248 MOSQUITOES OF NORTH AMERICA 



such outbreaks were due to the presence of infected Stegomyias, and we were 

 obliged to admit that one or several of these mosquitoes had been carried in 

 some way from a distant point where patients existed and from whom they had 

 taken the virus. It is certain that this happened in a number of cases. Never- 

 theless we asked ourselves whether, under certain circumstances, eggs from in- 

 fected Stegomyias, in a locality where there had been an epidemic some months 

 previously, could not give birth to mosquitoes hereditarily infected. 



" Various experiments were made in 1903 to verify this hypothesis. We got 

 the eggs of Stegomyia which had punctured sick people in the first stage of the 

 disease. We raised the larvae, and as soon as the perfect insect issued we made it 

 puncture a human subject. 



" These experiments did not give us at that time any positive result. The 

 subjects who were pierced by such mosquitoes were susceptible to the disease, 

 for it could be given to them later by injections of fresh virulent serum. 



" We began these experiments again in the month of February, 1905. Eggs 

 coming from a Stegomyia twenty days old, which we had caused to puncture 

 several of our patients in order to secure an intense infection, were collected and 

 the larvae, issuing the fourth of February, were placed in a jar for rearing. 

 From the 16th of February the perfect insects began to emerge. These, isolated 

 in tubes from the time of emergence, were fed with glucose up to the second of 

 March. At this date, 14 days after the metamorphosis, two of these Stegomyias 

 punctured subject ' A,' a Portuguese only a few days in Brazil and non-immune. 

 The subject showed no reaction following these punctures. 



" He was punctured again by one of these two mosquitoes (the second had 

 died in the interval) on the 10th of March, eight days after the first puncture. 

 Four days later, the 14th of March, he showed a typical attack, moderately 

 severe, of yellow fever. The character of the onset, the vomiting, the pains, the 

 progress of the temperature, the jaundice, the manner of convalescence, per- 

 mitted no doubt of the nature of the disease. Nevertheless, we tried to confirm 

 our diagnosis experimentally. After the attack we had this subject punctured 

 on two occasions by series of infected Stegomyias. He was absolutely immune 

 to these inoculations, as are all individuals recently immunized by a former 

 attack. Let us add that he was watched by us from his arrival in Brazil, and 

 that the conditions did not permit any contamination other than that through 

 the hereditarily infected mosquito which must have, by its bite, caused the attack 

 of yellow fever which he showed. 



" This experiment seems to indicate that, in the conditions indicated, the 

 Stegomyia fasciata coming from a mother directly infected by a fever patient 

 are themselves hereditarily infected. It results from the different experiments 

 carried out on this subject, that the lapse of time necessary before the hered- 

 itarily infected mosquito may be capable of emitting the virus with its saliva is 

 longer than in the case where the virus has been taken directly by the mosquito 

 from the blood of a yellow-fever patient. This lapse of time was 22 days in our 

 experiment. 



" It results, likewise, from the experiments as well as from the epidemiological 

 facts, that this hereditary transmission can not be considered common, but rather 

 as an exceptional occurrence. 



" The mildness of the attack in this case leads one to believe that the passage 

 of the virus through a generation of Stegomyia is accompanied by a certain 

 degree of attenuation. It opens a new path towards researches in the direction 

 of vaccination against yellow fever. 



"The knowledge of this method of propagation clears up one of the most 

 obscure points in the history of yellow-fever — that of the return of certain epi- 

 demics where no previous case sufficiently recent can be found to explain the 



