PREVENTION OF MALARIA 383 



shells, tins, cans, pots, etc., wherever stagnant water readily collects, 

 especially near houses. The larvae of Culex float when at rest on the 

 surface of the water, suspended by their tails and with their heads 

 hanging downward; when disturbed, they wriggle to the bottom. 

 The larvae of Anopheles float flat on the surface like small sticks, and 

 when disturbed they wriggle on the surface with a backward skating 

 movement. The former are usually present in artificial collections 

 of water, such as pots, broken bottles, cans, etc., whilst Anopheles 

 prefer natural collections of water, "chiefly rain-water puddles which 

 do not dry up quickly, or which contain green water-weed. Such 

 being the breeding-places, prevention is simple. Collections of 

 stagnant water must not be permitted. Search must be made for 

 them, vessels must be emptied and puddles brushed out with a 

 broom, and small pools drained and filled in. Water must not be 

 allowed to collect anywhere near the house. Land drainage is an 

 obvious preventive of the first importance. 



Cisterns and similar necessary collections of water may be 

 protected by paraffin or petroleum, for these by lying on the 

 surface of the water prevent the pupae of the mosquito from reaching 

 the surface at the time of transformation. When water is required, 

 it may be drawn off from the bottom of the cistern. The surface of 

 paraffin may be renewed once a fortnight or oftener if necessary. 

 Paraffin (kerosene oil) also acts as a culicicide, destroying the larvae 

 by choking their air tubes. The essential condition in any scheme 

 for the sanitary improvement of a malarious region is that the eggs, 

 larvae, and nymphae of the mosquito should be exterminated in that 

 region. Covering small collections of water with healthy soil, accom- 

 panied by thorough drainage, inasmuch as they remove at the same 

 time both the water and the atmospheric air, the two indispensable 

 elements of mosquito life, are the best preventive methods.* 



2. The Destruction of Mosquitoes. Smoke from a wood fire or 

 damp tobacco leaves, or sulphur, or other gaseous disinfectants may 

 be used for this purpose. Kerosene may be used as recommended 

 above for killing the larvae. Individual mosquitoes should be killed 

 whenever possible. 



3. Avoidance of being 1 Bitten by Mosquitoes. For the protec- 

 tion of the person from attack by mosquitoes, there are a variety of 

 contrivances, from mosquito nets to mosquito-proof houses. Mosquito 

 nettings on the bed should invariably be used in malarious countries. 

 There are several points as to the effectual use of such nets. In the 

 first place, the net should be square, should be hung inside a frame- 

 work, tucked carefully under the mattress all round and not allowed 

 to hang down, and stretched tight so as to allow air to pass in easily. 



* See also Brit. Med. Jour. 1900, vol. i., pp. 300-306 (Celli) ; and 1901, vol. i., 

 pp. 193-203 and p. 240. 



