CULTIVATION OF TUBERCLE BACILLUS. 



231 



bacilli, though some retain the colour with equal tenacity. 

 Tubercle bacilli also stain by Gram's method, but the 

 results are inferior to those obtained with carbolic fuchsin. 



Cultivation. The medium first used by Koch was 

 inspissated blood serum (inde p. 50). If inoculations are 

 made on this medium 

 with tubercular 

 material free from 

 other organisms, 

 there appear from the 

 tenth to fourteenth 

 day minute points of 

 growth of dull whitish 

 colour, rather ir- 

 regular, and slightly 

 raised above the 

 surface. In such 

 cultures they usually 

 reach only a com- 

 paratively small size 

 and remain separate, 

 becoming confluent 

 only when many 

 occur close together. 

 Koch compared the 

 appearance of these 

 to that of small dry 

 scales. In sub-cul- 

 tures, however, 

 growth is more 

 luxuriant and may 

 come to form a dull 

 wrinkled film of whitish colour, which may cover the greater 

 part of the surface of the serum and at the bottom of the 

 tube may grow over the surface of the condensation water 

 on to the glass (Fig. 64, A). The growth is always of a dull 

 appearance and has a considerable degree of consistence, it 

 being difficult to dissociate a portion thoroughly in a drop 



B c 



Cultures of tubercle bacilli on 

 glycerine agar. 



A and B. Mammalian tubercle bacilli 



A 



FIG. 64.- 



A is an 



old culture, B one of a few weeks' growth. 

 C. Avian tubercle bacilli. The growth is whiter 

 and smoother on the surface than the others. 



