VARIETIES OF TUBERCULOSIS 275 



in the case of the rabbit; in fact, intravenous injection of 

 suitable quantities 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 sub- 

 cutaneous 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 tyiws of organisms, it may be stated that, so far as we 

 know, the bacillus obtained from bovine tuberculosis is always 

 of the bovine type, and the same may be said to be true of 

 tuberculosis in pigs ; in fact this seems to be the prevalent 

 <>ri:aiii>!it in animal tuberculosis. In human tuberculosis the 

 bacilli in a large majority of the cases are of the human type ; 

 but, on the other hand, in a certain proportion bacilli of the 

 bovine type are present, the bacilli when cultivated being 

 indistinguishable by any means at our disposal from those 

 obtained from bovine tuberculosis. The Royal Commission 

 found the bovine type in 14 out of 60 cases of human 

 tuberculosis a somewhat higher proportion than has been 

 obtained by most other investigators and in all of these, 

 with one exception, the bacilli were obtained either from caseous 

 cervical glands, or from the lesions of primary abdominal tuber- 

 culosis, that is from cases where there was evidence of infection 

 by alimentation. It is also to be noted that almost all the 

 tubercular lesions from which the bovine type has been obtained 

 have btrn in children. The general result accordingly is that 

 bovine tubercle bacilli are present in a certain proportion of 

 caaea of tuberculosis in young subjects, and that these are 

 r-pccially cases where infection by the alimentary canal has 

 occurred. It must thus be held as established that tuberculosis 

 is transmissible from the ox to man, and that the milk of 

 tubercular cows is a common vehicle of transmission. 



Although most of the bacilli which have been cultivated 

 correspond to one of the two types, as above described, it is 

 also to % be noted that intermediate varieties are met with. It 

 has also been found that the type characters of the bacillus are 

 not constant. Various observers have found it possible to 

 modify bacilli of the human type by passing them through the 

 bodies of certain animals, e.y. guinea-pigs, sheep, and goats, So 

 that they acquire the characters of bovine bacilli. In view 

 of these facts, it is probable that bovine bacilli will undergo 

 corresponding modifications in the tissues of the human subject 

 what period of time is necessary for such a change we 



