28 MOSQUITO WORK IN KHARTOUM, ETC.

Extent of mosquito destruction

Future operations

As regards the second table it is to be noted that it was found impossible, despite every endeavour, to visit eleven water collections by the time the statistics were made up, owing to the fact that the houses containing them were closed, and the owners absent. There were over thirty such cases, but by the kind help of the Mudir, to whom also my thanks are due for supplying the blank plans, the difficulty was overcome save in these eleven instances. In order to complete the table I have counted six of them as harbouring Culex, which is certainly a very fair proportion, judging from what was found elsewhere under parallel conditions. All these houses were in what may be called the “ Culex ” part of the town. Similarly, in Map No. 3, six unvisited wells are charted, and three of these were considered as being infected. The above figures can only be regarded as being approximately correct, and as only applying to the special times at which the examinations were made. The conditions were constantly altering, as the mosquitoes were driven from well to well, and at the time of writing the state of the town is better than the last figures indicate.1 Still, these statistics serve to show that very considerable progress has been made. For the sake of argument, let us suppose that the average number of larvae and pupae in an infected water was one thousand. This is by no means an absurd figure, indeed, I believe it to err on the small side, but even so, taking the first and third tables, a total destruction of 222,000 mosquitoes is indicated, granting that, if left alone, all the larvae and pupae would have reached maturity. Nor does this represent in any way the eggs which were checked in their development.

Again, say half of the above were females capable of laying from 200 to 400 eggs apiece, a moderate computation, and it will be apparent that the ranks of the winged host have undergone enormous depletion. This is further evidenced by the fact that latterly the infected wells have been found to harbour much smaller

numbers of larvae than was the case at first, and by the experiences of residents and visitors. I admit that such statistics as the above savour of guess work, but they approach the truth, and that truth is instructive and encouraging. I should think that there are few mosquito-ridden towns which could be so completely cleared

as Khartoum, where, as will be evident, the conditions are somewhat specialised.

Such a happy result could, however, only be obtained by increasing the staff of workers, by constant vigilance, more frequent inspections, and bringing Khartoum North into the field of operations. Colonel Penton, the P.M.O. of the Sudan, has now agreed to this being done, so even better results may be looked for in the immediate future, especially as the steamers are to receive special attention. The Manager of the Sudan Development and Exploration Company has signified his willing¬ ness to co-operate in the work of clearing the steamers. Of course if the old type of well were abolished and driven or tube wells substituted, the mosquito would find it very difficult to thrive at all in Khartoum, but such a radical and expensive cure would be neither necessary nor justifiable.

At the time when the Blue Nile was at its highest a considerable tract of land to the south-west of the town was submerged by the dammed up waters of the

In February the percentage infected was 10’4, in March only 9'5. Anophelina had disappeared