STAINING TUBERCLE BACTERIA 6"] 



EXERCISE XX 



STAINING TUBERCLE BACTERIA (BACILLI) 



98. The stained tubercle bacteria possess, because of the 

 layer of fatty acids covering them, the power of retaining 

 the coloring matter even when treated with a strong decolor- 

 izer, such as a solution of sulphuric or nitric acid. On this 

 account staining has a high differential value which is made 

 use of in identifying this organism. Thus in the examination 

 of sputum in cases of suspected tuberculosis the object is to 

 determine the presence of tubercle bacteria. As this organism 

 is not easily cultivated, the staining process is very largely 

 depended upon in making a differential diagnosis. 



99. Work for this exercise. Make 4 cover-glass prepara- 

 tions from a culture of tubercle (furnished). Stain 2 of them 

 with tubercle stain and carefully describe the appearance of 

 the bacteria and illustrate with a few drawings. 



Stain 2 of the preparations after Gabbett's method. 



Stain a cover-glass preparation of tubercular sputum (fur- 

 nished). 



For the next exercise liquefy two large tubes of agar and two 

 of gelatin and pour them into Petri dishes. After the medium 

 has solidified remove the covers of the Petri dishes and expose 

 one of each to the air for five minutes and one of each for 

 ten minutes. Return the covers and place the agar plates in 

 the incubator and the gelatin ones in the locker. When these 

 plates are examined in the next and subsequent exercises there 

 will be a colony for each bacterium that fell upon the medium 

 from the air. It will be necessary to look out for impure or 

 mixed colonies, as two or more organisms may have fallen 

 together. 



Read the directions in the text-books for staining tubercle 

 bacteria (bacilli). 



