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oil in water, 1 made by adding the oil, drop by drop, to 

 distilled water in a test-tube, which is meanwhile con- 

 stantly shaken ; upon saturation, indicated by turbidity, 

 the mixture is filtered. To the clear filtrate are added a 

 few drops of (b) a saturated alcoholic solution of an ani- 

 line pigment, preferably fuchsin. Upon the appearance 

 of turbidity (or opalescence) the staining fluid is ready for 

 use (though it is by some observers thought desirable to 

 filter before using). In this liquid sections of tissue or 

 layers of sputum on cover-glasses (prepared as already 

 directed)lie twenty -four hours at ordinary temperatures, 

 or thirty to sixty minutes if the temperature be main- 

 tained at 50 C. At the end of this time all the ele- 

 ments, bacilli included, are stained ; in order to differen- 

 tiate the bacteria the section (or cover-glass) is immersed 

 for a few seconds in a mixture of nitric acid (one part) 

 and water (three parts). The color disappears at once, 

 and after washing the section in water and mounting in 

 the usual way, it will be found that the bacilli only ex- 

 hibit a deep color, the other objects in the field having 

 little or no color. The staining is now complete the 

 red bacilli appearing against a white background ; yet a 

 pleasing contrast may be obtained by coloring this back- 

 ground blue ', this is easily accomplished by immersing 

 the decolorized section or cover-glass in the ordinary 

 two per cent, watery solution of methylene blue. The 

 already stained tubercle bacilli (red) are unaffected by 

 the second dye and retain the first color ; while nuclei, 

 etc., absorb the second (blue) color only. 



The aniline oil should be fresh, for in time it becomes 

 oxidized, a condition indicated by a dark instead of the 

 original light brown hue ; in this condition the result of 

 staining is uncertain. The bacilli are in some cases 

 simulated in size and shape by minute crystals, but are, 

 however, easily distinguished from the latter by the bril- 

 liant red color which the true bacilli exhibit (when stained 



1 Those who cannot conveniently procure the oil will find an excellent substitute 

 in ordinary (pure) carbolic acid. The directions for use remain as above with the 

 substitution of the words " carbolic acid " for " aniline oil." 



