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 larvee, 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 larve, 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. 
“ Tt 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 
