202 PARASITISM 



It is not our purpose here to examine deeply into the secrets of 

 immunity- -the magnitude of the subject forbids anything more 

 than the briefest exposition of the phenomenon of physiological 

 adaptation, which immunity suggests. What this phenomenon 

 means to the organism can be imagined, when the same indi- 

 vidual becomes successively immunized to chicken-pox, whoop- 

 ing cough, measles, mumps, smallpox, and half a dozen other 

 diseases. The fact of minute reactions bringing about great 

 adaptations against disease is only one more instance of the 

 marvelous powers of adaptation which protoplasm manifests. 



