INTRODUCTION. 



Parasites are independent organized beings, descended from 

 peculiar animal or vegetable parents, which require, in order that 

 they may be enabled to complete their development, growth, or 

 reproduction, to take up their abode either constantly or tem- 

 porarily in or upon a second animal or vegetable organism of a 

 different kind, from which they also derive their nourishment. 



Human parasites are those which select the human body as 

 this second organism. 



These parasites are usually divided, according to the place 

 to which they attach themselves, and the kingdom of nature 

 (Animal or Vegetable) to which they belong, into animal 

 and vegetable parasites — Epi- and Ento-zoa, and Epi- and Ento- 

 phyta. We shall adopt the division into animal and vege- 

 table parasites, and endeavour to give a natural historical descrip- 

 tion and classification of the different species, leaving it to the 

 reader himself, from the description of the habitation of these 

 creatures, to determine whether those under his consideration be 

 Euto- or Epi-zoa, or Ento- or Epi-phyta. 



The meaning of the term pseudo-parasites is easily understood 

 from the foregoing. These are animals or plants, which, either 

 in a living or dead state, reach the intestinal canal in consequence 

 of impurities in food or drink, or get into the air-passages, or 

 upon the surface of the body ; but, even when this takes place 

 during the life of the animal, can only continue their existence 

 for a short time on the human body, are soon subjected to the 

 laws of organic decomposition, and are never capable of con- 

 tinuing their species there. 



