STAINING OF BACTERIA IN TISSUES. I57 



solution of potassium bichromate for five minutes. 

 This renders the gelatin insoluble, and prevents the 

 sections from leaving the slides during their necessarily 

 more or less prolonged immersion in the fuchsin stain. 

 The potassium bichromate is washed out with water, 

 and the slides are then placed in a fuchsin stain, which 

 is prepared as follows : 



Fuchsin 1.5 grammes. 



Absolute alcohol .... . . 14 c.c. 



Carbolic acid crystals, pure ... .6 grammes. 



Water . 100 c.c. 



Dissolve the fuchsin in the alcohol and the carbolic 

 acid in the water. Mix the two solutions and let stand 

 for twelve hours, with occasional shaking or stirring, 

 then filter. 



The slides are left in this solution a sufficient length 

 of time. In tissues properly hardened in alcohol the 

 tubercle bacilli stain very quickly, generally five min- 

 utes being sufficient to stain them deeply. 



Prolonged immersion in the fuchsin does no harm 

 and insures certainty of results. After a section has 

 been in the stain a sufficient length of time it, with the 

 slide to which it is cemented, is washed in water until 

 the surplus stain is removed ; it is then subjected to 

 the action of a combined decolorizer and contrast stain 

 made as follows : 



Metbyl-blue . 2.25 gramme.s. 



Absolute alcohol . . 30 c.c. 



Sulphuric acid . . . . . 12 " 



Water (distilled) . . . ... 100 " 



Dissolve the methyl-blue in the alcohol, add the acid 

 to the water, mix the two solutions, and let stand, with 

 occasional shaking, for twelve hours, then filter. 



This solution is allowed to act upon the tissue for a 



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