LIFE OF ELIE METCHNIKOFF 163 



The origin of this property must be more recent 

 than that of the phagocytic reaction, for it does not 

 exist in plants or in inferior animals. It was only 

 from superior cold-blooded vertebrates, such as the 

 crocodile — and that only in artificial conditions — and 

 upwards, that Metchnikoff succeeded in finding a 

 specific antitoxic power in the humors. 



He ascertained that the vaccination of animals by 

 toxins conferred, after a time, antitoxic powers to the 

 blood and humors which contained leucocytes. He 

 concluded therefrom that the presence of antitoxins 

 depended on that of the phagocytes. Experiments on 

 divers higher animals having proved that, in them 

 also, antitoxins were localised in humors containing 

 phagocytes, MetchmkofE concluded that the antitoxins 

 were manufactured by the cells themselves. As 

 toxins are absorbed and digested chiefly by macro- 

 phages, it is probable that it is the latter also which 

 manufacture specific antitoxins, or the final product 

 of the digestion of corresponding toxins. Metchni- 

 kofE could only propound this idea as an hypothesis, 

 for the complexity and difficulty of a material demon- 

 stration did not yet allow of a definite solution of the 

 problem. However, certain observations on toxins 

 and antitoxins pleaded in favour of this thesis. 



For instance, working in collaboration with MM. 

 Eoux and Salimbeni, he had found that it is by 

 soluble poisons that the cholera vibrions harm the 

 organism or kill it, but that small doses of the same 

 poisons are vaccines and make the blood of the vac- 

 cinated animal antitoxic. On the other hand, a 

 microbian vaccination is preventive against microbes 

 only but not against toxins and the blood does not 

 become antitoxic. This is explained by the fact that 



