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of the channel and the straightening of the banks ; the cutting of new 

 ditches for the drainage of wet areas and borrow-pits ; the filling, 

 draining or oil-spraying of these latter whenever possible ; the cutting 

 of a few broad ditches to allow of the free access of small fish into 

 the fish-pond at all times, irrespective of water-level ; the treatment 

 of artificial containers by the use of nitre-cake, consisting of anhy- 

 drous sodium sulphate and acid sodium sulphate, w^hich is lethal to 

 mosquito larvae and pupae, and prevents the development of ova in 

 a dilution of 1 in 400 ; oiling with a rather heavy black oil, graded 

 by dealers as next below fuel oil, applied by automatic drip-cans and 

 knapsack pump sprayers, this oil forming a film that adheres tightly 

 to ditch banks and is very resistant to evaporation ; the use of a 

 phenol disinfectant larvicide, costing 3«. 4rf. per gallon, in ditches in 

 and near lumber yards where oil could not be used owing to insurance 

 restrictions. In addition weekly routine inspections were made, 

 monthly malaria morbidity reports w^ere drawn up, and educational 

 lectures with stereopticon illustrations were given in churches, schools 

 and other meeting places to both white and coloured people at the 

 beginning of operations, with the result that measures for the suppres- 

 sion of mosquito propagation were enthusiastically received. 



The immediate results of the mosquito-control operations begun 

 in April were made evident by the almost complete absence of all 

 kinds of mosquitos, and then, from May onwards, by the progressive 

 diminution in the incidence of malaria. Complete mosquito control 

 was secured at the end of May, and with the exception of a few Ano- 

 pheles quadrimaculatus taken early in July, following heavy rains, 

 no invasions of more than occasional individual mosquitos were ob- 

 served or reported. 



The cost of the above control measures for the reduction of malaria 

 worked out at about five shillings per head of the population. 



The locality selected for demonstration studies in malaria prevention 

 by the use of screening and quinine under rural conditions was a group 

 of 10 plantations situated in the alluvial lands of south-eastern 

 Arkansas. The less elevated portions consist largely of swamp, as 

 yet uncleared, though the more accessible timber is being steadily 

 removed. The water-level being very close to the surface of the ground, 

 water accumulates in the hollows, resulting in a prolific vegetation 

 and an almost tropical undergrowth. 



As in the urban unit, preliminary operations consisted of a systematic 

 survey, and a census to ascertain general sanitary conditions and the 

 history index of malaria. 



The measures adopted for the prevention of malaria comprised 

 mechanical protection against mosquitos by means of carefully 

 applied screens, and the use of quinine in immunising doses. Both 

 these methods were supplemented by the intensive treatment of 

 carriers with quinine in sterilising doses. 



The 106 families under observation were divided into 3 groups, 

 as follows : — A, screen group in which protection was by means of 

 screening, quinine being administered to proven carriers only ; B, 

 quinine group, in which protection was by means of immunising 

 doses of quinine to all occupants of unscreened houses, together with 

 sterilising doses of quinine to proven carriers ; C, combined screen 

 and quinine group, in which protection was by means of screening 



