22 MOSQUITO WORK IN KHARTOUM, ETC.

Improvement in the state of the steamers

Examination of Anophelines

Khartoum’s

‘ ‘ endemic index”

ridiculed. This was the more to be regretted as there is no doubt that mosquitoes

can be banished from all the steamers if a little care and trouble were taken.

Mr. Beadnell, of the Geological Survey, carried out these simple methods on the

s.s. u Nubia,” and practically cleared her of mosquitoes, so that for the first time he was able to sleep below in comfort. A great improvement also resulted in the case of the gunboat u Zafir,” in which I went to Dueim and found to be simply swarming with adult Culices and their larvae, while these measures absolutely prevented any mosquitoes breeding out on board the s.s. u Amka during a period of nearly two months, the greater part of which was passed in regions swarming with these winged pests. Latterly, I am glad to say, the engineers have been impressed with the necessity of doing all in their power to aid the brigade. This is the more necessary as it is easy for the steamers to infect the town and thus spoil much of the work done and render it futile. I am certain that this has occurred in many instances for reasons which will be stated.

The men of the brigade also paid some attention to the killing and capturing of adult mosquitoes, but without much success, as most of the Culices live in the wells and are not easily obtained, while it was impossible for the men to go round and catch mosquitoes in Mohammedan households. A good many Ano¬ phelines and Stegomyia were, however, captured, and in the case of the former I made an effort by dissecting the females to determine the proportion harbouring the zygotes of the malarial parasite. As Daniels 1 has pointed out, this method is only of value when the mosquitoes are selected from different houses and places in equal proportion owing to the great variations which occur in this proportion in adjoining houses and at different times. As he says, the number of infected mosquitoes is the real test, and the number of Anophelines that bite a man per hour is also required. Consequently, such examinations as were performed possessed little value, and, indeed, it soon became difficult to secure material, chiefly because, as the result of the brigade work, Anophelines became a rarity. It was a case of killing the geese which laid the necessary, if not the

golden, eggs. Of greater importance was the preservation of specimens of captured eggs, larvae, and pupae of all the genera found, as these proved valuable object lessons to officers and others proceeding up-country. Several have thus learned for the first time to recognise the appearance of the water-stages of the mosquito. Mr. Cross, of the s.s. “ Gordon Pasha,” made a point of bringing back specimens from his trips up the White Nile.

On the whole, Khartoum may be said to have had a moderate u endemic index.” There were not a vast number of malaria-carrying mosquitoes, but there were many people who harboured the malarial parasite and many more suscep¬ tible to infection.

The results of the work of the brigade are interesting and instructive in several directions. In the first place they have shown the distribution of each of the three main genera.

1 Pauiels, “ Laboratory Studies in Tropical Medicine ”