242 



TUBERCULOSIS. 



glass (Fig. 89, 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 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 mark- 

 ings 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 progresses 

 more rapidly than on serum, 

 but, strangely enough, this me- 

 dium is not suitable for obtaining 

 cultures from the tissues, inocu- 

 lations with tubercular material usually yielding a negative re- 

 sult. The growth has practically the same characters as on 

 serum, but is more luxuriant. The organism, however, tends 

 to lose its virulence more rapidly than when grown on serum. 

 In glycerin brotli, especially when the layer is not deep, tubercle 

 bacilli grow readily in the form of little white masses which 

 fall to the bottom and form a powdery layer. If, however, the 

 growth be started on the surface it spreads superficiall)^ as a 

 dull whitish, wrinkled pellicle which may reach the walls of the 

 flask ; this mode of growth is specially suitable for the produc- 

 tion of tuberculin {vide infra). The culture has a peculiar 

 fruity and not unpleasant odour. On ordinary agar and on 

 gelatin media no growth takes place. 



FIG. i 



B C 



-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. 



