Immunity against pathogenic micro-organisms 149 



fowl. With this object he enclosed a culture of the bacillus of [158] 

 human tuberculosis in a sac of collodion which he then introduced 

 into the peritoneal cavity of fowls. Under these conditions the 

 bacillus, protected against the aggression of phagocytes, continued 

 to live inside the sac through whose walls the fluid part of the 

 peritoneal lymph could diffuse. After several passages from sac to 

 sac the human bacillus becomes acclimatised to the body of the fowl 

 and is transformed into a variety quite comparable to the bacillus 

 of avian tuberculosis. This experiment has definitely settled the 

 question so long under discussion of the specific difference between 

 the two tubercle bacilli. It has resolved it in the sense of affirming 

 their unity; the avian bacillus is only a modified race of the same 

 bacillus which sets up tuberculosis in man and other mammals. 



In spite of the great difference between the anthrax bacillus and 

 that of human tuberculosis, the immunity against these two bacteria, 

 which is shown in birds, depends in every case upon the reaction of 

 the phagocytic system. 



Having rapidly glanced at natural immunity as we ascend the 

 scale of the animal series we now come to it as it presents itself in 

 the highest class, Mammals, a question on which it is necessary to 

 dwell at greater length because of its great importance, and also 

 because of the fuller study that has been given to it. 



As the immunity of the Invertebrata and of the lower Vertebrata 

 against the anthrax bacillus has furnished us with several important 

 indications we will first endeavour to throw light on the mechanism 

 of the resistance offered to anthrax by certain mammals. The repre- 

 sentatives of this class being, however, for the most part extremely 

 susceptible to this disease, examples of true natural immunity are 

 very rare. The first place among resistant mammals is occupied by 

 the dog. Although young dogs, as demonstrated by Strauss 1 , readily 

 take fatal anthrax, the canine species may nevertheless be regarded 

 as possessing a real immunity, as adult dogs withstand, without 

 inconvenience, the inoculation of large quantities of bacilli. When 

 introduced beneath the skin these bacilli excite a local inflammation, 

 accompanied by a very marked diapedesis of white corpuscles which at 

 once begin to devour the bacilli. This phagocytosis has already been 

 observed by Hess 2 , Malm 3 , myself, and several other investigators, [159] 



1 Arch, de med. exper. et danat. path., Paris, 1889, 1. 1, p. 325. 



2 VirchrjvJs Archiv, Berlin, 18S7, Bd. cix, S. 365. 



3 Ann. de llnst. Pasteur, Paris, 1890, t. iv, p. 520. 



