INTRODUCTORY 3 



parasitic only in the lower animals. Some are parasitic 

 during a portion only of their existence, whilst others are 

 parasitic in entirely different animals during the different 

 stages of development. 



It is proposed to consider in detail only the protozoa 

 parasitic in man, with brief reference to protozoa parasitic 

 in other animals. 



The knowledge of disease-causing protozoa is advancing 

 so rapidly that some information as to parasites of other 

 animals may at any time become of importance in human 

 pathology. 



The Protozoa are divided into four groups : 



(1) Sarcodina include all forms which move by the 

 protrusion of protoplasm either as blunt and broad pro- 

 cesses or sharp and thin processes. They may be naked 

 or covered in part with shells. Multiplication is by bud- 

 ding or fission ; occasionally spores are formed. 



(2) Mastigophora or Flagellata are provided with motile 

 apparatus specialized for the purpose and consisting of 

 one or more flagella. All parts of the cell enter into the 

 formation of the flagellum. The body is usually of a 

 well-defined shape and covered with a cuticle or mem- 

 brane. Multiplication is by longitudinal fission. 



(3) Sporozoa are unicellular parasites living during a 

 portion of their life in cells and multiplying by the 

 division of the whole or part of the protoplasm into 

 young organisms commonly called " spores," more cor- 

 rectly termed " merozoites." 



(4) Ciliata (Infusoria). The motor apparatus is in the 

 form of cilia which may be either simple or united into 

 membranes. These are formed from the ectosarc only. 

 Reproduction is effected by transverse division or budding. 

 Rarely spores are formed. 



Of these classes it will be convenient to consider first 

 the Sporozoa. 



Researches, especially those of Schaudinn, have gone 

 far to throw doubt on this classification, for his work, if 

 -confirmed, would prove that the distinction between the 



