530 MALARIAL FEVER 



though the morphological differences described we're slight. 

 Further observations have, however, thrown doubt on this dis- 

 tinction, and the evidence rather goes to show that there is a 

 single species. Opinion also varies as to the cycle of this 

 parasite ; according to some observers it is twenty-four hours, 

 according to others forty-eight hours, though it is generally 

 admitted that variations occur. The fever is often of an 

 irregular type and multiple infection is probably common. 

 Although the question cannot be considered as finally settled, we 

 shall speak of three species of human parasites. The zoological 

 position may be shown by the following scheme, generally 

 followed by English writers, the terminology being chiefly that 

 of Grassi and Feletti : 



Family : H^MAMCEBID^; (Wasielewski). 



Genus I. Haemamoeba. The mature gametes resemble in form the 

 schizonts before segmentation has occurred. 



Species 1. Hceniamceba DanilewsM or halteridium. 

 Parasite of pigeons, crows, etc. 



Species 2. Hccmamceba, relicta or proteosoina. 

 Parasite of sparrows, larks, etc. 



Species 3. ffcemamosba malarice. 



Parasite of quartan fever of man. 



Species 4. Hcemamoeba vivax. 



Parasite of tertian fever of man. 



Genus II. Haemomenas. The gametocytes have a special crescentic 

 form. 



Species : Hcemomenas prcecox. 



Parasiteof malignant orrestivo-autumnalfeverof man. 



In addition there are other species belonging to the same 

 family of blood parasites, which infect frogs, lizards, bats, etc., 

 especially in malarial regions. 



We shall now give the chief distinctive characters of the 

 three human parasites. 



1. Parasite of Quartan Fever. The cycle of development in 

 man is seventy-two hours, and produces pyrexia every third day ; 

 double or triple infection may, however, occur. In fresh speci- 

 mens of blood the outline is more distinct than that of the tertian 

 parasite, and amceboid movement is less marked. Only the 

 smaller forms show movement, and this is not of active character. 

 The infected red corpuscles do not become altered in size or 

 appearance, and the pigment within the parasite is in the form 

 of coarse granules, of dark brown or almost black colour. The 



