286 



TUBERCULOSIS 



appearance, and the growth is much more easily broken up. 

 The difference between the two types is accentuated by 

 the addition of glycerin to the medium ; this greatly favours 

 the growth of the human type, while it does not favour, or even 

 inhibits, the growth of the bovine type. In fact, on glycerin- 

 egg medium primary cultures of the latter often fail. These 

 differences are most marked in the early cultures ; in later sub- 

 cultures they tend to dimin- 

 ish. The vitality of the 

 bovine type is less on arti- 

 ficial media, cultures having 

 sometimes a tendency to die 

 out. As already stated, there 

 is also a great difference in 

 virulence towards the lower 

 animals, the bacillus from 

 the ox having a much higher 

 virulence. This organism 

 when injected in suitable 

 quantities into the ox pro- 

 duces a local tubercular 

 lesion, which is usually fol- 

 lowed by a generalised and 

 fatal tuberculosis ; whereas 

 injection of human tubercle 

 bacilli produces no more 

 than a local lesion, which 

 undergoes retrogression. (In 

 certain experiments, e.g., 



FT ?' 8 .5-- Cultu res of "bovine and human those of Delepine, Hamilton, 

 bacilli 5 weeks old on glycerin egg. j ^ T . , 



The central tube is human, the tube an ^ Young, general tubercu- 



on each side bovine. The three tubes losis has been produced in 



were inoculated on the same day. the bovine gpecieg by tuberc l e 



bacilli from the human sub- 

 ject, but these results are exceptional.) Corresponding differ- 

 ences come out in the case of the rabbit ; in fact, intravenous 

 injection of suitable quantities (e.g., of 'l-'Ol mgrm. of dried 

 bacilli suspended in 1 c.c. of saline) in this animal is the readiest 

 method of distinguishing the two types an acute tuberculosis 

 resulting with the bovine, but not with the human type. In 

 guinea-pigs and monkeys a generalised tuberculosis may result 

 from subcutaneous injection of bacilli of the human type, but in 

 this case also the difference in favour of the greater virulence of 

 the bovine type is made out. With regard to the distribution 



