THE CONQUEST OF THE MOSQUITOES i8i 



With all their care to keep out the "bad air," 

 men went on dying of yellow fever and malaria, 

 but nobody could think of any other cause for 

 so much illness. Panama earned and kept a 

 reputation for being the most unhealthful spot in 

 America. More than three hundred years later, 

 in the time of the French canal diggers, many 

 people still thought that their only chance of 

 preventing these two diseases was to keep their 

 windows closed tight after sunset. And still 

 they died. 



It had been learned that great doses of a bitter 

 medicine called quinine, made from the bark of a 

 South American tree, would help to cure malaria. 

 Yellow fever was a different matter. The only 

 treatment for that was to run away from yellow- 

 fever patients as fast as possible, or to take the 

 disease intentionally, hoping to have a mild case 

 and get it over with. 



A person who has had yellow fever and recovered 

 from it never has it again. The same thing is 

 sometimes true of malaria. Such persons are 

 called immune. Most of the natives of Panama 

 were immune, else they would all have died off 

 long ago. 



Those who came in from othqr countries were 

 not immune. You will remember that the French 

 could not keep enough workmen well to dig the 

 Canal. A third of the men died from yellow 

 fever alone. The governor of Jamaica, where 



