12 MALARIA 



bites while dwelling in malarial districts (otherwise 

 living as do the natives) do not contract malaria ; 

 (4) communities previously noted for malaria have 

 been practically freed from this disease when efficient 

 sewer systems have been installed ; (5) properly 

 conducted mosquito crusades result in the elimination 

 of nearly 50 per cent of the cases of malaria within the 

 district in the same season (the occurring cases can 

 be accounted for through relapses and exposure to 

 mosquito bites outside the protected districts). 



It should furthermore be said that malaria may be 

 wholly absent even when there is an abundance of 

 mosquitoes. In answer to this it should be explained 

 that there are several hundred species of mosquitoes, 

 of which number only two or three for any one 

 locality are capable of transmitting malaria. Hence, 

 first, the mosquitoes in such localities are, probably 

 all non-malaria bearing or Culicine, with entire ab- 

 sence of the malaria bearing species (Anopheline) ; 

 or, secondly, if Anopheline mosquitoes are present, 

 they have not become infected by the importation of 

 persons affected with malaria, i.e. malaria must first 

 be introduced before the Anopheline mosquitoes can 

 carry it from person to person. 



Experimental Evidence. — As is noted under the next 

 head, malaria is a parasitic disease caused by a blood- 

 inhabiting unicellular animal organism discovered by 

 Laveran in 1880. This parasite, as far as is known, 

 perishes very quickly when taken from the human 



