LIFE OF ELIE METCHNIKOFF 169 



which, not being renewed for some time, were missed 

 by the microbes afterwards introduced into the organ- 

 ism, which therefore could not develop completely. 

 Chauveau, on the other hand, thought that, in cases 

 of immunity, the humors contained substances which 

 were unfavourable to microbes. Those theories ex- 

 plained particular facts, but were not applicable to 

 the generality of cases. 



Other theories,^ whilst attributing an active part 

 to the organism itself, failed to account for the 

 mechanism of immunity in general. This was due 

 to the fact that knowledge at that time lacked the 

 two essential elements, i.e. the modifications suffered 

 by the organism which was becoming immunised, and 

 the fate of the microbes in the refractory organism. 



The disappearance of the microbes in the cured 

 or refractory animal had indeed been observed ; ^ the 

 inflammatory reaction of the organism in the course 

 of immunisation had been noted ; ^ microbes had 

 long ago been observed inside the white globules of 

 pus ; * but, either an erroneous interpretation was 

 given to the facts observed, or, rather, the links of 

 causality between those factors failed to be established 

 because they were observed solely in the complicated 

 organism of superior beings. Humoral theories, less 

 easy to test, preserved an appearance of generality 

 and were easily admitted. 



Such was the state of the question when Metchni- 

 koff approached it from a naturalist's point of view. 

 He knew the life of unicellular beings and that of the 

 lower multicellular organisms in their complete sim- 



^ l^aegeli, Biichner, Gravitz. * Chauveau. 



^ Biichner. 



* Hayem, Birsch, Hirschfeld, Klepa, Recklinghausen, Waldeyer, and 

 Virchow. 



