CHAPTER XII 

 INSECTS AND HUMAN HEALTH 



I. A TYPICAL GERM DISEASE MALARIA 



Malaria is the most nearly universal of all diseases of man. 

 Not only its immediate effects, but also its after effects have 

 long been considered serious and difficult to control. To-day, 

 however, the course and character of the disease, as well as its 

 cause and the agent by which it is transmitted, are well known 

 and largely under control. This result has been brought about 

 by the research of several men, extending over many years. 

 The story of the investigation is a striking, example of the way 

 in which scientific work is carried on by many individuals to a 

 common end. For this reason malaria may be taken as a type 

 study of the diseases which have been conquered by the use of 

 scientific knowledge. 



254. History of the disease. The downfall of Egypt, 

 which is still mosquito plagued, of Mesopotamia and Athens, 

 and of Rome in a later age, was probably hastened by mosquito- 

 distributed diseases. The people of these countries made use 

 of mosquito netting, brushes, and fans, but they apparently did 

 not connect the mosquito with the diseases which were deci- 

 mating the population. Early in the eighteenth century gnats 

 or mosquitoes were supposed to have some share in the distri- 

 bution of " marsh diseases," by carrying the " miasmic or 

 malarial " poison and injecting it through their sharp beaks 

 into human beings and animals. The poisonous matter was 

 imagined by some to be animalculse, or microorganisms as we 

 should call them to-day. This idea received no support in 

 science until nearly the end of the nineteenth century. 



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