148 



Chapter VI 



prove that the bacilli of human tuberculosis encounter in the organ- 

 ism of the pigeon a very great resistance from the phagocytes, 

 [157] especially from the macrophages. These cells fuse together around 

 masses of bacilli and imprison them within real giant cells or poly- 

 nucleated macrophages (Fig. 21). The microphages in this struggle 

 play only a secondary part, 

 but the resistance offered by 

 the macrophages is a most 

 effective one. Incapable of 

 completely destroying the 

 bacilli, these phagocytes 

 exercise over them an un- 

 favourable influence and 

 prevent them from multi- 

 plying and exhibiting their 

 noxious action. The im- 

 portance of the defence by 

 the macrophages comes out 

 still more clearly when com- 

 pared with what takes place 

 if, instead of the bacillus 

 of human tuberculosis, we 

 inoculate into pigeons the 

 bacillus of avian tubercu- 

 losis. In the latter case 

 the microphages certainly 

 promptly seize the bacilli, 



but being powerless against them they perish, whilst the macrophages 

 only intervene later on and in small numbers. The result is that 

 in the pigeon the avian bacillus becomes generalised in the organism 

 and sets up a fatal tuberculosis. 



It must be admitted, then, that the immunity of the pigeon against 

 the bacillus of human tuberculosis is due to the defence by the 

 macrophages. This conclusion is corroborated by the fact that in 

 the fowl — equally refractory against the same bacillus — there is also 

 observed a very strong macrophagic reaction. 



Nocard\ who for several years has been carrying on studies on 

 the relations between the bacilli of human and avian tuberculosis, 

 conceived the idea of adapting the former to the organism of the 

 * A?m, de VJnst. Pasteur, Paris, 1898, t xn, p. 661. 



Fig. 21. Eeaction of the pliagocytes of the 

 pigeon against the bacilli of human tuber- 

 culosis. 



