4° METHODS OF EXAMINATION. 



placed in the following solution for from twelve to twenty-four 

 hours : — 



Methyl blue concentrated alcoholic solution, . i part. 



Distilled water, . . . .200 parts. 



10 per cent, caustic potash solution, . . 2 parts. 



Stir this mixture well and frequently. 



Then immerse the cover-glass for a couple of minutes in a watery 

 solution of vesuvin, until the blue coloration has disappeared, rinse 

 with distilled water, examine at once, or allow the film to dry 

 thoroughly, and then mount in Canada balsam. Sections may be 

 cleared up with clove oil or cedar oil, as recommended by Koch. 



By this method the tubercle bacilli are stained blue, and the rest 

 of the tissues, pus corpuscles, &c. brown. Ehrlich sought to sim- 

 plify the process, or rather to render the detection of the bacilli more 

 certain, by using one of the mineral acids as a decoloriser, having 

 found by experiment that the acid had no effect upon the rods stained 

 with gentian violet or fuchsin, although other tissues were rendered 

 colourless. Koch very early adopted Ehrlich's plan, which is as 

 follows, as given by Koch. ^ 



Stain sections of tissues or films on cover-glasses for at least 

 twelve hours in the following solution : — 



Saturated alcoholic solution of methyl violet or fuchsin, 1 1 parts. 



Aniline water, . . . . .100 parts. 



Absolute alcohol, . . . . .10 part's. 



The staining of films on cover-glasses may be accelerated by 

 gently heating the staining solution until steam rises from the 

 surface. Such preparations are stained in from a quarter to half 

 an hour under these conditions. Pass the preparations rapidly 

 through a dilute (one to three) watery solution of nitric acid, care 

 being taken that this is perfectly free from nitrous acid, that sections 

 are never allowed to remain more than a few minutes — two or 

 three — and cover-glasses half a minute. Any colour that remains 

 after this is perfectly soluble in sixty per cent, alcohol, but it 

 is by no means so soluble in water, hence the preparations are 



1 R. Koch, " Die ^tiologie der Tuberkulose : "' Maltheil. aus dent Kaiserl. 

 Gesundheitsatnte, vol. ii. ' 



