MOSQUITO WORK IN KHARTOUM, ETC. 21
depth of from 25 to 30 feet. The Sheiks of the various districts had orders to see that such u trained water was not disturbed for forty-eight hours, after which time the users were allowed to remove the oil and take the water. This length of time amply sufficed, all the larvae and pupae present being killed as shown by repeated investigations.
As a matter of fact the real lethal period was probably from about four to six hours, or even less, but it was deemed advisable to let the oil remain for a time as it has been shown that although mosquito eggs may be laid on such oiled waters they will not undergo further development.1 It was of course impossible to make absolutely certain that these instructions were always faithfully obeyed, but in the great majority of cases the people did as they were told, and any that were refractory were at once reported to the S.M.O., Captain Cummins, who straightway informed the Mudir, and the offenders were promptly brought to their senses. Captain Cummins, indeed, rendered great assistance in the work from an administrative standpoint, and was at all times ready to aid and advise. More recently efforts have been directed to the closing of all unused wells, while, wherever possible, covers have been fixed on those in use and pumps introduced. Special methods were required in special places. In the Palace Gardens pools had to be cleared of reeds and water-weeds, and in some instances were abolished;
Mr. Sillitoe, the head gardener, very kindly assisting the brigade as much as possible.
Fish taken from the Blue Nile were tried both in wells and pools. In the formei they speedily died, the water being too hard for them, but in pools containing river water they proved a success, though after causing the larvae to disappear they too often disappeared themselves, owing to the depredations of natives or aquatic birds. Wherever possible zeers (native water filters) were inspected, and a notice both in English and Arabic was posted in the Sudan Gazette, the official government organ, drawing attention to the role of these earthenware jars as breeding places, and emphasizing the importance of having them emptied and cleaned at least twice in the week. At an early period the steamers were found to be largely infected, especially with the larvae of Stegomyia fas data, and to a less extent by those of Culex fatigans. Anophelines, either as larvae or imagines, have never been met with; but up-country, as will be noted later, the adults are frequently to be seen on board, and may remain as passengers for a considerable period. At first it was decided to use lime for the steamer bilges, but this was said, erroneously I believe, to act upon iron and to be unsuitable. Consequently crude petroleum was recommended, though not so good nor so easily applied. Along with this the periodical emptying of the bilge and fumigation with the sulphur squibs described by Colonel Giles 2 were advised, the latter to get rid of the adult insects. Unfortunately in the case of the steamers familiarity had evidently bred contempt, for, at first, despite the co-operation of the Director of the Steamers and Boats Department, little energy was displayed by the engineers in charge, and the preventive measures were largely ignored, and in some instances even
2 Giles. “ Handbook of Gnats or Mosquitoes ”
Co-operation of military and town authorities
Closing and covering of wells
Treatment of Steamers
1 St. George Gray. Journal of Tropical Medicine, 15/10/03
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