STAINS 31 



emulsion will result, and this must be allowed to settle for a short 

 time. Then filter it through a double thickness of filter-paper 

 which has been previously moistened with water. This must be 

 prepared fresh, and as a small amount is often required in a hurry, 

 the following method is frequently most useful : Put about 

 J inch of aniline in a test-tube, and half fill the latter with dis- 

 tilled water. Boil for half a minute, then cool under the tap. 

 When quite cool, filter. 



To 9 parts of the solution thus obtained add i part of saturated 

 solution of gentian violet in alcohol. 



This solution keeps badly, and it is necessary that it should be 

 freshly prepared, as very important inferences are drawn from 

 results obtained with it. The following keeps better, and answers 

 every purpose. 



Carbolic Gentian Violet (a substitute for aniline gentian violet). — 

 Add I part of saturated alcoholic solution of gentian violet to 

 9 parts of a I in 20 carbolic lotion.* 



7. Carbol thionin is made by adding i gramme of thionin to 

 100 c.c. of a I in 40 solution of carbolic acid. 



This stain keeps fairly well, but it must always be filtered 

 immediately before use, as crystals which may have a most 

 delusive resemblance to long slender bacilli are frequently de- 

 posited in it. A similar formation of crystals also occurs if the 

 stain be allowed to dry on the slide. 



In cold weather the thionin may crystallize nearly completely 

 out, and the fluid stain very badly. If kept in a warm place for 

 a few hours it will recover its properties, the sediment being 

 redissolved. 



8. Eosin is used in a 4 or 5 per cent, watery solution. This 

 keeps well. Red ink (slightly diluted) will answer most purposes. 



g. Acid, methylene blue is prepared by mixing 2 parts of borax 

 methylene blue [vide supra), i part of glacial acetic acid, and 

 7 parts of water. It is only used for staining cells, casts, etc., in 

 wet preparations, and has the advantage of dissolving the red 

 blood-corpuscles, which when numerous often obstruct the view 

 of the more important elements. It keeps well. 



Stains should be filtered before use. Where much work is to 

 be done, it is convenient to keep them in bottles which are closed 

 with a perforated cork through which a small glass funnel is 



* It sometimes precipitates immediately after being made, for no apparent 

 cause. Should this not happen it usually keeps for months. 



