ACID-FAST GROUP 313 



Equal quantities of the two solutions are mixed for use. The 

 sputum or other material containing the tubercle bacilli is placed 

 in a centrifuge tube, and antiformin to about 20 per cent, of its 

 bulk, added. The tube is then corked, thoroughly shaken, and al- 

 lowed to remain in a dark place for twenty-four hours. It is then 

 centrifuged, the clear, supernatant liquid pipetted off, the tube 

 filled with sterile physiological salt solution, centrifuged, washed 

 a second time, and the sediment smeared over the surface of serum 

 slants. The antiformin destroys all other non-acid-fast bacteria 

 present and dissolves the mucus and most of the cell elements, 

 but when properly used, seems to have little effect upon the tuber- 

 cle bacilli, as they retain their vitality unimpaired. This is prob- 

 ably because of their chemical composition and waxy covering. 



Cultural Characters. B. tuberculosis does not grow readily 

 when first isolated upon culture-media, and will grow only upon 

 certain substances. After a few transfers it seems to become ha- 

 bituated to growth under these conditions and will develop through 

 a much greater range of temperature and on other media. Devel- 

 opment occurs best on media containing blood-serum, egg, or 

 similar proteins, or to which glycerin has been added. 



The colonies upon blood-serum or glycerin agar appear in the 

 course of ten days or two weeks as tiny grains barely visible to the 

 naked eye. They gradually enlarge, and in subcultures become 

 confluent and cover the surface of the medium with a dry, rather 

 mealy, wrinkled growth; the colonies direct from lesions do not 

 coalesce usually. The growth is white and lusterless, or rarely in 

 old cultures cream or brown. In glycerin bouillon the growth 

 generally occurs as a more or less continuous, heavy, wrinkled, 

 white pellicle that breaks into pieces and sinks to the bottom when 

 the medium is shaken. Similar growths occur upon other media 

 which contain glycerin. In no other case is the growth so rapid. 



Cultural characters which may be used in the certain differen- 

 tiation of the human, bovine, and avian tubercle bacilli are not 

 readily found. The organisms isolated from the human and from 

 the bird adapt themselves much more readily to artificial media 

 and grow more luxuriantly than does the bovine type. 



Physiology. The B. tuberculosis is aerobic. Its optimum 

 growth temperature is about 37.5 for the human and the bovine 



