Distribution of Tropical Diseases in Africa. 483 
and in Africa these are found upon the coasts, along the 
rivers, and in the water-logged swampy districts at an alti- 
tude of under 3000 feet. The quotidian and tertian types of 
intermittent fever are the ones most frequently met with. 
The type of fever stands in a definite relation to the intensity 
of the malarial process; thus we find that the tertian type 
prevails in those regions of Tropical Africa where the malarial 
process, although indigenous, is more sparingly produced. 
The frequency of the occurrence of the quotidian type of 
fever, either in endemic areas or in epidemics, is in direct 
proportion to the severity of the process. When an epidemic 
wave of malarial fever passes over a district, the tertian type 
is seen at its outbreak, whereas at the height of an epidemic, 
or whenever it assumes a severe character, the quotidian 
type obtains; and as the outbreak of sickness abates, one 
meets with a return to the types of fever having a longer 
interval between the paroxysms. In the higher latitudes in 
Africa, and also in the higher altitudes, the quartan type of 
fever makes its appearance. 
All races suffer from malaria, although the Negroes suffer 
less from it, always provided that they do not migrate. In 
Africa, as in all parts of the world, strangers suffer more 
severely from it than does the indigenous population. The 
incidence of malaria is, to a certain extent, governed by the 
seasons. In those places where it is endemic, it occurs all 
the year round, but where it is only slightly developed there 
are two maxima, one in spring and one in autumn, and a 
considerable decrease in the disease in the interval. In 
Africa, in the worst malarious regions, the disease is practic- 
ally most rife at the beginning and at the end of the rains. 
The relation which malaria bears to heat is as follows: the 
greater the mean summer temperature (moisture, etc., of 
course being taken into account) the more malaria, the 
amount of malaria decreasing with the mean annual tempera- 
ture of the place. 
The influence of rain or moisture has undoubtedly much 
to do with the production and spread of malaria. With 
reference to the rains, the malarial poison is most virulent 
either when they set in after a long period of heat, or when 
