618 MAN AS A CONQUEROR 



distinct types. In many cases insects, that are called vectors, pick 

 up the destructive organism incidentally and carry it. Such an 

 insect carrier is the house fly, which has been inveighed against by 

 many writers as being one of our most deadly enemies as a carrier 

 of intestinal diseases. 



Many other insects have criminal records of this sort, for example, 

 the malarial organism is carried by a specific mosquito, Anopheles. 

 Yellow fever is directly related to the Aedes mosquito, while in the 

 Far East another species carries the filarial worm, which causes the 

 terribly deforming disease known as elephantiasis. In certain areas 

 in Africa, the tsetse fly Glossina transmits the dreaded sleeping 

 sickness, and almost universally lice, fleas, ticks, and mites may all 

 be added to the list of organisms responsible for spreading disease. 



Insects that carry parasites dangerous to man's health and welfare 

 maybe divided into two groups, first, casual carriers, such as the house 

 fly, in which the parasite carried has no relation whatever to the life of 

 the insect carrier, and secondly, predatory insects, or those which suck 

 blood, and in which the parasite passes a part of its life cycle. Such 

 insects may often be dangerous carriers, as shown by the blood-sucking 

 mosquitoes that carry malaria and yellow fever. 



Malaria as an Economic Problem 



The economic problem of malaria has been very serious in almost all 

 temperate and tropical parts of the world. In this country, the 

 problem has affected over 13,000,000 of the inhabitants, principally 

 those living in the South, where in some states as high as 90 per 

 cent of the population live in districts where the malarial mosquito 

 is normally found. Statistics in this country show that millions of 

 dollars are lost each year through workers who are incapacitated and 

 whose efficiency is materially affected by the disease. It is estimated 

 that for each death attributable to malaria there is a loss of from 

 2000 to 4000 days by illness. 



Among the effective preventive measures are oiling of standing 

 water to prevent breeding of mosquitoes, draining of marshes, the 

 introduction of certain species of fish which feed upon the larvae, and 

 screening of houses in districts where malaria is present. The most 

 recent method of control is by spraying standing water with finely 

 powdered Paris green. The anopheline larvae eat this material and 

 are poisoned by it. In some parts of Italy where malaria has been 

 extremely prevalent in the past, it was found that towns in areas 



