CHAPTER XLIX 



IMMUNITY 



Paul Ehrlich 



Eli MetchnikoS 



Why can some people resist disease successfully and others have 

 very little resistance f What theory of ininnnuty is most generally 

 accepted? Can all people be made immune to disease? 



The ability of the body to resist disease is known as immunity. 

 To-day, when the emphasis is placed on preventive medicine rather 

 than curative, immunity is one of the most important phases of 

 biology. It is a comparatively new science. Two men largely 

 responsible for founding the science of immunity were Eli Metchni- 

 kofl* and Paul Ehrlich. 



Eli Metchnikoff. By 1883, Pasteur and Koch had succeeded 

 in arousing in many scientists an interest in microbes. Metch- 

 nikoff, a Russian naturalist working in Sicily, studied the way 

 sponges and starfish digest their food. In investigating these 

 animals he noticed certain cells moving in their bodies. These 

 wandering cells acted and looked like amoebas. He fed par- 

 ticles of powdered carmine to the transparent larvae of starfish 

 and the wandering cells ingested the particles. INIetchnikoff 

 wondered whether these wandering cells would engulf microbes. 

 He stuck some thorns from a rose bush into the transparent 

 starfish. Masses of the wandering cells crowded around the 



slivers. He concluded that these cells killed invading germs, and 



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