266 



TUBERCULOSIS 



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 comparatively small size and remain separate, be- 

 coming 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 

 surface of the serum and 

 at the bottom of the tube 

 may grow over the sur- 

 face of the condensation 

 water on to the glass 

 (Fig. 79, A). The growth 

 is always of a dull ap- 

 pearance, and has a con- 

 siderable degree of con- 

 sistence, so that it is 

 difficult to dissociate a 

 portion thoroughly in a 

 drop of water. In older 

 cultures the growth may 

 acquire a slightly brown- 

 ish or buff colour. When 

 the small colonies are 

 examined under a low 

 power of the microscope, 

 they are seen to be ex- 

 tending at the periphery 

 in the form of wavy or 

 sinuous streaks which 

 radiate outward, and 

 which have been com- 

 pared 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- 

 gresses more rapidly than on serum, but this medium is not 

 suitable for obtaining cultures from the tissues, inoculations 

 with tubercular material usually yielding a negative result. 



FIG. 79. Cultures of tubercule 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. 



