30 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



6. A niline gentian violet, which is prepared as follows : 



First prepare aniline oil water by shaking water (preferably dis- 

 tilled) with more aniline oil than it will dissolve ; a milky 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. 



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. 



9. 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 

 placed. A filter-paper is kept permanently in this funnel, and the 

 stain is filtered directly on to the slide or cover-glass. 



Gram's iodine solution may be mentioned here, though it is not a 

 stain. It consists of a solution of iodine, i part ; iodide of potassium, 

 2 parts ; water, 300 parts. It keeps indefinitely. 



