MALARIA EXPEDITION TO THE GAMBIA 
5 
eighteen inches deep. During their course along the streets they are made deeper in 
order to obtain a good fall until they reach the beach, where some are thirteen feet 
deep and three feet wide. Similar drains from the side streets enter at right angles 
into these drains ; the water from them is discharged into the river by means ot 
sluice gates, which are opened at low tide. Altogether there are about half-a-dozen 
such gates. The construction of the drains varies to a considerable extent. The 
main drains opening into the river are square, flat-bottomed, built of stone, lined 
with cement, and are for the most part impervious. Further in the town the channels 
are built with stone, but some of them are only partially cemented, either the iron-stone 
blocks on the sides or the bed of the drain being uncemented. These channels allow 
the ground-water to percolate into them at certain seasons of the year. Still further 
in the centre of the town the drains become very shallow and are made ot bricks, 
trough-shaped and uncemented. 
Many of the streets have no ' made ' drains as described above, instead, a 
centrally situated trench is dug in the ground, which either discharges into the main 
drain or discharges at the back of the town, directly into the swamp. These trenches 
vary considerably in depth and width, some of them being four feet from the surface 
of the ground. In some of the drains the earth dug out to form the trench is built 
up on either side of it so that the surface of the street falls away from the trench. 
Similar trenches occur round compounds, squares, and in the grounds ot the Europeans. 
They are for the most part choked with grass, or natives walking across from one 
side of the street to the other carry with them sand or debris, converting the drain 
into a series of holes in the centre of the street ; some of them are so choked in 
this way along their course and at their outlets that it is impossible for the contained 
water to escape. At the corners of the principal streets these drains are bridged over 
by low brick arches. In this situation the drain frequently has a stone placed in its 
course or a cemented catch-pit has been constructed ; here water lodges for a consider- 
able period after the rain has ceased. Later on it will be shown how many of these 
drains afford considerable breeding-grounds for mosquitoes. 
Water Supply. — Rain-water is used for drinking purposes by the Europeans, 
and also by some of the native traders. It is gathered from the roof and stored in 
large tanks. Some of these tanks are fitted with good covers, others are not covered 
properly, so that insects, dirt, etc., contaminating the water, obtain an entrance beneath 
the cover of the tank. The best tank seen was one in which the only mode of access 
to the tank was by means of a man-hole at the top, with a heavy, fluted, iron lid, 
difficult of removal. Some of the native traders also collect rain-water in large iron 
boilers or tubs. These are for the most part inadequately covered, or not at all. For 
domestic purposes, water is obtained by the Europeans from wells sunk in their gar- 
dens. The native population of Bathurst obtain water solely from wells. 
The wells of Bathurst are of two types, namely, deep wells and shallow or tub wells. 
