STAIN TECHNIQUE 17 



an acid retards the speed of staining, ammonium alum produces a 

 color more fast to washing, and the two together in the stain pro- 

 vide a better differentiation of minute cell structures. Basic dyes 

 have an affinity for tissues containing tannins, resins or fatty acids ; 

 for spores, lignified xylem, cellulose, fibers, and cork. The chroma- 

 tin and chromosomes are stained before the cytoplasm is affected. 



An unfamiliar basic dye is used for one minute. If the color is 

 too light, try one hour and then 24 hours. Whenever the color is 

 too dark at the end of one minute, leave the material in the stain 

 for five seconds. With two or three tests it is possible to approxi- 

 mate the time interval that gives the desired result. A clear color 

 is obtained with Rhodamine 6G in 12 to 24 hours, Safranine in 

 15 minutes to 24 hours, Methylene Green 15 to 30 minutes, New 

 Methylene Blue in five to ten minutes, and Methyl Violet in three 

 seconds to ten minutes. 



Nomenclature of dyes. Under the above system of classify- 

 ing the commercial dyes, a very convenient mode of indicating the 

 particular shade of dyestuff by a letter or number denotes: A, 

 extra concentrated, as in Safranine A ; B, blue, as in Niagara Sky 

 Blue 6B; D, direct, in Alkaline Green D; G, (gelb) yellow, as in 

 Pyronine 2G ; O, concentrated, in Safranine O ; R, red, an Acridine 

 Yellow R; S, (sauer) acid, as in Fuchsine S; X, concentrated, in 

 Safranine X; Y, yellow, as in Bismarck Brown Y; and the nu- 

 merals, I, II, III, in Orange I, Orange II, Orange III, and Orange 

 IV which indicate a series of shades of one color. 



