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Distribution.

This disease has been found occurring endemically over large areas in the northern Sudan. In the central Sudan although definite endemic areas occur it is less widely distributed. Proceeding south two infected areas limited in extent are found in the Fung Province on the Blue Nile, and the disease is widely dis¬ seminated in the Nuba Mountains district. Further south still in the Upper Nile Province, although cases are found among Arabs from the north, no indigenous

cases have been found among the negroid natives of the country. Similarly, in the Bahr-el-Ghazal Province no indigenous cases have yet been reported. In the extreme south, indigenous cases both of bilharzia haematobium and bilharzia mansoni have this year for the first time been reported from the Yei district of Mongalla Province, and infected bullinus and planorbis snails have been found in khors in this district. The bullinus snails sent to Khartoum for identification were identified as bullinus brochii.

Distribution of Snails.

On the Blue Nile, bullinus is the common variety although planorbis is also present in considerable numbers.

On the White Nile, planorbis snails are generally greatly in excess of the bullinus varieties. As far south as Renk, both varieties are found in large numbers. At Kaka and Kodok both varieties are to be found, but in diminished quantities.

On the Bahr-el-Zeraf and Bahr-el-Gebel, only planorbis has been found up to date. On Lake No both kinds have been found, but in small numbers.

It is questionable whether the climatic conditions in northern provinces are more favourable to the spread of this disease than is the case in the southern areas, or whether there is some other determining factor to account for the wider prevalence of this disease in the northern areas. It would appear to be most probable that it is purely a question of exposure to infection. The north¬ ern provinces have long been exposed to infection by numerous infected persons coming from Egypt; officials, soldiers, artizans, merchants, and navvies for construction work. The central Sudan has been exposed to infection for a shorter period and to a less degree. The southern Sudan has been very little exposed to infection. It is disquieting to find an endemic area at Yei, as this suggests that various other endemic centres may exist and only await detection.

If the snail hosts of bilharzia are as widely disseminated in the south as in the north, and if other conditions are as favourable to the development of the bilharzia cycle in man and snail, then the fact that intercommunication between the north and the south and between different areas in the south is yearly increasing and the fact that for the greater part of the year lakes, streams and pools are to be found everywhere throughout this area, would seem to render the wide dissemination of this disease in the southern areas almost inevitable.

Berber Province.

No further spread to the irrigation farms to the south of Atbara has taken place, but it has not been possible to free from this disease any of the already- infected farms. Especial efforts have been made to kill off all snails during the

non-watering period—April and May—and it is hoped that considerable progress

will result from these measures. The broken brick work of the sluice gates have been found to be the most populous sheltering places for snails. It is hoped that

these sluice gates will be faced with cement at an early date.

It is noticeablepvhere the intake of pumps is in deep water and at a distance from sand banks and rocks lying under shallow water, very few snails find their way into the canals. It is thought that the entry of snails into the canals would be markedly diminished by extending the intake of the pumps into deep water. This matter is being investigated.