324 on AFTER XXVI. 



648. Chromatin Stains. — For fresh tissues see § 645. 



For sections of liardened tissues, stains should be chosen 

 amongst those that give a very intense as well as a very 

 shai-p coloration. Some years ago safranin and gentian 

 violet were the most used. At the present time their place 

 has been taken by the iron hsematoxylin of Benda or Heid- 

 ENHAiN. An alum hasmatoxylin such as ivell-ripened Dela- 

 field's, or Ehrlich's, or hsemalum, may also give very good 

 results. 



See also Thionin, Kernschwarz, and Iron Carmine, § 220. 

 For Bataillon and KoEHLEE'sborax-metliylen-blue see Compfes 

 Rendus, cxvii, 1893, p. 521. 



649. Nucleoli are " acidophilous " in so far as, in fixed 

 material, they select the acid dye or dyes from mixtures such 

 as the Ehrlich-Biondi stain. With this they stain mostly 

 red, sometimes orange. With /res/i material they do not stain 

 at all with acid methyl green (distinction from chromatin). 



But in fixed material treated with basic dyes (safranin, 

 gentian, etc.) by the regressive method they stain more 

 energetically than resting chromatin, and at least as much 

 so as chromatin in the kinetic state. With iron-htematoxylin 

 they stain sometimes full black, sometimes grey with a black 

 shell. 



They can frequently be well demonstrated in unstained 

 preparations examined in water, being brought out by their 

 superior refractivity, and are sometimes visible in the living 

 cell. 



One of the best ways of demonstrating them is to fix with 

 strong liquid of Flemming, and stain with safranin, followed 

 by differentiation with acid alcohol (§ 286). 



Obst (Zeit. wiss. Zool., Ixvi, 1899) fixes in sublimate, stains 

 in borax carmine, and then stains the sections for three 

 hours in very dilute aqueous methyl green or solid green. 

 Nucleoli blue, chromatin red. 



BucHNEE [Arch. Zellforsch., iii, 1909, p. 337) has found 

 this useful for distinguishing the accessory chromosome in 

 testis cells of Orthoptera — normal chromosomes red, accessory 

 and chromatin nucleoli blue-violet. 



ZiMMERMANN (Zfiit. wiss. Milc, 1896, p. 463) stains for 10 

 minutes in a fresh mixture of 9 parts O'l per cent, aqueous 



