TRANSMISSION OF DISEASES BY INSECTS 241 



of the experiments; but a little later, while visiting yellow fever patients 

 in a hospital, was bitten by a mosquito which he deliberately allowed to 

 remain on his hand. Five days later he came down with yellow fever, 

 which caused his death. His life was a sacrifice for the benefit of the 

 human race. 



Yellow Fever Mosquito. The mosquito that transmits this fever 

 is Aedes calopus (Stegomyia fasciata) and no other species is as yet known 

 to be concerned in the disease. A. calopus is limited to warm regions; 

 at a temperature less than 68 F. the eggs do not hatch, and below 62 F. 

 the female does not bite (Reed). The dependence of the insect upon 

 warmth for its development explains the cessation of the disease in New 

 Orleans in December, with a mean temperature of 55.3 F. and in cities 

 farther north when frost comes. In Cuba and Brazil the fever has 

 occurred every month in the year. 



Causes of Yellow Fever. The specific cause of yellow fever has as 

 yet eluded detection and is regarded by many investigators as being 

 ultra-microscopic. The U. S. Commission produced the disease by the 

 injection of blood serum that had been passed through a bacteria-proof 

 filter. Blood from a subject in whom the disease had been produced by 

 transfusion was capable of infecting a third person. 



The weight of evidence indicates that the unknown cause of yellow 

 fever is an organism rather than a toxin. 



Control of Yellow Fever. The preventive measures based upon 

 the facts learned by the U. S. Army Commission were wonderfully suc- 

 cessful. In February, 1901, Major W. C. Gorgas began a campaign to 

 eradicate the disease in Havana. His efforts were directed against 

 mosquitoes. Every case of fever had to be reported promptly to the 

 authorities. Then the patient was isolated and all the rooms in the 

 building and in neighboring houses fumigated and the doors and windows 

 screened. Standing water in which mosquitoes might develop was 

 drained or treated with petroleum and water tanks and barrels were 

 screened. 



In September, 1901, the last case of yellow fever arose in Havana, 

 where the disease had prevailed for 150 years, with an annual mortality 

 of 500 to 1600 or more. Cases are now and then brought into Havana 

 from Mexico, but are treated under screens in the regular hospitals with 

 impunity. 



Yellow Fever in New Orleans. In 1905 the last epidemic of yel- 

 low fever occurred in New Orleans. It might have been checked at its 

 inception had not the authorities adopted a policy of secrecy in regard 

 17 



