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sirup until March 2. At this date^ 14 days after the metamorphosis, 

 two of these Stegomyia stung subject A, a Portuguese, who had arrived 

 in Brazil a few days before, and had up to that time never had yellow 

 fever. The subject showed no reaction following this inoculation. 



He was stung again by one of these two mosquitoes (the second 

 having died in the meantime) on the 10th of March, 8 days after the 

 first inoculation. Four days later, March 14, he developed a typical 

 though mild attack of yellow fever. The character of the period of 

 invasion, the vomiting, the pains, the course of the temperature, the 

 icterus, and the progress of convalescence permitted no doubt as to 

 the nature of the disease. 



We deemed it a duty, nevertheless, to confirm our diagnosis experi- 

 mentally. After recovering, this subject was twice submitted to the 

 stings of several Stegomyia infected by a case of yellow fever. He 

 showed himself absolutely refractory to these inoculations, as do all 

 individuals recently immunized by a first attack. 



Let us add that the conditions under which he was observed by us 

 from the time of his arrival in Brazil do not permit that any source 

 of contamination, other than the' hereditarily infected mosquito by 

 which he had been stung, could have brought on the attack of yellow 

 fever which he had presented. 



It may be concluded from this experiment that under conditions 

 which can not as yet be precisely defined the Stegomyia fasciata, the 

 progeny of a mother directly infected by a case of yellow fever, are 

 themselves infected hereditarily. It follows from the various experi- 

 ments done on this subject that the time needed by the mosquito hered- 

 itarily infected to become capable of discharging the virus with its 

 salivary secretion is longer than in the case of the mosquito which has t 

 drawn the virus directly from the blood of a patient. This period 

 was 22 days in the positive case. 



It follows likewise, both from experiments and from epidemiologic 

 facts, that this hereditary transmission can not be considered as the 

 general rule but rather as an exceptional occurrence. 



The mildness of the attack suffered by A warrants the belief that the 

 passage of the virus from one generation of Stegomyia to another is 

 accompanied by a certain amount of attenuation. This may be a new 

 field open to research with reference to vaccination against yellow 

 fever. 



The knowledge of this mode of propagation explains one of the 

 most obscure points in the history of yellow fever, that of the recur- 

 rence of certain epidemics under conditions where a primary case can 

 not be found that is sufficiently recent to explain the infection of the 

 Stegomyia. 



Finally, its importance can not be disregarded from the point of 

 view of prophylaxis. 



O 



