TUBERCLE BACILLI IN SECTIONS OF TISSUE 217 



however, of an apparatus for this purpose, Des Vos mixes 

 white of egg with four times its bulk of distilled water, which 

 causes the globulines to sink to the bottom as a coarsely 

 flocculent mass. Up to 10 c.cm. of the supernatant opales- 

 cent liquor, which consists of dilute albumen, are now added 

 to the fluid to be examined, and the whole is well shaken 

 up and heated in the water-bath until the white of egg 

 coagulates. In a short time, according to the quantity of 

 white of egg added, a greater or less amount of a finely 

 flocculent sediment forms, which is to be examined for 

 bacilli. 



To examine milk for tubercle bacilli, the most con- 

 venient mode is to place a drop of the suspected milk upon 

 a cover-glass and add to it two or three drops of a 1 per 

 cent, solution of sodium carbonate. The whole is well 

 mixed with a platinum needle, and the cover-glass is then 

 warmed carefully over a small flame until complete evapo- 

 ration has taken place. The fat is in this way saponified, 

 so that finally a thin film of soap remains behind on the 

 glass, which is stained, &c., like an ordinary cover-glass 

 preparation. 



Eegarding the staining of tubercle bacilli in sections of 

 tissue, the same methods hold good with suitable modifica- 

 tion, for a more detailed description of which the reader 

 may refer to the general section (see p. 84 et seq.) . Here it 

 is only necessary to remark that the usual method of stain- 

 ing employed is that with Ziehl's solution, but the sections 

 must be left lying in it for an hour or even longer. Bleach- 

 ing is carried out in 10 per cent, nitric acid for a half to 

 one minute until the red colour has vanished, after which 

 the sections are transferred to 70 per cent, alcohol until 

 they acquire a rose-red tint or become completely colourless. 

 They are then double-stained in methyl blue, thoroughly 

 "washed in alcohol, and put up in Canada balsam. The 



