VI 



SOME INHABITANTS OF MAN AND THEIR 

 MIGRATIONS 



Few people care to confess more than a meagre and second- 

 hand acquaintance with the parasitic worms which inhabit 

 the human body. These slimy, loathsome and repellent 

 creatures, with their subtle and apparently purposeless 

 movements, their insidious and sustained effects upon the 

 well-being of the living community of cells which harbours 

 them, and their innate depravity, constitute in tropical lands 

 at least a veritable " Enemy Within." It is an important 

 part of the sanitarian's duties to keep them under surveillance 

 and to checkmate their activities, for they are a constant 

 menace to the public health. 



Although insignificant in size, number and appearance, 

 some of them are known to have exacted, from the earliest 

 times, a heavy toll from hiunan happiness and progress. 

 Within the past few years, however, new knowledge, acquired 

 not by the physician at the bedside but by the zoologist in 

 the laboratory and in the field, has provided the means whereby 

 the spread of these parasites can be definitely controlled. The 

 chronic and often incurable diseases to which they give rise 

 will eventually be eradicated. 



" From a small text one can preach a large sermon and the 

 proper sermon." One can find in the story of the migrations 

 of this small group of animals alone ample evidence of the 

 very real bearing which the study of animal life has on human 

 progress. 



Several of the worms which Kve in the human body and the 



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