19

The 19,402 cases examined were composed as follows:—.

(i) British West African pilgrims .. .. 29% (ii) French Sudan (including Wadai, Chad, and

Ubange-Chare) . . .. .. 35% (iii) Sudanese .. . . .. .. .. 36%

The following lists show the number of cases examined at Kosti and El- Dueim respectively for each month of the year together with the number and percentage found infected :—

Month.

Kosti El-Dueim

Total No.

examined

per cent,

infected

Total No. examined

per cent, infected

January . . 1328 20.0 591 20.6 February . . 2206 9.0 327 21.3 March 418 14.0 157 24.7 April 1026 16.0 82 40.2 May .. . f 1134 8.0 85 49.4 June .. .. ,' . . 1824 20.6 115 26.9 July 966 22.0 605 17.7 August .. 1824 20.6 396 26.8 September 1670 19.0 152 38.8 October . . 1700 17.0 92 20.6 November 1110 22.0 150 34.0 December 1171 23.5 273 21.6

TOTAL 16377 19.0

.

3025 24.7

Blue Nile Province.

Sennar Merkaz. Snail Survey. Mature snails were found in the main canal within a week of the re-admission of water. The number of bullinus snails increased until the end of February, after which they gradually diminished until the closing of the canal in April. Snails were found on palm branches inserted along the whole length of the canal. Mature and immature forms were found together, with no preponderance of the latter at any particular season. Spat was also found under similar conditions, but it is probable that little breeding normally takes place in this part of the canal owing to the strength of the current. Bullinus truncatus was the common variety found in the main canal, but bullinus innesii

were also found.

The following is a note by Medical Inspector in charge of the district on the Gebel Moya Hafir, a semi-artificial water storage reservoir :—

“ Six tame ducks were put on the Hafir in December 1927, and were observed to gobble the snails with avidity. The last mature snails were found on February

15th. The water dried up on March 22nd and refilled again in June. The first snails were recovered on July 10th. They were immature and uninfected. The expanse of water was great and all the surrounding country was under water; As the water subsided the snails were found in great numbers. The ducks were replaced on the Hafir on November 4th but the number of snails remained undiminished.

“ Three hundred persons (males) in the vicinity of this Hafir were examined and 10 were found infected.”