260 CONSIDERATIONS FROM STUDY OF INSECTS 



But to-day this is changed, and yellow fever is under almost 

 complete control, both here and wherever the mosquito (stegomyia) 

 which carries yellow fever exists. The mosquitoes are prevented 

 from biting persons having yellow fever ; for in this way only can 

 the disease be spread. Drainage and oiling of breeding places, 

 and screening of all windows, are helping to build the Panama 

 Canal. 



The Typhoid Fly a Pest. — The common fly is recognized as a 

 pest the world over. Flies have long been known to spoil food 



through their filthy habits, but 

 it is more recently that the 

 very serious charge of spread 

 of diseases, caused by bacteria, 

 has been laid at their door. 

 In a recent experiment two 

 young men from the Connecti- 

 cut Agricultural Station found 

 that a single fly might carry 

 anywhere from 500 to 6,600,000 

 bacteria, the average number 

 being over 1,200,000. Not all 

 of these germs are harmful, 

 but they might easily include 

 those of typhoid fever, tuber- 

 culosis, summer complaint, and 

 possibly other diseases. A recent pamphlet published by the 

 Merchants' Association in New York city shows that the rapid 

 increase of flies during the summer months has a definite 

 correlation with the increase in the number of cases of summer 

 complaint. Observations in other cities seem to show the 

 increase in number of typhoid cases in the early fall is due, in 

 part at least, to the same cause. It has been estimated that the 

 loss caused from this disease is ' in a single year $350,000,000 in 

 the United States alone. A large part of this loss is indirectly due 

 to the typhoid fly. 



Other Diseases due to Insects. — The bubonic plague, the 

 dreaded scourge of the East, is probably carried to man by fleas. 

 The sleeping sickness of Africa has already been mentioned (page 197) 



-wrmmmmw, 



Showing how flies may spread disease by 

 means of contaminating food. 



