RELATIONS OF MAMMALIAN AND AVIAN TUBERCULOSIS. 573 



Tuberculosis of the Psittaceae, unlike that of the Gallinacege, is 

 therefore much more virulent for the guinea-pig than for the rabbit. 

 In this respect it more closely resembles tuberculosis of mammals, 

 with which it also agrees in being comparatively harmless for the 

 Gallinacese (Experiments 5 and 7). 



Bearing in mind the results already obtained, we have now to con- 

 sider the relations existing between the tuberculosis of mammals and 

 that of birds. 



Avian tuberculosis, which is ver}^ frequent in the Gallinaceae, can be 

 transmitted to the fowl, pigeon, and the rabbit, and, with less facility, 

 to the guinea-pig. It may also occur, with its own special characters, 

 in the ox and in man (Kruse's and Pansini's cases). 



Mammalian tuberculosis affects man, the dog, ox, and horse, and 

 is readil}- conveyed to the guinea-pig and rabbit, which, however, is 

 perhaps less sensitive to it than to avian tuberculosis : it can also be 

 inoculated into the parrot, and sometimes the fowl. 



The two viruses, therefore, affect the same animals. The titles 

 given them are, therefore, not precisely correct, for the so-called tuber- 

 culosis of mammals is identical with that very commonly seen in 

 parrots. 



These results, therefore, render the barrier which was erected 

 between the two viruses very narrow. Though it is allowable and 

 necessar}' to admit the existence of two races of tubercle bacilli, it 

 seems to us exaggeration to speak of two species. Between the 

 extreme t\pes numerous transition forms exist, and one variety can 

 sometimes be transformed into the other. We have shown, for 

 example, that the avian virus, after several passages through mam- 

 mals, may lose its virulence for the Gallinaceas ; and conversely that 

 human tuberculosis, when by chance conveyed to a fowl, may sometimes 

 be afterwards passed through a series of fowls. But to obtain such 

 positive results it is necessary to multiply experiments, and not to 

 rest content with a few. For this reason we inoculated eighty-six 

 fowls with human, and fort}-two guinea-pigs with avian virus. It will 

 be conceded that so large a number of experiments gives a certain 

 weight to our conclusions. 



To sum up, we have no intention of attempting to establish a 

 complete parallel between the tuberculosis of Gallinaceae and that of 

 mammals. They show notable differences which we were not the last 

 to recognise, but we continue to believe that, however important their 

 distincti\-e characteristic? ma}' be, the\' are insufficient to destroy the 

 unicist theor\- of tuberculosis. 



