BACILLUS TUBERCULOSIS 37 



it is for primary cultures, sub-cultures grow freely, 

 forming a dry, wrinkled, or rather folded film (Fig. 31) 

 of a slightly yellowish or, when old, pinkish tinge, 

 and possessing a faint, sweet, mawkish smell. The 

 growth may thicken (Fig. 32) and form roundish 

 irregular corrugated heaps, and as in Fig. 33, this 

 mode of growth may be so marked as to produce 

 projecting, wrinkled, and folded " coral-island " like 

 masses of considerable size, as may be seen in the 

 photograph which represents the culture without 

 magnification. 



If the tube contains fluid, as it usually does, the 

 growth tends to spread over the surface forming 

 a film. This film growth is characteristic of the 

 culture in fluid media, and the extent of the growth 

 in solid media is largely dependent on the culture 

 material remaining moist. 



When freshly isolated the bacillus grows only 

 within a narrow range of temperature ; from 29 C. 

 to 42 C. Its optimum temperature is about 37 C. 

 After culture in artificial media for some genera- 

 tions the growth appears at an earlier date, and 

 the culture is freer and more rapid than when first 

 isolated, while the range of temperature within 

 which growth occurs appears to extend. 



When the glycerin e-sugar-agar medium was first 



