DESTRUCTION OF MOSQUITOES, ETC. 665 



on the river front and working backwards day by day until the 

 whole town had been explored. They were provided with wide- 

 mouthed bottles for taking samples, and instructed how to proceed. 

 In the afternoons, under the charge of Mr. Newlove, the men again 

 went their rounds, the water collections were re-inspected, and any 

 found to be infected were thoroughly oiled. In the case of wells 

 with an average surface area of 12 to 13 square feet about one 

 pint of crude petroleum was employed per well. 



This amount was probably in excess of that actually required, 

 but by using it a reliable film was obtained. Syringes, though good 

 in the case of pools, were no use for wells, and it was found best to 

 simply pour the oil straight down upon the water, which, as a 

 rule, was found at a depth of from 25 to 30 feet. 



The sheiks of the various districts had orders to see that such 

 " 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. 



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. 



For the sake of argument. Dr. Balfour, to show the benefits of 

 treatment, takes the average number of larvae and pupae in 

 infected water at one thousand, beheved to err on the small side. 

 According to the results obtained there is indicated a total destruct- 

 ion of 222,000 mosquitoes, granting that if left alone all the larvae 

 and pupae would have reached maturity. Nor does that represent 

 in any way the eggs which were checked in their development. 



Again, say that 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 

 suffered enormous depletion. From Kassala, Captain Ensor, 

 D.S.O., with whom I travelled in South Africa, reports a great 

 improvement both as regards mosquitoes and other noxious and 

 annoying insects which pass their larval stages in water. The 

 introduction of sunflower cultivation is suggested at stations in 

 the swamp regions of the White Nile. Apart from its water- 

 absorbing capacities, the sunflower is of great value as an economic 

 product, the oil, seeds and fibre all being useful. It has been 

 successfully cultivated in the previously malarial stretches of the 

 Mississippi Valley, and is known to grow well and rapidly in the 

 Sudan. Whilst on duty en the Suez Canal I had the opportunity 

 of meeting the medical officers accompanying the flotilla taking 

 out the American floating dock to the Philippines, and with them, 



