Distribution of Tropical Diseases in Africa. 419 
discharge is only about one thirty-seventh of the rainfall of 
the river’s basin, the African rivers have an abnormal volume 
of discharge, due to the situation of their mouths in the 
equatorial zone, and the excessive rainfall in their catch- 
ment basins. 
The lakes of the African continent may be divided into 
three classes—those situated in the continental axis, namely, 
the Victoria, Albert and Albert Edward Nyanzas, Tanganyika, 
and Lake Nyassa, possessing fresh water, and having an 
oceanic outlet; secondly, Lakes Chad and Negami, which lie 
in continental depressions, and vary greatly in size during 
the various seasons, whose water is more or less saline; and 
lastly, the lakes situated along the course of the great rivers, 
and which are simply enormous expansions of these, caused 
by the heavy rainfall in the Tropics. In Central Africa the 
highest mountains are Kenia and Kilimanjaro in the east, 
and Gambaragara and Ruwensori in the centre, having an 
average altitude of some 19,000 feet. 
Our knowledge of the climatology of Africa, except in 
northern and southern districts, is very incomplete, and this 
is unfortunate, because an exact knowledge of the climatology 
of Central Africa would be of the utmost interest and im- 
portance to us in our present inquiry. It will, however, 
probably be of advantage, before dealing with the climatology 
of distinct areas, which must, of necessity, be treated separ- 
ately, to give a summary of the general phenomena of the 
climate of the whole continent, so far as it is known. 
The mean annual temperature of the continent of Africa 
is high. There is a strip of country upon the east coast 
from lat. 23° N. to lat. 23° S., where the mean annual 
temperature is over 80° F., and the same high temperature 
obtains in two other regions. One of these is towards the 
west of the Red Sea, bounded towards the north by Dongola, 
on the south by Lado on the Nile, on the west by about 
long. 25°, and on the east by Abyssinia and long. 36°. The 
other area is situated towards the west, bounded on the 
south by the coast-line between Sierra Leone and Lagos, 
on the west by long. 17° W., on the east by long. 18° to 20° 
E., on the north by a pyramidal line lowest on the west and 
