272 TUBERCULOSIS 



medium the organism grows well, producing an abundant 

 wrinkled layer which has usually a yellowish, buff, or pinkish 

 colour. These media are specially suitable for direct cultivation 

 from the tissues. 



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. 

 The growth has practically the same characters as on serum. 

 The organism also flourishes well on glycerin potato, and this 

 medium is suitable for primary cultures from tubercular lesions. 

 In glycerin broth, 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 superficially 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. The use of animal 

 tissues in glycerin bouillon as a medium for the growth of the 

 tubercle bacillus' has been introduced by Frugoni, and is one 

 which gives excellent results. He recommends that small 

 wedges of rabbit's lung should be sterilised in the autoclave, and 

 placed in tubes of glycerin bouillon in such a way that their 

 surface is kept moist by the medium, without the fragments 

 being submerged. The growth is probably more rapid and 

 luxuriant than in any other method. 



The optimum temperature for growth is 37° to 38° C. 

 Growth ceases about 42° and usually below 28°, but on long- 

 continued cultivation outside the body and in special circum- 

 stances growth may take place at a lower temperature, e.g., 

 Sander found that growth took place in glycerin-potato broth 

 even at 22° to 23° C. 



Powers of Resistance. — Tubercle bacilli have considerable 

 powers of resistance to external influences, and can retain their 

 vitality for a long time outside the body in various conditions ; 

 in fact, in this respect they may be said to occupy an inter- 

 mediate position between spores and spore-free bacilli. Dried 

 phthisical sputum has been found to contain still virulent 

 bacilli after two months, and similar results are obtained 

 when the bacilli are kept in distilled water for several weeks. 



