502 ' Malaria 



they leave the cells with the saliva, and when the mosquito again 

 bites, enter the warm-blooded host to infect it, if of the appropriate 

 species. 



The whole cycle in the mosquito varies, according to the external 

 temperature, frorti ten days to a fortnight. The mosquito may re- 

 main alive for more than one hundred days, and must bite frequently 

 to satisfy its needs. It remains infective so long as the sporozoits 

 remain in the saliva, which is usually as long as the insect is alive. 

 Here it may be remarked that as it is only the female mosquitoes 

 that bite, it is only by them that the infection can be spread. It is 

 an interesting question, not yet solved, whether any of the sporozoits 

 entering into the mosquito's ovaries can infect its eggs so that a new 

 generation of mosquitoes may be born infective. 



The longer the human infection persists, the greater the number 

 of gametocytes formed, until sometimes in aestivo-autumnal malaria, 

 no schizonts are any longer found, though the blood contains large 

 numbers of gametocytes. In such cases the gametocytes, especially 

 the crescents of aestivo-autumnal fever, but sometimes also those of 

 tertian and quartan fever undergo regressive schizogony, by par- 

 thenogenesis, in the patient's blood, and without fertihzation suddenly 

 break up into spores which enter the red blood-corpuscles and occa- 

 sion a relapse of the infection that had apparently spent itself. 



Diagnosis of Malarial Fever.- — Prior to the discovery of the mala- 

 rial parasites and their relation to paludism any vague febrile 

 process was regarded as "malarial," but with an understanding of the 

 disease based upon its parasitology, they have all been ascribed to 

 other causes, and at present only those accompanied by the presence 

 of malarial parasites in the blood are called "malarial fever." 

 The diagnosis is therefore clinical in that the symptoms point to 

 the infection, and microscopic in that the discovery of the parasite 

 in the blood chnches it. 



In all suspected cases, therefore, the diagnosis hinges upon the 

 discovery of the parasite in the blood, and to find and recognize it 

 is the problem. There are various ways of accomplishing this: 



1. The Examination of Freshly Drawn Blood. — ^A drop from the lob- 

 ule of the ear or from the finger is placed upon a slide, covered, and 

 examined directly with an oil-immersion lens. If rouleaux formation 

 prevents the observation of individual cells, the cover should be 

 pressed upon a few times with a needle, to distribute the corpuscles. 

 The film should be thin enough to enable individual corpuscles to be 

 distinctly seen. The parasites are in the red corpuscles, and accord- 

 ing to their ages will present the appearances later to be described. 

 By this means the Kving motile parasites can be observed to 

 advantage. 



2 . The Examination of Stained Blood Films. — For purposes of diag- 

 nosis this method is to be preferred as the colored parasites are more 

 quickly found than the Hve and uncolored ones. The method of 



