A NEW CULTURE MEDIUM FOR THE TUBERCLE 



BACILLUS 



WM. WHITRIDGE WILLIAMS and WARD BURDICK 



(From the Laboratory of the National Jewish Hospital for Consumptives, Denver, 



Colorado 



Contamination is an occurrence which has always troubled 

 bacteriologists in the isolation and cultivation of the tubercle 

 bacillus. Even the various digestive methods which are used 

 at present, such as the antiformin, the sodium carbonate, and 

 the sodium hydroxid methods, have failed to yield uniformly sat- 

 isfactory results. It is obvious that the ideal culture medium 

 for this purpose would be one which included some substance 

 that had the property of preventing the growth of other micro- 

 organisms while not interfering with the isolation and repro- 

 duction of the tubercle bacillus. 



The observation of v. Drigalski and Conradi (1902), that 

 crystal violet was able to inhibit the growth of many bacteria 

 but had no effect on the cultivation of typhoid and colon baciUi 

 was the first step in this direction. Then followed the splendid 

 researches of Churchman (1912) who worked with a number 

 of common dyes and discovered that gentian violet possessed 

 a striking selective power. He found that by making divided 

 plates, one-half filled with plain agar and the other filled with 

 agar to which 0.001 per cent gentian violet was added, and 

 stroking the surface with a mixed culture, he could get rid of 

 the contaminating organisms. For instance, by this means he 

 purified a culture of B. tuberculosis which had become contami- 

 nated with B. suUilis. The former organism is ''gentian-nega- 

 tive" while the latter, like almost all air contaminations, is 

 ''gentian-positive." He states that the effect of gentian violet 

 on gentian-positive organisms is better described as bacteriostatic, 

 rather than bactericidal, meaning that the dye suspends repro- 



411 



