240 



TUBEECULOSIS 



there appear in from ten to fourteen days minute points of 

 growth of dull whitish colour, rather irregular, and slightly raised 

 above the surface (it is advisable to plant on the medium an 

 actual piece of the tubercular tissue and to fix it in a wound of 

 the surface of the serum). Koch compared the appearance of these 

 to that of small dry scales. In such cultures the growths usually 



reach only a compara- 

 tively small size and re- 

 main separate, becoming 

 confluent only when many 

 occur close together. In 

 sub - cultures, 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 surf ace of the serum 

 and at the bottom of the 

 tube may grow over the 

 surface of the condensa- 

 tion water on to the glass 

 (Fig. 84, A). The growth 

 is always of a dull ap- 

 pearance and has a con- 

 siderable degree of con- 

 sistence, so that it is diffi- 

 cult to dissociate a portion 

 thoroughly in a drop of 

 water. In older cultures 

 the growth may acquire 

 a slightly brownish or buff 

 colour. When the small 

 colonies are examined 

 under a low power of the 

 microscope they are seen 



to be extending at the periphery in the form of wavy or sinuous 

 streaks which radiate outward and which have been compared 

 to the flourishes of a pen. The central part shows similar 

 markings closely interwoven. These streaks are composed of 

 masses of the bacilli arranged in a more or less parallel manner. 

 " On glycerin agar, which was first introduced by Nocard and 

 Roux as a medium for the culture of the tubercle bacillus, 

 growth takes place in sub-cultures at an earlier date and pro- 



A B C 



FIG. 84. Cultures of tubercle bacilli on 

 glycerin agar. 



A and B. Mammalian tubercle bacilli ; 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. 



