252 TUBERCULOSIS. 



duced in this way is by no means small. And furthermore, 

 although the ox is little susceptible to human tubercle bacilli, 

 tuberculosis with general infection has been produced in calves- 

 by means of them on more than one occasion. Such a result 

 has been obtained by Ravenel, and also, in this country, by 

 Delepine. There are also facts which go to show that tubercle 

 bacilli cultivated from lesions in young children have a higher 

 degree of virulence for animals than those obtained from adults ; 

 that is, they resemble more the bovine tubercle bacilli; this 

 is what one might expect if the bacilli in question had come 

 comparatively recently from the tissues of the ox. As at pres- 

 ent the subject is still under investigation in this and other 

 countries, it would not be justifiable to dogmatise, but in the 

 meantime, we see no sufficient reason to depart from the view 

 entertained up to this time, that the tubercle bacilli infecting 

 mammals are of one and the same species, though differences in 

 virulence obtain, and that milk containing tubercle bacilli is 

 a highly important source of infection to the human subject. It 

 may also be added that tubercle bacilli obtained from other 

 mammals than the ox generally correspond more closely, as 

 regards their virulence or inoculation, with bovine than with 

 human bacilli. 



2. Avian Tuberculosis. — In the tubercular lesions in birds 

 there are found bacilli which correspond in their staining reac- 

 tions and in their morphological characters with those in mam- 

 mals, but differences are observed in cultures, and also on 

 experimental inoculation. These differences were first de- 

 scribed by Maffucci and by Rivolta, but special attention was 

 drawn to the subject by a paper read by Koch at the Interna- 

 tional Medical Congress in 1890. Koch stated that he had 

 failed to change the one variety of tubercle bacillus into the 

 other, though he did not conclude therefrom that they were 

 quite distinct species. The following points of difference may 

 be noted. 



On glycerin agar and on serum, the growth of tubercle bacilli from birds 

 is more luxuriant, has a moister appearance (Fig. 89, C), and, moreover, takes 

 place at a higher temperature, 43.5° C, than is the case with ordinary tubercle 

 bacilli. Experimental inoculation brings out even more distinct differences. 

 Tubercle bacilli derived from the human subject, for example, when injected 

 into birds, usually fail to produce tuberculosis, whilst those of avian origin 

 very readily do so. Birds are also very susceptible to the disease when fed 



