64 LABORATORY BACTERIOLOGY 



Tannic acid solution should be freshly prepared, but the 

 iron sulphate solution is better if it stands until it begins to turn 

 brownish by oxidation, but it should not be too old. If when 

 this mordant is used it gives a precipitate, filter again. When 

 properly prepared it should have much the same color as a 

 solution of hematoxylin. 



loeffler's stain (ziehl's carbol fuchsin) 



Saturated alcoholic solution basic fuchsin . 2.5 cc. 



Five per cent carbolic acid . . 20 cc. 



If not clear, add fuchsin solution drop by drop until it clears, 

 then filter. 



pitfield's mordant 



Ten per cent aqueous solution tannic acid 10 cc. 



Saturated aqueous solution mercuric chloride , 5 cc. 



Saturated aqueous solution potassium alum 5 cc. 



Ziehl's carbol fuchsin . . 5 cc. 



Mix, let stand two or more hours, and decant clear fluid or 

 filter. 



pitfield's stain 



Saturated aqueous solution potassium alum lo cc. 



Saturated alcoholic solution gentian violet 2 cc. 



Mix, let stand two or more hours, and filter. 



Saturated alcoholic solution of methyl violet, basic fuchsin, 

 or methylene blue can be substituted for gentian violet in the 

 above formula with equally good results. 



With a pipette apply to a film all the mordant the cover glass 

 will hold, allow it to act two or three minutes without heating, 

 and rinse thoroughly in clean water ; apply the stain in the same 

 manner, allow it to act two or three minutes without heating, 

 rinse well, and examine in water, or dry and mount in balsam. 



All these solutions should be freshly prepared. Consider- 

 able care in washing after the mordant will be well repaid by 

 insuring a cleaner background. 



