714 INFECTION AND IMMUNITY. 



quito become infected it is necessary for him to 

 feed on yellow-fever blood within the first few 

 days (three days) of the fever. 3. The mosquito 

 can not transfer yellow fever directly and imme- 

 diately from the patient to a non-immune, but it 

 is necessary for a period of not less than twelve 

 days to elapse before he becomes infectious. When 

 this time has been reached the insect continues in- 

 fectious for at least fifty-seven days and probably 

 throughout his life. 4. Yellow fever can not be 

 transferred by "fomites." 5. The subcutaneous in- 

 jection of yellow fever blood into a non-immune 

 produces yellow fever, hence the infecting agent 

 exists in the circulation. 6. The serum of a yel- 

 low fever patient, after being diluted and filtered 

 through a Berkefeld filter (Reed and Carroll) or 

 Chamberland B porcelain filter (Eosenau, Parker, 

 Francis and Beyer) is infectious, hence the in- 

 fecting agent at some stage of its development is 

 very minute, possibly ultramicroscopic. 7. "An 

 attack of yellow fever produced by the bite of a 

 mosquito confers immunity against the subsequent 

 injection of the blood of an individual suffering 

 from the non-experimental form of this disease" 

 (Reed, Carroll and Agramonte). 8. The period of 

 incubation usually is three days, but may vary 

 within the limits of from two to six days. 9. "A 

 house may be said to be infected with yellow fever 

 only when there are present within its walls con- 

 taminated mosquitoes capable of conveying the 

 parasite of the disease." 10. "The spread of yel- 

 low fever can be most effectually controlled by 

 measures directed to the destruction of mosquitoes 

 and the protection of the sick against the bites of 

 these insects." 11. No mosquito other than Stego- 



