VARIETIES OF TUBERCULOSIS 251 



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 conclusively 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 (v. p. 123) 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 

 sojourn, however, they have acquired this property, and produce 

 in fowls the same lesion as bacilli derived from avian tuber- 

 culosis. 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 

 bird, as in some cases inoculation with tubercle bacilli of avian 

 origin has produced ordinary tubercle nodules in guinea-pigs 

 (Courmont and Dor). It is also interesting to note that 

 Rabinowitch has cultivated tubercle bacilli of the mammalian 

 type from some cases of tuberculosis in parrots kept in con- 

 finement. 



3. Tuberculosis in the Fish. Bataillon, Dubard, and Terre 

 cultivated from a tubercle-like disease in a carp, a bacillus which, 

 in staining reaction and microscopic characters^ closely agrees 

 with the tubercle bacillus. The lesion with which it was 

 associated was an abundant growth of granulation tissue in 

 which numerous giant-cells were present. It forms, however, 

 luxuriant growth at the room temperature, the growth being 

 thick and moist like that of avian tubercle bacilli (Fig. 89, c). 

 Growth does not occur at the body temperature, though by 

 gradual acclimatisation a small amount of growth has been 

 obtained up to 36 C. Furthermore, the organism appears to 



