y2 DISEASES DUE TO PROTOZOA 



(2) Malarial fever is invariably associated with one of these 



parasites at some time of its course or another. 



(3) The phases of a malarial fever bear a definite relation to the 



phases of the life-cycle of the particular parasite present in 

 the blood. 



(4) The characteristic pigmentation of the viscera is fully 



accounted for by the pigment-forming property of the 

 parasite. 

 (5) Injections of malaria-infected blood will, after an incubation 

 of twelve days, be followed by an attack of malarial fever, 

 and similar parasites can be recovered from the blood as 

 those injected. 



(6) The administration of quinine will clear up the clinical 



symptoms, and cause the disappearance of the symptoms in 

 the majority of cases. 



(7) If certain species of mosquito which have fed on infected 



blood be dissected at intervals, the evolution of the parasite 

 can be followed out. 



(8) Mosquitoes thus fed, if kept for a Aveek, will, on biting an 



uninfected man, produce, after incubation, a typical malarial 

 attack. Infected mosquitoes from Rome sent to London 

 were allowed to bite the son of Sir Patrick Manson. A 

 tvpical malarial attack followed. 



(9) If the non-immune is effectively protected against the mos- 



quito bite he will not contract malarial fever, though living 



in a malarial country. 

 Three factors are necessary for an attack of malarial fever : — 

 (i) The malarial parasite. 



(2) The necessary mosquito. 



(3) The non-immune man. 



If onlv two of these factors are present malaria cannot exist. 



THE PARASITE. 



Three parasites have been mentioned, but some believe there are 

 others which cause a quotidian form of the fever, but sucli have not 

 been conclusively demonstrated. 



None of these parasites have ever been found free in air, water, soil 

 or decaying vegetation. 



The three parasites enter the human body as sporozoites, passing 

 from the salivary glands and the hypopharyngeal canal of tjie mosquito 

 into human blood at the time of the bite. 



One mosquito, when biting an infected person, may take up from 

 6,000 — 7,000 crescents per cmm. of blood, but they may all perish by 

 phagocytosis in the intestine of the fly. 



