216 



BACTERIA 



darker. This medium is never liquefied 

 by the culture. On glycerine agar 

 made of veal broth containing 6 per- 

 cent of glycerine, the organism grows 

 well after isolation from the tissues, 

 often luxuriantly (Fig. 65). A wrinkled 

 film covers the surface of the agar, 

 from which it is removed with ease. 

 On bouillon, made of veal and glycer- 

 inized, it develops rapidly, covering 

 the medium with a dense white 

 wrinkled pellicle, which, though thick, 

 is friable. After a time it falls to the 

 bottom of the flask. It grows well on 

 glycerinized potato also, and milk 

 agar. On egg-albumins mixed together, 

 sterilized and coagulated, this bacillus 

 also develops well. 



Pathogenesis. The discovery of the 

 tubercle bacillus, its methods of culti- 

 vation and differential staining, may 

 be ranked with the greatest of medical 

 discoveries. This organism causes in 

 man and cattle, chiefly, the disease 

 called tuberculosis. It rarely attacks 

 the carnivora, but has been found in 

 such animals when confined. Swine 

 are often infected; cats and dogs some- 

 times, but sheep, goats, and horses 

 seldom. It is easy to inoculate guinea 

 pigs or rabbits by injection or feeding. 



FIG. 65. Bacillus tuberculosis; glycerine 

 agar-agar culture, several months old. 

 (Curtis.) 



