Roberton. — Malaria and Mosquitos. 237 



the air. This fact explains the belief . in many malarious 

 countries that huts on high foundations are healthier than 

 those built closer to the ground, and also the salubrity of 

 villages built on hills rising above malarious plains, a well- 

 known fact exemplified by a striking feature in many parts of 

 Italy, where towns and villages are seen on the hills overlook- 

 ing the level country, where most of the inhabitants ply their 

 vocation as agriculturists. 



Even so cursory a description of the life-history of mos- 

 quitos suggests several means of getting rid of them. Water 

 exposed to air is required for the life of the larvae ; cover tanks 

 or remove pools by efficient drainage and they cannot exist. 

 A suggested method for use in cases where water cannot be 

 removed, where the mosquitos breed in small lakes or on 

 the banks of rivers, is to spray kerosene over the surface of 

 the water. It spreads out in a film, very thin, but sufficient 

 to prevent the larvae obtaining air. The larvae float on the 

 surface with their breathing-tubes above in the air. The 

 kerosene chokes them. The fact that the Anopheles lie quiet 

 during the day in the interior of a house or hut enables them 

 to be killed readily by various vapours. A dwelling can thus 

 be freed from them, and may be kept free by the use of proper 

 netting over doors and windows. These three methods — effi- 

 cient drainage, the use of kerosene on the surface of pools to 

 destroy the larvae, and the killing of the adult by insecticide 

 vapours — are the principal means to be depended on in the 

 destruction of mosquitos. 



We have noticed that it is possible to prevent the infection 

 of mosquitos by destroying the malarial parasite in the human 

 blood. This is done by the use of quinine. Where, how- 

 ever, the population is large, especially among uncivilised 

 peoples, there are difficulties in the way of its employment. 

 The expense would be greater than any Government could 

 well afford. Moreover, natives do not care to take it — it is 

 too unpleasant for them. Among native races also it is very 

 difficult to decide, without examining the blood, which indi- 

 viduals are malarious and which are not. It has been shown 

 in different parts of the world that many of the hosts of the 

 malarial parasite give no outward sign of being ill. Long- 

 continued exposure to the parasite seems to give an immunity 

 from its most apparent evil effects. The children of native 

 races in malarial districts are almost uniformly affected. 

 This has been shown by the observations of a special German 

 Commission which visited Java, New Guinea, and East 

 Africa. Any one of these children may serve as a centre 

 from which the disease may be carried. Hence it is im- 

 portant that Europeans living or travelling in malarious 

 districts should not have his dwelling or pitch his camp in 



