WHAT IS PHYSICAL LIFE 



enon forms the basis of MetchnikofF s 

 phagocytic or cell-eating theory of im- 

 munity. But some bacteria kill, not by 

 themselves entering the blood but by their 

 first securing a lodgment in some part 

 where they stay, generating a virulent 

 soluble poison which poison, and not the 

 bacilli, is then absorbed into the blood. 

 This is the case with the tetanus or lock- 

 jaw bacillus, and hence a tetanus anti- 

 toxin must save a patient with lockjaw 

 in a different way than by Metchnikoff's 

 phagocytes. With Ehrlich's side chain 

 theory, therefore, our hydra illustration 

 would have to be modified into imagining 

 the chains of nodules on the hydra's arms 

 as themselves shooting out lines of attrac- 

 tion which arrest the poisons as they pass 

 in the blood and draw them in to be in- 

 corporated into the nodule. 



But these lines of attraction must be 

 purely chemical in their nature, or in other 

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