PAEASITES. 



INTRODUCTION. 



No person can derive advantage from the study of parasites 

 unless the subject be approached in a right frame of mind. In 

 other words, the student of helminthology must, as a primary 

 discipline, dispossess himself of all preconceived opinions what- 

 soever, and in an attitude of child-like simplicity seek truth 

 for its own sake. Unless the mind be absolutely free and 

 unfettered it cannot rightly interpret the facts of this peculiar 

 department of biological science. Those students who are 

 nervously anxious to reconcile the conclusions of modern science 

 with the ideas of their forefathers are certain to remain just as 

 ignorant of the true value and significance of nature-teachings 

 as all their fathers were. 



Whether dealing with the external or internal forms, the 

 study of parasites of man and animals is practically one of 

 boundless extent ; and there is probably no department of 

 knowledge, possessing an equal value in relation to the welfare 

 of man and beast, that is so thoroughly misunderstood by those 

 who are directly concerned in the appreciation of its revelations. 

 This has arisen from a total misconception as to cause and 

 effect. Most people, not excluding even the votaries of the 

 healing art, following tradition, regard the internal parasites or 

 entozoa as creatures either directly resulting from certain 

 diseased conditions of their hosts or as organisms which 

 would not have existed if their bearers had been perfectly 

 healthy. Nothing can be more absurd. Such a conclusion is 

 utterly at variance with all logical deduction from known facts. 

 It is, however, quite on a par with multitudes of other popular 



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