178 LIFE OF ELIE METCHNIKOFF 



products. Thus antimicrobian immunity and anti- 

 toxic immunity constitute in most cases two distinct 

 properties. In order to confer antitoxic immunity 

 recourse must be had to vaccination by soluble poisons 

 and toxins. 



Immunity, acquired naturally, is so especially 

 against microbes and not against toxins, for, in nature, 

 it is almost always by microbes that the organism 

 is threatened. As to antitoxic immunity, it is very 

 probably due to the intracellular digestion of toxins 

 by the different macrophages. This hypothesis is 

 supported by the experiments quoted in the pre- 

 ceding chapter. During antitoxic vaccination, the 

 macrophages manufacture, probably at the expense 

 of vaccinal toxins, a certain quantity of antitoxins, 

 substances which offer a great similarity with the 

 fixators. Like them, they are specific ; they are 

 also produced in great quantities and excreted into 

 the humors, which they render antitoxic when suffi- 

 ciently abundant ; finally, they are not very sensitive 

 to high temperatures. That is why, in spite of the 

 impossibility of proving their origin directly, it is 

 quite probable that it is analogous to that of the 

 fixators and that antitoxins are manufactured by 

 cellular elements, the macrophages in particular. For 

 it is they which absorb and digest toxins as well as 

 soluble poisons. 



This deduction is also supported by the antitoxic 

 immunity which may be conferred on unicellular 

 beings in which the cell alone enters into play. 



Phagocytes no doubt manufacture many other 

 soluble ferments corresponding with the elements 

 which they absorb, for, in a vaccinated organism, 

 divers new specific properties of the serum are to be 



