards (1943) employs it in the demonstration 

 of the potato scab organism by ultraviolet light. 



3. QUINOLINE DYES 



Of the quinoline dyes only the following is of interest to bi- 

 ologists: 



c5 PINACYANOL C. I. NO. 8o8 



Synonym: Sensiiol red. 



/ U -I \ 



I / I I \ I 



~\ / \ r 



CHj CH,— N-=CH CH CH- =N— CH^ . CHj 



\ 

 I 



C25H25N2I; Mo^. WL 480.386 

 {A basic dye; absorption maxima [526 ^ 563] 608 in alcohol) 



This dye is used primarily for color sensitization in photography, 

 but has been employed by Proescher (1933) for staining frozen 

 sections, and by Hetherington (1936) as a supra-vital stain for 

 mitachondria in blood. It has been employed in combatting 

 streptoccoci. S. H. Bensley (1952) has prepared a neutral stain 

 from it (an erythrosinate) and uses it for staining mast cells. 



Another quinoline dye mentioned in biological literature is: 

 Quinoline yellowy C. I. No. 801. 



4. DIAZONIUM AND TETRAZONIUM SALTS 



Histochemistry has brought into microscopic use certain com- 

 pounds which are not dyes. Some of the histochemical reagents, 

 like basic fuchsin, are dyes used in decolorized state, and are dis- 

 cussed elsewhere in this book; others, like the oxidizing agents 

 periodic acid and tetra-acetic acid, are simple chemicals hardly 

 calling for special consideration. There are, however, certain im- 

 portant histochemical reagents which are so closely related to 

 dyestufls that they can hardly be omitted from these pages. They 

 are especially the diazonium, tetrazonium and tetrazolium salts. 



The diazonium and tetrazonium salts have the same basic struc- 

 ture, and are considered in this section. They are salts of a 

 theoretical base having the structure R-N = N— OH [or 

 R-N(OH) = N]. Not only the base thus indicated, but its simple 



