METHODS OF STAINING. 309 



of the stain is reduced by the use of alcohol, 95 per cent, or abso- 

 lute, which bleaches the portions of the specimen which retain the 

 color with the least tenacity. If" the action of the alcohol be main- 

 tained for too long a time, the color may be discharged from all 

 parts of the specimen. The method of overstaining a specimen, 

 and then discharging the color from those parts where it is not de- 

 sired, is a common one. The process of discharging the color is 

 called the " differentiation " of the stain, because it serves to dis- 

 tinguish those elements which hold the color strongly from those- 

 which part with it easily. 



8. Carbol-fuchsin. — 



Saturated alcoholic solution of fuchsin, 10 cc. 



Aqueous solution of carbolic acid crystals, 5 per cent., 90 cc. 



This solution should always be carefully filtered before use. 



9. Anilin-gentian-violet. — A. Ehrlich's formula : 



Saturated alcoholic solution of gentian-violet, 1.5 cc. 



Freshly prepared anilin-water, 8.5 cc. 



The anilin-water is prepared by shaking a few drops of anilin 

 with distilled water, allowing the mixture to stand for about ten 

 minutes, and then filtering through well-moistened filter-paper. 

 The filtrate should contain no globules of the anilin. In order to 

 avoid this the filtration should be stopped before all the watery 

 part of the mixture has run through the paper, otherwise oily drops 

 of anilin will follow. 



Precipitates are likely to occur in this gentian-violet solution 

 when it is first prepared. After twenty-four hours these are less 

 abundant. The solution deteriorates soon after that time, and 

 should not be used more than a week after its preparation. 



B. Stirling's formula : 



Gentian-violet, 5 grams. 



Alcohol, 10 cc. 

 Anilin, 2 cc. 



Distilled water, 88 cc. 



This solution keeps better than the preceding. Both must be 

 filtered carefully through moistened filter-paper immediately before 

 being used. 



