TUBERCLE BACILLUS 6l 



Culture. The organism is aerobic and facultatively 

 anaerobic. On ordinary media growth is either absent 

 or scanty. It grows best at blood-heat, growth being 

 extremely slow; no appreciable evidence being shown 

 under four to six weeks. Primary cultures are made on 

 Dorset's egg medium, glycerin agar cum egg-yolk, or 

 glycerinated potato. In glycerin broth it develops as 

 a floating pellicle. On glycerin agar it gives a cream or 

 brownish-yellow film which is dry and wrinkled. A pure 

 culture can be obtained by the inoculation of tubercular 

 sputum into a guinea-pig. After three to six weeks the 

 animal is killed, and matter from the tubercles is streaked 

 over glycerin potato (a semicylinder of potato in a Roux's 

 potato tube, the bulb being filled with 5 per cent, glycerin). 

 In six or eight weeks a fair number of the tubes will show 

 a growth. The organism does not liquefy gelatin. On 

 repeated subculture it becomes longer and thicker; clubbed 

 and branching forms may develop, which leads some to 

 class the bacillus with the trichomycetes. As a sapro- 

 phytic habit is developed the virulence is diminished, 

 but can be restored by passage through an animal. 



Staining Reactions. Ordinary stains have little effect 

 on the organism, but it stains well by Gram's method 

 and the Ziehl-Neelsen method. Much concluded that 

 three forms of the organism exist: (1) The ordinary 

 'acid-fast' bacillus; (2) a bacillus that is not acid-fast; 

 and (3) free granules also not acid-fast. Whether these 

 last two forms are degenerate organisms or resistant 

 types remains unproved. At any rate it appears un- 

 questioned that the non-acid-fast granules on injection 

 into animals produce tuberculosis due to the ordinary 

 acid-fast bacillus. 



In addition to being acid-fast, the tubercle bacillus is 

 also " alcohol-fast," a property that serves to distinguish 

 it from the smegma and similar bacilli which lose their 

 stain in alcohol treatment. Inasmuch as smegma bacilli 

 may occur in urine, sputum, and other material frequently 

 examined for tubercle, it is advisable to apply alcohol 

 to fuchsin- stained preparations as a routine process, 

 especially as it can be combined with acid treatment. 

 Instead of using 25 per cent, sulphuric acid the fuchsin 

 preparation is decolorised in acid alcohol (3 per cent, 

 hydrochloric acid in alcohol) till almost white. 



