348 THE BACILLUS OF TUBERCULOSIS 



Precaution. The procedure of staining tubercle bacilli and finding 

 them subsequently, if they are present, is very easy, provided it is 

 done carefully and a few precautions are observed. In the first place 

 it is well to pour the suspected sputum or pus into a flat vessel, for 

 instance a Petri dish, and to place it on a dark background. This 

 makes it possible more easily to pick out with the platinum loop the 

 small flocculent tubercular masses often found in tubercular material. 

 In heating the carbol-fuchsin solution to boiling it must not be allowed 

 to evaporate down too much, because then precipitates may be formed 

 on the cover-glass. After having poured the hot stain off the cover- 

 glass, washing in water is necessary, because if it is dipped directly 

 into the dilute nitric acid the latter and the carbolic acid of the stain 

 may form a smeary substance on its surface. The cover-glass must 

 never be allowed to remain in the 10 per cent, nitric-acid solution 

 long; it should just receive a dip. If after prolonged washing in 

 alcohol, however, a good deal of red remains in the cover-glass 

 preparation a second dip in the dilute nitric acid solution is not only 

 permissible, but indicated. The watery methylene-blue solution 

 should not be too concentrated, nor should it act too long, because if 

 it does and there is much cellular material in the preparation an 

 intense blue stain may cover up a small number of red-stained tubercle 

 bacilli. When staining for tubercle bacilli in perfectly fluid media, 

 such as, for instance, urine, the fluid is first centrifuged, the super- 

 natant clear liquid decanted off, and the cover-glass preparation made 

 from the sediment, which is then treated, stained, decolorized, etc., 

 in the usual manner. 



Biedert's Sedimentation Method. When tubercle bacilli have not 

 been found in suspected sputum or tenacious caseous material the 

 material may be liquefied in order to centrifuge it and to increase the 

 chances of finding the bacilli if only a few are present. The method 

 then best used is Biedert's sedimentation method; its steps are as 

 follows : 



1. Place about a tablespoonful of the suspected material in a 

 porcelain evaporating dish and add twice the amount of distilled 

 water. Mix well by prolonged stirring with a glass rod. 

 , 2. Place the evaporating dish over a small flame and heat to 

 boiling; continue stirring constantly, and while doing so add gradually 

 ten drops of a 10 per cent, watery solution of caustic potash. Continue 

 stirring and boiling until the mixture has become entirely fluid and 

 has lost its tenacious, stringy character. 



3. Cool and centrifuge; pipette off the supernatant fluid and 

 preserve the sediment. 



4. Take some of the original untreated material and spread on 

 a cover-glass; then add some of the sediment and rub it up well with 

 the material on the cover-glass. 



5. Air dry, fix and stain, decolorize, etc., as usual. 



This method often makes it possible to find few tubercle bacilli 



