CHAPTER XXXIV. THE MALARIAL PARASITE. 



1. Mode of Occurrence and Effects. The disease 

 called malaria or ague is an acute or intermittent fever, 

 formerly supposed to be due to pernicious exhalations in 

 the atmosphere of marshy districts (malo, bad; aria, air), 

 but now known to be due to a Protozoan parasite in the 

 blood. This parasite lives in the red blood-corpuscles, 

 and belongs to a group of the Sporozoa called Haemo- 

 sporidia (Jiaima, blood; sporidion, a spore-like body), 

 because they are blood parasites. There are several forms of 

 malarial fever, and it is uncertain how far these are due to 

 different species of the parasite, and how many species of 

 the latter exist. Three chief forms have been distinguished. 

 Laverania malariae, which causes the pernicious malaria 

 of hot countries ; Plasmodium malariae, found in cases of 

 quartan ague ; and Plasmodium vivax, in tertian ague. The 

 characters and life-histories of the three are closely similar. 



2. Schizogony. The minute sporozoites are intro- 

 duced into human blood by the bite of a mosquito of the 

 genus Anopheles. The sporozoite is slender, almost fila- 

 mentous, sharp at both ends, with a thicker central portion 

 containing the nucleus. Within the corpuscle the sporo- 

 zoite becomes rounded in form and forms an amoeboid 

 trophozoite which grows at the expense of the corpuscle 

 until it nearly fills it. The youngest amaebulae are with- 

 out pigment, but contain in fixed and stained preparations 

 a conspicuous vacuole, giving the so-called ring-form of 

 the parasite. At a later stage the vacuole disappears and 

 grains of pigment termed melanin are formed round the 

 nucleus (fig. 207, 6). 



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