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The Progress and Diffusion of Plague, Cholera and Yellow Fever 

 throughout the World, 1914-1917. Mljiislry of Health. London, 

 Repts. on Public Health o- Med. Subjects, no. 'A, 1920, 276 pp. 

 Price 7-s. 6^/. 



The title of this publication indicates its contents. 



Leak (W. N .) . On the Improvement of Oiling Fluids for Anti-mosquito 

 Work.— //. Trop. Med. & Hvg., London, xxiv, no. 4, 15th 

 February 1921, i)p. 37 40. 



Paraffin, universally used for oiling as an anti-mosquito measure, 

 is not an ideal film producer, and many attempts have been made to 

 improve on the ordinary film, though no deiuiite modifications are at 

 present largely in use. The admixture of linseed oil appears to have 

 been tried with some success by British troops in Persia, the chief 

 gain being increased permanence. Cotton-seed oil would give an even 

 'more permanent film, but th(^ addition of such oils tends to diminish 

 the spreading power. 



When in Palestine, the author found that the addition of cresol 

 caused paraffin to spread remarkably well on water. An investigation 

 of the substances composing cresol showed castor-oil to be the active 

 factor. No other oil has nearly so marked an effect. If one drop of 

 paraffin will make a film five inches in diameter, on the same surface 

 a similar-sized drop with 1 per cent, castor-oil added will make a film 

 two feet in diameter, the spreachng power being increased about 

 twenty-five times. Paraffin in bulk, when poured on to water, will 

 spread up to a certain point, and then the edges get broken . The castor- 

 oil mixture film retains its continuity very much longer, and its edges 

 appear to retain their power of spreading actively as long as there is 

 space to be covered. On an exceptionally clean surface of water two 

 ounces of paraffin spread over an area of about five yards in diameter. 

 A similar quantity of 1 per cent, mixture in a quarter of an hour had 

 formed an unbroken film 30 yards in diameter, and was still activeh' 

 spreading. 



Castor-oil is ordinarily said to be insoluble in mineral oils, but in a 

 warm climate a mixture up to 2 per cent, can be made that will not 

 separate appreciably in a week, while in a cool climate only about 

 0.5 per cent, will remain suspended for any length of time. Very 

 small additions make a decided difference in the behaviour of the 

 film, as little as one-tenth per cent, producing a very much more active 

 film in every way. 



Perhaps the greatest advantage which such an active film might 

 be expected to show is in the presence of reeds, and this was found to 

 be the case by a practical test. 



The mixture film is not only active, but also extremely tenacious. 

 If the film is broken by a stone being thrown in, the rapidity with which 

 the break is fihed up is remarkable. With a 1 per cent, film moderate 

 breezes wih not cause the breaks often seen at the top of each wave 

 with an ordinary film. The practical value of this tenacity in oiling 

 difficult places is very great. The eventual thickness of a film is, of 

 course, determined by the actual amount of oil allowed per unit of 

 area, provided the oil wih spread evenly. 



The value of this mixture lies in greater economy, greater adapta- 

 bility, and greater certainty of action. The last quality is marked in 

 the presence of dust on the water, in the presence of soap or soapy 



