PREVENTION OF MALARIA 171 
encouraging, and the destruction of anopheles by this means over an area of any size 
in Africa is by no means probable. It soon became evident that, in the rains and in 
swampy districts, anopheles breeding-places were so numerous, so widespread, and 
often so easily overlooked that little could be done under these circumstances. It 
still seemed possible that something might be done in the dry season, when the 
number of pools was often greatly reduced, to influence the number of anopheles in 
the ensuing rainy season. This might have been the case were it not that the life of 
anopheles is often a very lengthy one, and that anopheles often remain months with- 
out any possibility of their having recourse to water for breeding purposes. Late in 
the dry season prolonged search may be necessary before any breeding places are 
discovered in a district, and indeed large areas may not contain a single breeding-place. 
In spite of this adult anopheles are usually to be found in native huts throughout the 
district. The fact is that many thousands of anopheles, which have not originated in 
any pool existing at this time, have remained over (hibernating ?) months after the 
pools they have bred in have disappeared. In spite, then, of the, at first sight, 
promising conditions during the dry season, it is doubtful whether at this time it is 
possible to influence the number of anopheles in the ensuing rains. 
Were it possible generally to make quite sure that all pools in a district were 
regularly treated with culicicides, and were the process kept up for six months or a 
year, it is probable that the results would be most pronounced, and that malaria would 
be much diminished. Unfortunately, in practice such thoroughness is found to be 
very difficult and, out of Europe, almost impossible. 
The Destruction of the Adult Insects. The adult insects can be attacked during 
the day by fumigation of houses. This process carried out systematically must be a 
great adjunct in any scheme of destruction of anopheles. It is a method, however, 
which is only adapted to Europe, and very little could be done in this way in Africa. 
All the methods of combating malaria by destroying anopheles form a power- 
ful means of prophylaxis where considerable labour can be commanded and where the 
area to be rendered free from anopheles is not large. They are quite useless in the 
prevention of malaria in the most deadly of conditions, namely, the up-country stations 
of Africa. As a whole, methods of this class are much more suited to Europe than 
to Africa. 
II THE PROTECTION OF MAN FROM BITES OF ANOPHELES 
As a means of prophylaxis this group is of the greatest importance. 
The experiment carried out by Drs. Sambon and Lowe has shewn that 
enthusiastic men may, in a mosquito-proof house, so effectually exclude anopheles as 
to live in a malarious district without contracting the disease. 
Unfortunately, the effectiveness of these means depends almost entirely upon 
the person employing them. The majority of men in the tropics, either because 
