14 GEOGRAPHY [ No. 98 Among the negro population leprosy , bronchial com plaints, pneumonia, and various tropical diseases, such as guinea -worm , are common , but sleeping sickness, though a few cases have occurred in the extreme south, has not yet obtained a foothold in the Sudan. Venereal diseases have been imported from the north , and are common near the Government posts . A peculiar in fectious disease called kala azar exists in the east, its range extending southwards from Kassala to about 10° north latitude, and west to about 33° 30' east longi It is characterised by fever and wasting, and appears to be spread by vermin . The natives are chiefly liable to attack, though Europeans are warned against sitting or sleeping in native huts in the infected areas .

The chief scourge of the Arabs is syphilis, especially in Kordofan . Smallpox, which formerly broke out at intervals with great virulence, is now much diminished .

Cerebro -spinal fever, however, still gives trouble, a severe epidemic having occurred in 1915.

tude .

(5) RACE AND LANGUAGE Race The wealth of the Nile valley has made the Sudan from earliest times peculiarly liable to invasion; hence the original stocks have been overlaid by successive waves of immigrants, and the countryis now a Babel of numerous races andtongues . The principal incursions have been those of black races from south and west, and of Arabs from the east . These have intermarried with and frequently been absorbed by the aboriginal popula tion , the result being a mixture of races which makes classification unusually difficult. Speaking generally, the desert zone in the north is now peopled by nomadic Hamites and Arabs, the centralregion by Arabs, , , Nubas, and negroids, the tropical belt south of the twelfth parallelby negroes. The change of type, how