MALARIA 513 



Malaria 



Malaria is caused by parasitic protozoa, placed in the 

 genus Plasmodium (Hcemamceba), the credit of the discovery 

 of which must be given to Laveran, who described the 

 parasite as occurring in four phases, viz. (1) spherical 

 bodies, (2) flagellated bodies, (3) crescentic bodies, and 

 (4) segmented or rosette bodies. 



The parasites cannot be cultivated beyond one 

 generation, but inoculation of healthy individuals with 

 the blood of malarial patients reproduces the disease, 

 and the same structures or parasites are found in the blood 

 of these infected persons. Inoculation experiments on all 

 animals except man have proved negative, and in the 

 latter the inoculation must be intravenous. 



In the various forms of malarial fever the parasites have 

 the same general characters, though there are distinct 

 differences between them, by which they can be recog- 

 nised and the type of fever differentiated. In each there 

 is an endo-corporeal cycle within the host, through which 

 the recurrent attacks are developed ; there is also an 

 extra-corporeal cycle of development outside the body of 

 the host, whereby the infection of fresh individuals becomes 

 possible. Each of these cycles needs separate description. 



If the blood of a malarial patient is examined an hour 

 or two before, or at the very commencement of, the febrile 

 paroxysm, the parasite will be recognised as a pale, ill- 

 defined mass of protoplasm within the red corpuscles, of 

 which a variable proportion are infected, the size of the 

 parasite varying in the different types of fever. When 

 some hours old a variable number of blackish pigment- 

 granules of melanin make their appearance. These subse- 

 quently coalesce into smaller groups, and the latter again 

 into one or two larger, more or less centrally disposed, 

 masses. The parasites exhibit more or less amoeboid 



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