Our Balanced World 543 



Another species of mosquito, the stegomyia, carries yellow 

 fever much as the anopheles carries malaria. For many years 

 yellow fever was a dread disease throughout the tropics. It made 

 Cuba a dangerous and unhealthy place, and was so prevalent in 

 Panama that early attempts to build a canal across the isthmus 

 had to be abandoned because of the many deaths among the work- 

 ers from this disease. 



That yellow fever is spread by a certain kind of mosquito was 

 proved experimentally in Cuba by Drs. Walter Reed, James Car- 

 roll, and Jesse Lazear early in the present century. In the course 

 of the experiments Dr. Lazear took the disease and died, a martyr 

 to science. At once the work of wiping out these mosquitoes was 

 started, and Cuba no longer suffers from yellow fever. 



Profiting by this discovery, Col. Wm. C. Gorgas, Chief Sani- 

 tary Officer of the Panama Canal, performed one of the greatest 

 works of sanitation in history, cleaning up the region so thor- 

 oughly that yellow fever and other tropical diseases were prac- 

 tically wiped out. 



The Common House Fly. Besides being a nuisance, the com- 

 mon house fly is a positive menace to health. It is an enemy to 

 mankind. It is born in filth and delights to live in unclean places 

 from which it brings germs of disease into our homes and deposits 

 them on the food we eat. 



Consider the life history of the fly. The female usually lays 

 eggs in manure piles or on refuse where there is decaying organic 

 matter. Under favorable conditions of temperature the eggs soon 

 hatch into worm-like creatures called maggots. These maggots 

 are greedy eaters. They secure food from the refuse and grow 

 rapidly for a few days ; then they apparently cease their life activi- 

 ties and have a resting period. This is called the pupal stage. 

 A few days more and they develop into adult flies. 



As flies breed very rapidly they soon become exceedingly 

 numerous in warm weather wherever filthy conditions exist. If 

 they stayed where they were born they would not be so dan- 

 gerous. But they do not. In search of warmth or food they 

 make their way into our homes, or else seek the market places 

 where meat and fruit are exposed. Over the food they walk 



