YELLOW FEVER EXPEDITION 
539 
into the city is likely to have yellow fever in mild or severe form first, so that by 
the time he gets malaria he has already acquired yellow fever immunity. There 
does not seem to be any indication of a mutual protecting power between the two 
diseases. 
Stegomyia fas data 
Distribution. Common house mosquito about city and outskirts, as at yellow 
fever hospital, Hospital Santa casa, Marco da legua, Asilo dos alienados (Leper- 
asylum), also at Pinheiro (ten miles down river from Para), and Outeiro. Also on 
vessels and lighters lying off" Para. At Manaos, in many houses about city and 
suburban region ' Cachoeirinha.' Never seen out in forest away from houses, or in 
isolated huts situated away in forest. Not seen at Santa Anna, some twenty-five 
miles north of Para, or Fazenda Natal, in Marajo. 
Breeding Places. Casual waters in vessels, etc., in and about houses such as 
buckets, tins, washtubs, rain gutters, ant-guards (perforated troughs to protect plants 
in gardens, and sugar, etc. in houses), larger and deeper collections of water as casks 
or hogsheads full of rain water. Also in bilge water of barges, lighters, and s.s. 
Viking (Amazon Telegraph Co's ship, many years on the river). Not found in 
sewage collections as cesspools, stable runnings, etc., although found in neighbour- 
hood in cleaner waters. Also not found in natural puddles in forest or streets, etc. 
Habits of Adult. This species in Para is solely a day gnat. It consequently 
afforded means of observation. It is on the wing and will bite shortly after sunrise, 
(about six a.m.); again, a few have been observed biting about eight to nine a.m., 
after which there is a pause till about eleven a.m., when again a few may be feeding. 
The time of chief activity is in the middle of the day, from about twelve to two p.m., 
they then bite freely, and are seen to copulate on the wing in numbers ; another 
pause follows, though there may be a few about, but they do not cause trouble 
when one is sitting at the microscope until about half-past three till about five p.m. 
After dusk or dark I have only once met with a specimen ; this was a male, feeding 
in a sugar-basin rather before seven p.m. These statements are derived from 
observations whilst working in the laboratory, and during a residence for a week in 
the house of a gentleman, whose garden was liberally supplied with ant-guards 
(perforated troughs filled with water, for preventing the access of the destructive 
'Saiiba' to the plants), each of which was full of developing larvae and pupae. 
Sitting in the verandah of this house it was easy to catch fifty to eighty specimens 
without moving from one's chair, in the early hours of the afternoon, yet after sun- 
down, not a single individual was met with. 
In so far as yellow fever infection is associated with this insect, it is of import- 
ance to note this in relation to the common idea that the fever is commonly caught 
at night. It would appear that night would only be dangerous from this insect in so 
