208 BACTERIOLOGY 



glasses infected with the crushed tubercular masses are 

 now laid upon serum which has been poured out into glass 

 capsules and inspissated, the tubercular mass is smeared 

 over the surface of the serum with a strong platinum wire, 

 and the capsules are covered with glass plates and placed in 

 the incubator. The colonies are perfectly formed in about 

 three weeks, when further cultures can be made from them 

 in test-tubes. When examined under a low power, the 

 cultures show figures coiled in the shape of an S and 

 thickened in the centre, which consist of bacilli massed 

 together (fig. 81). The colonies form dry, white scales, 

 having a dull surface and not larger than poppy- seeds, which 

 adhere but loosely to the surface of the medium, never 

 penetrate into its substance, and do 

 not liquefy it (fig. 82). 



Pastor gives the following pro- 

 cess for obtaining pure cultures of 

 tubercle bacilli from sputum : A 

 patient is chosen whose sputum is 



FIG. 81. IMPRESSION PREPARA- 

 TION FROM A CULTURE OF TU- very rich in bacilli and shows coin- 



EERCLE BACILLUS ON SERUM. 



paratively little contamination with 



other micro-organisms, and he is made to rinse out his 

 mouth and pharyngeal cavity repeatedly with distilled water, 

 and then to expectorate into a sterilised test-glass. The 

 sputum, or more properly the liquid contents of the pul- 

 monary cavities, is shaken up with sterilised water and 

 filtered through fine gauze to remove the coarser particles. 

 A few drops of the filtrate are mixed with melted nutrient 

 gelatine in such a manner as not to render it very 

 turbid, and the mixture is poured out on plates which are 

 left under bell-glasses at room temperature. In from three 

 to four days the various colonies of bacteria contaminating 

 the sputum form. The portions of gelatine between the 

 colonies, and which still remain clear, are now sought out 



