MALARIA AND ITS TRANSMISSION n 



practically devoid of malaria, while the central and 

 northern counties, except those parts directly border- 

 ing the Pacific Ocean, all have more or less of the disease. 

 This condition is directly associated with the relative 

 abundance of fresh water and consequently with the 

 relative facility for the breeding of mosquitoes. The 

 relation to irrigation will be touched upon later. 



A very common suggestion to escape malaria is to 

 keep out of the "night air," closing the windows and 

 all openings that might possibly permit the "night 

 air" to enter. This again relates to the night-flying 

 habits of the mosquito. 



In districts in which anti-mosquito campaigns have 

 been waged with vigor there has quickly followed 

 a decrease in malaria, no other precaution having 

 been taken. Thus in the village of Penryn (Cali- 

 fornia) the malaria absences in the public schools 

 during the months of September to December were 

 reduced by 45 per cent in only one season's work. 



The circumstantial evidence against the mosquito 

 (in a broad sense) may be summed up as follows : — 



(1) Malaria exists endemically in districts where 

 mosquitoes are present (all species except the Anoph- 

 elines are eliminated experimentally) ; (2) malaria 

 does not exist endemically where there are no mos- 

 quitoes ; existing cases are without exception traced 

 to a visit on the part of the patient to some part in 

 which mosquitoes of the Anopheline type are found ; 

 (3) persons protecting themselves from mosquito 



