500 IMMUNITY. 



be fully imitated in experiments outside the body. The facts 

 given above with regard to the action of antibacterial serum, 

 show how complicated a matter the bactericidal process may be. 

 Further, in natural immunity a direct killing of the organisms 

 by the fluids of the serum is not necessary. It may be sufficient 

 that their growth is prevented, so that they ultimately die out 

 or are taken up by the phagocytes. 



