INSECTS AND DISEASES 395 



enter the red blood corpuscles and grow till they occupy 

 nearly the whole space, and then divide into a number of 

 little spores, which, as the wall of the corpuscle bursts, pass 

 out into the blood. It is at this stage that the chills which 

 characterize malaria occur. These spores enter other cor- 

 puscles and the process is repeated. 



Some of these spores undergo a different kind of develop- 

 ment. When these are sucked up with the blood by a 

 malarial mosquito, they pass through certain stages of de- 

 velopment in the body of the mosquito, and at the end of a 

 little more than a week produce spores of another kind, some 

 of which find their way into the salivary glands. When the 

 insect bites a person, these spores are introduced into the 

 blood of this person together with the fluid from the salivary 

 glands, and begin the process of growth which brings on 

 malaria. Thus it is seen that the relation of the parasite 

 to the mosquito and human beings is a very vital one. It 

 cannot undergo its complete development in either one alone, 

 so that for the continuation of the disease both human beings 

 and this mosquito are essential, one of which must be in- 

 fected with the parasite. 



It has been estimated that the annual financial loss in 

 this country due to the agency of mosquitoes in carrying 

 malaria is $100,000,000. The United States Department of 

 Agriculture has made a study of the economic loss sustained 

 on the southern plantations on account of the sickness and 

 deaths due to malaria. These losses are of two kinds, those 

 due to loss in time and those due to reduced efficiency, at 

 the season of the year when labor is most needed to work 

 and harvest the crops. On one plantation it was estimated 

 that $6500 was lost in one year, $2200 from actual sickness 

 and $4300 from inefficiency due to malaria. 



In 1916, the death rate per 100,000 in the United States 

 was 3. This means that about 3000 people died that year 

 of malaria. These deaths are all due indirectly to mosqui- 



