92 GENERAL MICROBIOLOGY 



EXERCISE 30. METHOD OF STAINING TUBERCLE 

 AND OTHER ACID-FAST BACTERIA 



Acid-fast bacteria are so termed from their reaction to 

 a special staining process. This process consists in staining 

 the specimen containing, for example, tubercle bacteria, 

 with hot carbol-f uchsin and decolorizing for a short time 

 with acid; the acid takes the dye out of all other material, 

 bacteria and blood or other body cells that may be present, 

 leaving the tubercle bacteria stained red. This staining 

 process is essentially the same as for spores, but the prin- 

 ciple is different. 



The property which some bacteria possess of being 

 acid-fast is attributed to the presence of fat and wax-like 

 substances in their cells. This seems to be proved by the 

 fact that when the bacterial cell substance of tubercle 

 bacteria has been freed from these fats and waxes by 

 extraction with absolute alcohol and ether, this property 

 is lost. 



Apparatus. Clean slides; clean cover-glasses; plati- 

 num loop; copper staining dish; Bunsen burner; forceps; 

 carbol-f uchsin; sulphuric acid, 20%; methylen blue, aque- 

 ous-alcoholic; immersion oil; Canada balsam; specimen 

 to be examined. 



Method. 1. Using a sterile loop, smear some of the 

 specimen in the center of one surface of a clean slide, 

 taking care not to come within 0.5 cm. of the edge. 



Note. This may be applied to sputum, pus, etc. In case of 

 tubercles or diseased organs or tissues these may be cut open with a 

 scalpel, a portion incised, and grasping this portion with the forceps 

 a smear made directly on the slide, following the precautions above. 

 If pure cultures are to be examined, a cover-glass specimen may be 

 made in the usual way. 



2. Dry the slide in air. 



3. Fix in the flame. 



4. Support the slide on the copper staining dish; flood 



