STAINING SOLUTIONS 137 



Alkalis. Caustic potash, ammonia, sodium borate, ammonium carbonate, and certain 

 organic alkalis (aniline, phenylamine, toluidine). 



Mixtures of two dyes, of which one acts as a mordant towards the other. 



Action of heat. The rapidity and depth of the staining can be increased 

 by heating the preparation in a bath of the stain to 60 or 100 C. 



1. Staining- solutions. 



The staining solutions used in bacteriology are very numerous. Every 

 observer has his own preferences, so that there is a multiplicity of formulae, 

 making the subject very complicated and embarrassing for the beginner and 

 practical work would gain much by a reduction and simplification of these 

 staining processes. As a matter of fact a few formulae will meet all ordinary 

 requirements, and if these be thoroughly understood errors which often arise 

 from the use of too complicated and unfamiliar methods will be avoided. 



The various formulae to be found in papers published during recent years must 

 be given, but those methods which in our own experience have given good results 

 will be distinctly indicated and will be found sufficient for practically all purposes. 

 The acid dyes will not be dealt with in this chapter but will be referred to later, 

 and the consideration of some of the staining methods of limited application will 

 be deferred until occasion for their use arises. 



To avoid mistakes only good dyes obtained from well-known sources 

 should be used. 



A. Simple solutions. 



These solutions have only a limited use ; staining solutions containing a 

 mordant are generally better. 



(i) Alcoholic solutions. 



Alcoholic solutions of the basic aniline dyes are prepared by mixing in a 

 ground-glass stoppered bottle : 



Dye, - 1 gram. 



Absolute alcohol, - - 10 c.c. 



Shake well and leave the alcohol standing on the dye. Filter before use. 

 Alcoholic solutions keep for a very long time in the dark, and solutions of the 

 following dyes should be kept in the laboratory, viz. fuchsin, crystal- violet 

 or gentian-violet, and methylene blue. 



These solutions are not used for staining, but when diluted with water 

 serve for the preparation of watery alcoholic solutions. 



(ii) Watery alcoholic solutions. 

 Watery alcoholic solutions are prepared by mixing 



Filtered alcoholic solution of the dye, - 1 to 5 c.c. 



Distilled water, - 100 c.c. 



Filter immediately before use. 



These solutions are seldom used in this form, as they do not keep well : 

 it is simpler to make them up as required by pouring several cubic centimetres 

 of water into a porcelain dish, and adding to it a few drops of the filtered 

 alcoholic solution until an iridescent pellicle with a metallic lustre appears 

 covering the surface. 



(iii) Aqueous solutions. 

 Mix in a small bottle 



Dye, - 0'25 gram. 



Distilled water, 25 c.c. 



Shake and leave the water standing on the dye. Filter before use. 



