Prophylaxis 539 



4. The premises where such a case has occurred should be fumigated by burn- 

 ing pyrethrum powder (i pound per 1000 cubic feet) to stun the mosquitoes, 

 which fall to the floor and must afterward be swept up and destroyed. 



By these means Major W. C. Gorgas,* without expensive disin- 

 fection and without regard for fomites, has virtually exterminated 

 yellow fever from Havana and from the Canal Zone, Panama, where 

 it was for many years endemic. 



A practical point connected with the screens is given in the 

 work of Rosenau, Parker, Francis, and Beyer,f who found that 

 to be effective the screens must have 20 strands or 19 meshes to 

 the inch. If coarser than this the stegomyia mosquitoes can pass 

 through. 



Reed and Carroll! were the first to filter the blood of yellow 

 fever patients and prove that after it had passed through a Berke- 

 feld filter that kept back Staphylococcus aureus, it still remained 

 infective and capable of producing yellow fever in non-immune 

 human beings. 



This subject was further investigated by Rosenau, Parker, Francis, 

 and Beyer, who found that the virus was even smaller than the 

 first experiment would suggest, as it not only passed through the 

 Berkefeld filter, but also through the Pasteur-Chamberland filter. 

 The filtrates always remained sterile when added to culture-media. 



The virus has not been artificially cultivated. 



Prophylaxis. Guiteras|| has studied the effect of intentionally 

 permitting non-immunes who are to be exposed to the disease to 

 be experimentally infected by being bitten by infected mosquitoes, 

 after which they are at once carefully treated. His first con- 

 clusion was that "the intentional inoculation gives the patient a 

 better chance of recovery," but the danger of death from the ex- 

 perimental infection was later shown to be so great that it had to 

 be abandoned. 



* International Sanitary Congress held at Havana, Cuba, Feb. 16, 1902: 

 Sanitary Department, Havana, series 4. 



t Report of Working Party No. 2, Yellow Fever Institute, Bull. 14, May, 1904. 



t"Am. Med.," Feb. 22, 1902. 



"Bull. No. 14, U. S. Public Health and Marine Hospital Service," Washing- 

 ton, D. C., May, 1904. 



U "Revista de Medicina Tropical," Havana, Cuba, 1902. 



