6i4 



LABORATORY HINTS 



Important Differentiations. 



Most organisms when stained with fuchsin are readily decolorized 

 by weak solutions of mineral acids. The exceptions are : Tubercle 

 bacillus, bacillus leprcC, smegma bacillus, the bacillus of timothy 

 grass, the dung bacillus and others less important. 



If an organism retains its stain after treatment by 25 per cent. 

 H2SO4 or 30 per cent, nitric it is acid-fast. 



The Acid-Fast Method. 



Stain with warm carbol fuchsin, five minutes. (To warm, heat a 

 penny over a Bunsen flame and place slide upon it. Repeat the 

 process during five minutes.) 



Decolorize with 20 per cent, strong HoSO,, HXO3 or HCl. 



Wash well, dry and mount if a film; dehydrate, clear and mount if 

 a section. 



Some organisms are so rapidly decolorized that they are not seen, 

 as the pneumo-bacillus. For these use aniline oil instead of acid 

 alcohol. 



Weigert's Method. 



Aniline gentian violet, five minutes. 

 Gram's iodine, two minutes. 



Pour off, treat with aniline oil, then stop its action with water. 

 Counterstain other Grams with Bismarck brown one minute, or 

 aqueous eosin 20 seconds. 

 Wash, dry and mount. 



