PROBLEMS IN HOST-PARASITE RELATIONS 



the field of public health since whole communities may 

 be protected as a result of these scientific investigations. 

 In addition there is always before us the possibility 

 of throwing light on the greatest of all of our problems, 

 that of the origin and evolution of parasitism. The mate- 

 rials available for observation and experiment are par- 

 ticularly favorable for attacks on this problem, and as 

 an added incentive is the knowledge that the elucidation 

 of the changes that occur during the development of the 

 parasitic from the free-living habit may furnish the key 

 to the solution of the problem of the method of evolution. 



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