Dr Stephens, The Prevention of Malaria. 129 



other Europeans living some distance away and so infect them. 

 But the actual condition is a very different one. Europeans are in 

 towns surrounded not by isolated cases of European fever but by 

 thousands of cases of native malaria (parasites and gametes in the 

 blood) and in native villages where Europeans live or sleep the 

 night, every hut may contain children with parasites and in these 

 huts we find a percentage of infected Anopheles reaching occasion- 

 ally as high as 50 °/ - So that the European everywhere is living 

 in the midst of infection. How then can this be avoided ? 



We may consider some of the schemes that have been 

 advocated. 



(a) Destruction of Anopheles larvae by the use of kerosene or 

 tar applied to the pools. Such a procedure can only be of the 

 most limited application and experiments made in Freetown for a 

 period of some months shewed that when the application ceased 

 Anopheles larvae reappeared everywhere. 



(/3) Drainage : rilling up of pools and hollows. 



This method has the great advantage that it is permanent in 

 its results. It is naturally expensive, but it should be used as a 

 subsidiary means whenever possible. In Lagos for instance much 

 might be done by filling up with sand the tracts of oozing water 

 that we have described. 



(7) Construction of mosquito-proof houses. 



These have been made use of in the Roman Campagna with 

 good results, but those who advocate them have little knowledge 

 of the climatic conditions of tropical Africa. Life in such a house 

 would be a terrible experience and sooner or later Anopheles are 

 certain to be found inside. 



(8) Destruction of parasites in their host by the use of 

 quinine (Koch). Even if this method were a certain one, and the 

 experience of the Italians is that it is not, its application to a 

 native population as existing in tropical Africa would be a 

 Herculean task. The eradication of native malaria in a town of 

 50,000 inhabitants or even in a small native village is not a 

 practical measure under existing conditions. 



(e) Segregation of Europeans. 



There fortunately remains a simple and practical means of 

 avoiding this great source of infection. That is the method of 

 segregation. 



We may summarize the conclusions at which we arrived after 

 an examination of several hundred native children. The parasites 

 found were solely of the malignant tertian type. The frequency with 

 which gametes occurred was very striking, and the constant presence 

 of infected Anopheles in native quarters was thus readily explained. 



But when we consider Europeans, the conditions are quite 

 different. Parasites are rarely found except in definite attacks of 



