u - INTRODUCTION 



delusjpnX Wllj^'hJ in; f:<pife/ef the advance of science, will pro- 

 bably never" become wholly eradicated from the public mind. 

 People who hold these notions either cannot or do not desire 

 to reject a view which has for them a dominating power almost 

 equal to that of any known religious dogma. In conversation 

 I have repeatedly noticed this to be the case. These people are 

 the victims of educated ignorance and they will never allow 

 that parasites are natural developments, accomplishing ends or 

 parts of the orderly mystery which reigns everywhere. Some 

 of them still cling to the creed that the presence of parasites, 

 of internal ones at least, betokens evidence of Divine disfavor ; 

 and their minds are troubled with all sorts of distressing and 

 childish conceptions. In the present age one would have 

 thought that such ridiculous ideas could not be seriously main- 

 tained ; but instead of being relegated to the limbo of similar 

 " old wives' fables " they dominate the opinions of thousands 

 of our so-called educated people. The genuine searcher after 

 truth does not need to be told that all preconceptions of this 

 order hopelessly obscure the mental vision. They operate to 

 render a just and adequate understanding of the science of 

 helminthology impossible. The biologist may say what he lists, 

 but he knows perfectly well that the superstitious mind will 

 continue to ignore the precious and elevating results of scientific 

 research, and that it will perseveringly continue to persuade 

 itself that internal worms, parasites, and entozoa, of whatever 

 kind, belong to the category of " plagues " liable to be dis- 

 tributed as special punishments for human wrong-doing. 



As remarked in my previous treatise, the best way of studying 

 the entozoa is to regard them as collectively forming a peculiar 

 fauna, destined to occupy an equally peculiar territory. That 

 territory is the wide-spread domain of the interior of the bodies 

 of man and animals. Each bearer or " host " may be viewed 

 as a continent, and each part or viscus of his body may be 

 regarded as a district. Each district has its special attractions 

 for particular parasitic forms ; yet, at the same time, neither 

 the district nor the continent are suitable as permanent resting- 

 places for the invader. None of the internal parasites " continue 

 in one stay /' all have a tendency to roam ; migration is the 

 soul of their prosperity ; change of residence the essential of 

 their existence ; whilst a blockade in the interior soon termi- 

 nates in degeneration and death. I repeat it. The entozoa con- 

 stitute a specialised fauna. What our native country is to 



