280 



TUBERCULOSIS 



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 diminish. The vitality of the bovine type 

 is less on artificial 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., 

 those of Del^pine, Hamilton, 

 and Young, general tubercu- 

 losis has been produced in 

 the bovine species by tubercle 

 bacilli from the human sub- 

 ject, but these results are 

 exceptional.) Corresponding 

 differences come out in the 

 case of the rabbit ; in fact, 

 intravenous injection of suit- 

 able quantities {e.g., of Ol-0'Ol mgrm. of dried bacilli sus- 

 pended 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 

 of the two types of organisms, it may be stated that, so far as 

 we know, the bacillus obtained from bovine tuberculosis is 



Fig. 80. — Cultures of bovine and human 

 bacilli 5 weeks old on glycerin egg. 

 The central tube is human, the tube 

 on each side bovine. The three tubes 

 were inoculated on the same day. 



