II BIOLOGY AND THE STATE 113 



''educate" them, so that they are able subsequently 

 to resist and eventually to attack and destroy the 

 same jDathogenic Bacterium when present in a stronger 

 and deadly form. This process of education is sug- 

 gested as the rationale of preventive inoculation, the 

 " vaccination " with a modified cultivated growth of 

 poisonous Bacteria acting so as to educate the phago- 

 cytes, and enabling them subsequently to swallow and 

 digest the stronger infective growth. By the training 

 afforded by inoculations with modified virus the phago- 

 cytes are, there is reason to believe, brought into a 

 condition of immunity similar to that which we know 

 the human body can attain in regard to other poisons, 

 such as laudanum, tobacco, and arsenic. It was thus, 

 according to tradition, that Mithridates, King of 

 Pontus, failed at the end of his career to kill himself 

 with poison, having previously in his researches on 

 poisonous agents so saturated himself with them, and 

 habituated himself to their action, that none were 

 deadly for him any more. We may then speak of 

 this training in tolerance of poison as " mithridatism," 

 and refer to the trained phagocytes of an inoculated 

 animal as mithridatised. On the other hand, there 

 are facts with regard to some kinds of infective virus 

 and their appropriate ''vaccins" which lead to the 

 supposition that immunity is conferred, not by the 

 action of weak doses of the "toxin" or actual poison 

 of the virus, but by the action of a distinct chemical 

 substance which exists side by side with the ''toxin." 

 The a23pendix to the paper on Pasteur and Hydro- 

 phobia, p. 166, contains a brief account of this theory. 



I 



