14 MICRO-ORGANISMS AND DISEASE [CHAP. 



mounted in Canada- balsam (dissolved in chloroform, or 

 better still in xylol) or in Dammar varnish. 



After a very extensive experience in staining film speci- 

 mens and sections, carried on for nearly eighteen years, I have 

 come to the conclusion that for all purposes of bacteriological 

 work the following stock of dyes is sufficient : (a) methyl-blue, 

 and {i) gentian-violet, both these prepared with a saturated 

 watery solution of aniline oil as described on the previous 

 page ; for staining of cover-glass film specimens use this 

 gentian-violet aniline water, and absolute alcohol in equal 

 volumes in a watch-glass, and allow the specimen to remain 

 in this mixture for a few seconds to half a minute ; afterwards 

 wash well in water, dry and mount in balsam ; (<:) carbol- 

 fusin prepared after Ziehl i ; and (d) Lofiler's methyl-blue : 

 of a 2 per cent, watery solution of methyl-blue a little is 

 mixed with equal volume of potassic hydrate i in 10,000 ; 

 the staining must be of a prolonged character ; after 

 staining, wash well in water acidulated with acetic acid. 

 (e) Alcoholic solution of eosin J per cent. ; (/) watery 

 solution of rubin 2 per cent. ; (g) watery solution of Bis- 

 marck-brown 2 per cent. 



J In order to bring out by the dye more conspicuously the 

 bacteria present in fluids or tissues various methods are used, 

 all of which are based on the principle that the bacteria have 

 an affinity to the dye which is greater than that of the tissue- 

 elements. Hence after staining, the tissue-elements may 

 be decolourised without abstracting the colour from the 

 bacteria. Cover-glass specimens or sections, after having 

 been well stained with a dye, are subjected to various 

 decolourising re-agents, whereby the tissue-elements become 

 deprived of the dye, but the bacteria retain it. Although in 



^ I '5 grammes fiichsin, 10 cc. absolute alcohol, 100 cc. of a 5 per cent, 

 watery phenol solution. 



