CHAPTER XXIX 

 INSECTS AND DISEASE 



We have already learned (Chapter XXVIII) that insects are 

 the necessary hosts of the parasites that cause some of our worst 

 diseases, and tha t the spread of these diseases depends wholly 

 on the presence of the infected insects. It is only during the 

 present century that the very great importance that insects 

 thus bear to our health has been realized, and many of the most 

 important recent discoveries in medical science have had to do 

 with this relation of insects to some of the common scourges 

 that afflict man or his domestic animals. 



Since it was shown beyond all doubt that malarial fevers 

 depend wholly on the presence of infected mosquitoes (page 

 361), successful efforts have been made to control these insects 

 in some of the places where the disease was most common. 

 As mosquitoes breed only in quiet water the problem of 

 control is not as great as it would at first appear to be, and there 

 is now no reason why almost any community should not rid 

 itself of these disease-bearing pests. In temperate regions 

 malaria is not as fatal as it is in the tropics where it is the cause 

 of one-fourth to one-half of all the sickness. Yet it has been 

 estimated that the annual monetary loss due to sickness from 

 malaria in the United States is many millions of dollars. The 

 suffering and misery, the loss of vitality of young and old, 

 and the death of twelve thousand persons each year, are results 

 of malaria the importance of which cannot, of course, be 

 stated in dollars and cents. 



Almost every day there is an increase in the evidence that 

 shows how dangerous are such common and long tolerated 

 household pests as house-flies and their near relatives, the stable- 

 flies, flesh-flies and others. That these insects do aid in the 

 dissemination of certain of our germ-caused diseases, as typhoid 



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