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Third. In the organs, notably the spleen, of persons dying from 

 malaria. 



Fourth. In the bodies of mosquitoes after feeding on the blood of a 

 malarial fever patient, the insects being kept at a summer heat. 



With the cause definitely recognized, malarial fever may be defined 

 in this wise: 



"A specific infectious disease depending upon the presence in the 

 blood of one or more of several species of closely allied parasites (Haemo- 

 sporidia), which develop within, and at the expense of, tlie red blood 

 corpuscle of the infected individual, resulting, according to the species 

 and number of the parasites present, in more or less periodic febrile 

 paroxysms or in continued fever." 



We may now ask: How does this active cause get into the body? 

 Or, in otlier Avords: How do we catch malaria? 



When the mosquito theory was first announced it was thought that 

 any and all mosquitoes could transmit the disease. It lias since been 

 found that there is only one genus which is now universally suspected. 



There are about 250 species of mosquitoes described, and of this 

 number about 30 have been found in the United States. The genus to 

 which the malaria carrying mosquito belongs is that of Anopheles; it 

 may be recognized by its spotted wings and the peculiar position of the 

 body when at rest— the body axis projecting away from the place of 

 support, as a wall. Our common mosquito belongs to the genus Culex 

 and is considered harmless; it has no spots on the wings and the body 

 axis at rest is parallel to the wall. Anopheles is an inhabitant of the 

 country. Culex lives in the city as well as in the country. 



Mosquitoes normally live on the juices of plants; the sucking of blood 

 is an acquired habit. The females alone suck blood, the mouth-parts 

 of the males are not adapted for it. They seem to survive our winters; 

 they are often to be seen during warm days in the midwinter months. 

 In the spring the few survivors are ready to repopulate all the country 

 around— and at the same time spread malaria. With us malaria is essen- 

 tially a disease of warm weather. 



There are two chief methods by which the subject can be studied: 



First. To search for Anopheles in its usual habitat and then for the 

 malarial fever. Or, 



Second. To find the malarial fever and then look for Anopheles. 



