fevers in the army camps during the Spanish- American War reported that 

 "flies swarmed over infected fecal matter in the pits and fed upon the food 

 prepared for the soldiers in the mess tents. In some instances where lime had 

 recently been sprinkled over the contents of the pits, flies with their feet 

 whitened with lime were seen walking over the food." We can readily under- 

 stand why it was that more soldiers were killed by intestinal diseases than by 

 Spanish bullets. 



The fly lays her eggs in manure, or in decaying meat or fish or other gar- 

 bage. She visits also exposed food of all kinds, open wounds on animals, and 

 the excrements of man and other animals. This insect is thus in an excellent 

 position to collect and distribute a varied assortment of bacteria. 



The many species of mosquitoes, which together cover nearly the whole 

 of the habitable earth, have probably always been a nuisance. But now we 

 know that several species are also the sole carriers of various serious diseases, 

 especially malaria and yellow-fever. Moreover, the mosquito is an inter- 

 mediate host of the parasite involved, and not merely a mechanical conveyor, 

 like the fly. 



Fleas appear to be links in a chain that invoK'es man and one of the most 

 dreaded of diseases, the bubonic plague. The specific bacillus that causes this 

 disease was discovered in 1894, but the mode of infection remained unknown 

 until after th^ First World War. The Chinese had long ago noticed that there 

 was some connection between the dying of rats in large numbers and the 

 appearance of the plague. Now scientists know that the disease in men and 

 the plague in rats is caused by the same bacillus, that indeed the parasite is 

 primarily one that lives in the rat. But it is transmitted from rat to rat by 

 fleas, which sometimes get away from dead rats and infect men and women. 

 Here, then, the flea is a simple vector, but rats and other rodents act as breed- 

 ing centers, or reservoirs, of the .parasites. 



How Are Disease-Carriers Exterminated? 



Fighting the Housefly As the horse is gradually removed from our 

 daily lives, opportunities for flies to breed and multiply are reduced. There 

 are still too many about, however, and they are still a menace to health. The 

 individual family cannot protect itself so long as flies are free to breed in 

 neighbors' yards, free to fly through the air, and free to alight on food. 



Whether through a public-health agency or through the intelligent co- 

 operation of all citizens, the fly has to be treated as a community problem. 

 It is necessary to screen or cover all garbage and manure, all stables, and all 

 body discharges that are not immediately removed by suitable sewers or 

 sanitary privies. It is necessary to screen or cover all food, whether for private 

 use or for sale. Every purchaser of food can help the community, as well as 



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