YELLOW FEVER EXPEDITION 
53 1 
In considering the last heading, the most striking objective feature is the trans- 
portation of gnats. All ship's captains are agreed that gnats come on board with the 
advent of the lighters, and the men on the tenders complain of the abundance at night 
when lying close to the wharfs. The species found on lighters were ' town ' kinds — 
S. fas data and C.fatigans. 
It may be mentioned here that during my trip up the river to Manaos, all gnats 
which we caught (with the kind assistance of the officers and a fellow-passenger) were 
preserved day by day, and S. fasciata did not occur until the day after arrival off 
Manaos, when ten specimens were taken, presumably they came off the lighters. Only 
other species came on board during the passage. 
Investigation of a number of lighters at Para shewed that S. fasciata larvae were 
present here and there on the bilge of the covered lighters, unfortunately they had 
been recently cleaned out and painted, so that probably the larvae were unusually 
scanty. The open lighters, some of which contained a considerable amount of water, 
were free from larvae ; this was ascribed to the fact that they are used for coal (also 
salt, etc.), and the contained water was covered by a thin film of tarry or oily matter. 
The adult insects, however, would have to become infected ; if this could occur, from 
feeding on the labourers more widely spread and more frequent outbreaks would be 
probable on these ships. It seems more likely that occasional infected gnats might be 
carried from the city in the lighters or steam tenders to the ships. The local conditions 
are such that the mode of transfer of yellow fever by gnats, is highly probable. 
Several cases occurred amongst the persons who brought out steamers for the 
river service ; here, however, the vessels lay close up to the city, and the individuals 
in question were in the habit of spending time on shore, so that no satisfactory evidence 
is afforded of the mode of infection. In all these cases pertaining to ships it is difficult 
to get satisfactory accounts, and, moreover, by the time that reports are received too 
much delay has intervened. 
Nothing very definite is afforded by the following instance of a sailing vessel from 
the point of view of mode of transfer of the fever, but it shews how severely a vessel 
may be attacked about Para : — 
The barque ' CP.' arrived off Para on December 22, 1900, from Antwerp, laden 
with rails and other cargo, such as cement, under the German flag. The captain and 
crew consisted of fourteen persons all told. The vessel lay off the city abreast of it, 
that is, a matter of a few hundred yards distant, until February 4, when she was taken 
alongside the wharf to load with ballast for a week. This and other information was 
o 
kindly given me by the captain. Mosquitoes did not appear on board till about a 
fortnight after arrival, i.e., about 1st of January. (When I visited the ship they were 
appallingly abundant — S. fasciata and C. fatigans). Crew only went on shore with boat 
to return at once, and were never on shore at night. 
