AVIAN TUBERCULOSIS. 253 



with portions of the organs of birds containing tubercle bacilli, but they can 

 ■consume enormous quantities of phthisical sputum without becoming tuber- 

 cular (Straus, Wurtz, Nocard). No doubt, on the other hand, there are cases 

 ■on record in which the source of infection of a poultry yard has apparently 

 been the sputum of phthisical patients. Again, tubercle bacilli cultivated from 

 birds have not the same effect on inoculation of mammals, as ordinary tubercle 

 bacilli. When guinea-pigs are inoculated subcutaneously they usually resist 

 infection, though occasionally a fatal result follows. In the latter case, usually 

 no tubercles visible to the naked eye are found, but numerous bacilli may be 

 present in internal organs, especially in the spleen, which is much swollen. 

 Further, intravenous injection even of large quantities of avian tubercle bacilli, 

 in the case of dogs, leads to no effect, whereas ordinary tubercle bacilli pro- 

 'duce acute tuberculosis. [The rabbit, on the other hand, is comparatively 

 •susceptible to avian tuberculosis (Nocard) .] 



There is, therefore, abundant evidence that the bacilli derived ' 

 from the two classes of animals show important differences, and, 

 reasoning from analogy, we might infer that probably the human 

 -subject also would be little susceptible to infection from avian 

 tuberculosis. The question remains, are these differences of a 

 permanent character .■■ The matter seems permanently settled 

 -by the experiments of Nocard, in which mammalian tubercle 

 bacilli have been made to acquire all the characters of those of 

 .avian origin. The method adopted was to place bacilli from 

 human tuberculosis in small collodion sacs containing bouillon, 

 and then to insert each sac in the peritoneal cavity of a fowl. 

 The sacs were left in situ for periods of from four to eight months. 

 They were then removed, cultures were made from their con- 

 tents, fresh sacs were inoculated from these cultures and intro- 

 duced into other fowls. In such conditions the bacilli are 

 subjected only to the tissue juices, the wall of the sac being 

 impervious both to bacilli and to leucocytes, etc. After one 

 sojourn of this kind, and still more so after two, the bacilli are 

 found to have acquired some of the characters of avian tubercle 

 bacilli, but are still non-virulent to fowls. After the third so- 

 journ, however, they have acquired this property, and produce in 

 fowls the same lesion as bacilli derived from avian tuberculosis. 

 It therefore appears that the bacilli of avian tuberculosis are 

 not a distinct and permanent species, but a variety which has 

 been modified by growth in the tissues of the bird. Evidently 

 also there are degrees of this modification according to the 

 period of time during which the bacilli have passed from bird to 



