SECTION XLIX. INSECTS AND HEALTH 



DURING the past few years much has been learned about 

 the part that insects play in the spread of various diseases. 



Flies carry disease. It has been found that flies are 

 frequently very important agents in the spreading of 

 typhoid fever. They do this by carrying t^ human food 

 on their feet or mouth-parts the germs that cause the dis- 

 ease. These germs are brought from the infected mattef 

 which flies visit. This has been proved by allowing a fly 

 which had been on diseased matter to walk across the 

 surface of a specially prepared material in which the germs 

 of the disease could live. In a few days it was found that 

 the typhoid germs were multiplying at every spot the fly 

 had touched. The danger of the spread of such a disease 

 by flies can be decreased as follows: (i) the frequent 

 use of lime where needed about the premises, so as to re- 

 duce the number of flies and thus protect food ; (2) fre- 

 quently cleaning stables and lots to keep flies from breeding 

 there; and (3) thorough screening of houses. 



Mosquitoes and yellow fever. It has been proved very 

 positively that a certain kind of mosquito is the agent 

 in carrying this disease from one person to another. It 

 is probable that it is spread in no other way. This mos- 

 quito is the common black-and-white-banded day mosquito 

 of the Southern states. Before the connection of the 

 mosquito with the spread of this disease became known, 



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