CHOICE OF STAIN. 53 



solution of iodine in 1 per cent, solution of iodide of potassium 

 (ARNSTEIN, Anat. Anzeiger, ii, 1887, p. 125; Zeit. f. wiss.Mik., 

 iv, 1, 1887, p. 85), or with picro-carmine, or with picrate of 

 ammonia (Anat. Anzeig., 1887, p. 551), and mounting in 

 glycerin. Bismarck brown stains may be fixed with 0'2 per 

 cent, chromic acid, and the preparations may be stained with 

 safranin, care being taken not to expose them too long to the 

 action of alcohol. 



I may say that personally I have found gentian, dahlia, and 

 methylen blue, added to indifferent liquids, extremely useful 

 in the examination of tissue-cells. Quinolein and Bismarck 

 brown are well-known aids to the study of Infusoria. Methy- 

 len blue has a specific affinity for sensitive nerves (see post, 

 127, and Part II). 



94. Choice of a Stain. The following may be recommended 

 with confidence for general work : For sections, Flemming's 

 method, with safranin or gentian for a single stain (see Nos. 

 102, 103), and gentian followed by eosin for a double stain. 



For staining in toto, Grenacher's alcoholic borax-carmine 

 (No. 163), unless the object be so impermeable as to require a 

 more highly alcoholised stain, in which case take Mayer's 

 alcoholic carmine (No. 164), or Mayer's cochineal tincture 

 (No. 168), or, for chromic-acid objects, Kleinenberg's haema- 

 toxylin (No. 184). 



For fresh dissociated tissues or small entire objects, methyl 

 green, if it is not important to have permanent preparations ; 

 if it is, take alum-carmine or picro-carmine. 



Picric acid may be used for double-staining after carmine 

 or haematoxylin. 



Many others of the numerous stains discussed in the follow- 

 ing chapters render most valuable services, and will be found 

 recommended in the special paragraphs as occasion dictates. 



I would add one word of advice to the beginner : Never use 

 a double stain where a single one will do. To do so is too 

 often to go farther and fare worse. 



And a word of caution to beginners and others : 



You are not likely to succeed in staining, especially in the 

 beautiful processes of staining with coal-tar colours, unless 

 you see to it that you are working with chemicals of the proper 

 quality. You cannot ensure this by going to a generally trust- 



