THE METHODS OF STAINING MICROBES 75 



method the tubercle-bacilli and certain other patho- 

 genic microbes are stained red, while the putrefac- 

 tive bacteria and micrococci are blue. This method 

 is a rapid one, and is, consequently, recommended 

 for the busy medical man. 



The Ziehl-Neelsen method of staining the tubercle- 

 bacilli is a modification of the Ehrlich-Weigert 

 method already described. The cover-glass prepara- 

 tions or sections are stained in the following dye : 

 1 gramme of fuchsiue is dissolved in 10 cc. of 

 absolute alcohol, and to this is added 100 cc. of an 

 aqueous solution of carbolic acid (5 per cent.). The 

 mixture is then heated. In the hot dye sections are 

 stained in six or seven minutes ; and cover-glass 

 preparations are stained in about three minutes. 

 The preparations or sections are now placed for a 

 second or so in 90 per cent, alcohol, then in dilute 

 sulphuric acid (25 per cent.), when the pink colour is 

 replaced by a yellowish brown. The preparations, 

 etc., are then transferred to a solution of lithium 

 carbonate. They are afterwards stained in an 

 aqueous solution of methylene blue, cleared in oil 

 of cloves, and mounted in Canada balsam. This 

 method (also known as the carbol-fuchsine method) 

 gives excellent results. 



To ascertain the presence of tubercle-bacilli in 

 tuberculous milk, the best plan is to pass the milk 

 through one of the ordinary centrifugal machines 

 used in the dairy ; and then to take the sediment 

 (after the separation of the cream and skim milk) 

 for examination. In lieu of a centrifugal machine, 

 the milk should be allowed to stand for about 



