THE MICROSCOPE AND MICROSCOPIC METHODS 47 



Bacillus of bubonic plague, 

 Bacillus of glanders (Bacillus mallei), 

 Bacillus proteus, 

 Spirillum of Asiatic cholera, 

 Spirillum of relapsing fever. 

 Staining of Acid-proof Bacteria. — A very large number of 

 methods have been proposed for staining the tubercle bacillus, 

 all of which depend upon the principle that, after adding to 

 solutions of aniline dyes certain substances, like aniline water, 

 carbolic acid, or solutions of ammonia or soda, the tubercle bacillus 

 is stained with great intensity, and gives up its stain with difficulty. 

 Solutions of acids will remove the stain from all parts of the prepa- 

 ration excepting from the tubercle bacilli, which retain the dye, 

 having once acquired it. The rest of the preparation may now 

 be given a different color — contrast-stain. 



Bacilli that resist decolorization by acids are called acid-proof 

 or acid-fast. 



Some acid-proof bacteria : 

 Bact. tuberculosis, 

 Bact. leprae, 

 Bact. smegmatis. 

 Grass bacillus of Moeller, 

 Butter bacillus of Rabinowitsch, 

 Certain strep tothrices, 



Certain baciUi common in the feces of cattle, 

 Certain bacteria found in distilled water, 

 Spores of many bacteria. 

 Occasionally other bacteria, micrococci and horny epithelial 

 cells are imperfectly decolorized, but their forms distinguish 

 them from tubercle bacilli. Minute crystalline needles which 

 have a shape like that of bacilli, are often encountered in sputum, 

 but"their nature will be recognized after a little practice. 



The stain for acid-proof bacteria is most frequently used for 

 specimens of 'sputum from cases of suspected pulmonary tubercu- 

 losis; it may be applied to other fluids and secretions equally 



