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 °/ 0 . 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. 
(A) Drainage : filling 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 
