STAINING. 161 



Formaldehyde : see OHLMACHER'S process. 



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

 to the beginner for general work : For sections, MAYER'S 

 h&malum ; or, for chromosmium objects more especially, 

 BENDA'S or HEIDEN MAIN'S iron haematoxylin. 



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

 or Mayer's carmalum, or haemalum, unless the object be so 

 impermeable as to require a more highly alcoholised stain, in 

 which case take Mayer's par acar mine, or for chromic acid 

 objects Mayer's hasmacalcium. 



For fresh tissues or small entire objects, methyl green, if it 

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

 take carmalum or alum-carmine (but both of these may give 

 precipitates with marine animals). 



Picric acid may be used for double-staining in bulk after 

 carmine or haematoxylin. 



The beginner will probably do well not to use a double stain 

 where a single one will do. To do so is too often to go farther 

 and fare worse. 



204. Staining Reagents and Chemicals. You are not likely 

 to succeed in staining, especially in 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 trustworthy house for chemical pro- 

 ducts at all events, not in the case of coal-tar colours. It 

 is not sufficient that these should be what they are com- 

 mercially described to be ; they may be pure, and yet not 

 give good stains. They must (in the case of coal-tar colours, 

 at all events) be the identical products used in their work by 

 the authors who have described and recommended them (see 

 the note on the numerous safranins in the market, sub voce 

 Safranin) . I therefore feel constrained to advise everybody 

 to get his reagents at all events his anilins from the well- 

 known chemists GRUBLER & HOLLBORN or MUNDER. Griibler 

 & Hollborn have all the tried reagents in stock, and supply 

 only such as have been found by experiment with tissues to 

 furnish the desired stain. They also make up fixing and 

 staining solutions, injection and imbedding masses, etc., 

 according to the classical formulae, and send them out neatly 



11 



