Immunity against pathogenic micro-organisms 147 



Later, Czaplewski^ himself became convinced that his previous 

 negative results would not stand criticism, and Thiltges, in his work 

 already mentioned, when discussing the fowl, was able to confirm the [156] 

 importance of phagocytosis in the defence of the organism of the 

 pigeon against anthrax. He was struck by the difierence between 

 these two species of birds. In the pigeon it was easy for him to 

 prove that in the individuals that succumb to anthrax the phagocytic 

 reaction is very feeble, whilst in those which ultimately resist the 

 bacillus it is very pronounced. Thiltges likewise observed that the 

 blood and blood serum of pigeons when sown in vitro with the 

 anthrax bacillus, manifest only an insignificant bactericidal power, 

 a fact that further warrants him in attributing great importance to 

 phagocytosis in the maintenance of the natural immunity of the 

 pigeon. It is remarkable that, in presence of these facts, it did not 

 occur to the author to ask whether this fundamental difierence in the 

 mechanism of the resistance, which he thought possible in two birds 

 so closely allied as are the pigeon and the fowl, really did exist in 

 nature. I infer that his experiments on the fowl were made before 

 those on the pigeon, and that the difierence in his results depended 

 specially on the fact that he had acquired greater skill in executing 

 his later experiments. 



Having observed that frogs die readily when inoculated with an 

 anthrax bacillus that was adapted to develop at a low temperature, 

 Dieudonne (?.c.) endeavoured to suppress the immunity of the pigeon 

 by using bacilli adapted to a high temperature. But the inoculation 

 of a second generation of the anthrax bacillus, cultivated at 42° C, 

 was borne by five pigeons without inconvenience. Even bacilli 

 that were rendered capable, by cultivation through sixteen genera- 

 tions, of developing at this temperature were not in a condition 

 to kill more than five pigeons out of thirteen inoculated. These 

 attempts to explain immunity as due to the properties of the bacilli 

 rather than to those of the organism of the pigeon, have therefore 

 led to a result very difierent from that anticipated by Dieudoime. 



The pigeon is further of interest to us because of its natural 

 immunity against the bacillus of human tuberculosis. It resists 

 considerable doses of this bacillus, so virulent for man and for the 

 majority of mammals, and even for some birds (canaries and parrots). 

 Dembinski^, studying the mechanism of this immunity, was able to 



1 Ztschr.f. Hyg., Leipzig, 1892, Bd. xii, S. 348. 



2 Ann, de Vlnst. Pasteur, Paris, 1899, t. xiii, p. 426. 



10—2 



