CHAPTER XIII* 

 STAINING 



233. Dyes. It is hardly the place in such a book as this to go 

 at all deeply into the subject of dye chemistry. There are, 

 nevertheless, certain rather fundamental principles in connection 

 with chemistry which are often useful for the biologist to bear in 

 mind when he is considering what dyes to select for any particular 

 staining procedure. A few of these most fundamental principles 

 of dye chemistry will be discussed here. For more detailed 

 information the reader is referred to Conn (" Biological Stains," 

 3rd ed., Geneva, N.Y., 1936). 



From the standpoint of the biologist, dyes may be classified as 

 follows : — 



A. Simple dyes. 



(1) Artificial dyes. 



(a) The nitro dyes {e.g. picric acid). 



(b) The azo dyes {e.g. orange G, Bordeaux red, the 



Sudans, Bismarck brown and Congo red). 



(c) The oxyquinone dyes {e.g. alizarin). 



{d) The quinone-imide dyes {e.g. thionin, methylen blue, 



the azures, toluidine blue, neutral red and the 



safranins). 

 {e) The phenyl methane dyes {e.g. brilliant green, light 



green, the fuchsins and methyl violets, methyl 



green and the anilin blues), 

 (/) The xanthene dyes {e.g. the pyronins, eosin, ery- 



throsin, phloxine and rose Bengal), 



(2) The natural dyes. 



(a) Logwood and brazilwood derivatives. 

 {})) Cochineal derivatives. 



(c) Miscellaneous {e.g. safranin, indigo, orcein and 

 litmus). 



B. Neutral stains or compound dyes {e.g. the Romanovsky 

 blood stain and its various modifications). 



Dyes of any of the above groups except the last may be either 

 acidic or basic, these two terms indicating, as explained below, 

 not the reaction of the dye, but whether the dye property is 

 carried by the anion or the cation. For practical purposes it is 

 often niore necessary to know whether a dye is acidic or basic 



* By H. J, C. 



124 



