TUBERCULOSIS 123 



is about the same whether oxygen is supplied or withheld, 

 but is prejudicially affected by light, diffused daylight 

 being fatal to a culture in four or five days, while direct 

 sunlight is fatal in a few hours, the time necessary to kill 

 the bacilli varying according to the thickness of the culture. 



Growth on Media. — Koch first succeeded in cultivating the 

 bacillus on solidified blood serum, on which it grows very 

 slowly. In 1888 Nocard and Eoux showed that excellent 

 growths are obtainable on agar containing 8 per cent, of 

 glycerine in half the time required to produce a similar 

 characteristic growth on blood serum. Typical growths 

 appear on blood serum in three to four weeks, while four- 

 teen days suffice for a culture on glycerine agar. The 

 growth on either medium appears as a peculiar whitish 

 wrinkled skin on the surface, somewhat resembling the 

 ' casts ' formed by earthworms in soft mould. 



It is stated by Wurtz that broth to which a slight 

 addition of glycerine has been made serves well for the 

 growth of the tubercle bacillus, which develops as a float- 

 ing skin on the surface. 



In the lungs invaded by tubercle the bacillus is found in 

 greatest numbers round the circumference of the ' giant- 

 cells.' Matter derived from the middle of these will never- 

 theless produce tuberculosis on inoculation into a guinea- 

 pig, the explanation given being that the bacilli in the centre 

 of the cell have disappeared, leaving spores behind them. 



Spores are formed by the bacillus whenever it finds itself 

 under conditions unfavourable to its growth, such as want 

 of nourishment, moisture, or a suitable temperature. 



A pure culture is readily obtained by inoculation of a 

 guinea-pig with tuberculous sputum ; after two or three 

 weeks the animal is killed, and its lungs opened with anti- 

 septic precautions : a streak is made from an affected part 

 (in which the bacillus exists as a pure culture) on to media. 



