Report of the malaria expedition. 
43 
Lastly, ill many places wIktc there is much forest or undergrowth, it may be impos-sibie 
to indicate the pools at all. 
Even in localities where the pools are sufficiently few, it ma\' be difficult to deal with 
them. This will be especially the case with wells, pools of drinking-water, small streams, 
rice-fields, irrigation pools, and pools on water-logged ground. 
On the other hand, operations may be very much facilitated if we can succeed in finding 
a cheap substance, such as was alluded to in the preceding paragrapli, which will prevent the 
insects breeding in the pools. Suppose, for instance, that a ton of sucli a substance will 
suffice to keep a square mile of land free from Anopheles for a whole rainy season, we may 
hope to eradicate malaria from our principal towns at but little cost. 
Again, as suggested in paragraph 17, if Anopheles live from one rainy season to another 
only by continuing to breed in the few pools which remain during the dry season, we may 
then be able to attack them witli comparatively little trouble at that season. This is an indication 
which requires following up. It is difficult to understand how the insects tide over the dry season 
in places in which almost every inch of soil is then subjected to a heat sufficient, one would think, 
to destroy even the eggs. Unless the adults "hibernate," we may suppose that the larvae still live 
in wells, or gardens, or in pools in the bed of watercourses which have nearly dried up. If this 
be the case, operations against the insects may be much facilitated. 
On reviewing these observations, we shall see that - 
(l.) Operations against Anopheles are least likel}- to be effectual in level, water-logged 
localities, and in places where the insects breed in pools which camiot easily be found, or cannot 
easily be treated. 
(2.) Operations will probably be easier in country which is not quite level, or where 
the rainfall is not great. 
(3.) They promise to be very easy in extremely dry places. 
Lastly, it goes without saj-ing that we can scarcely ever expect to deal with Anopheles 
in large rural areas. On the other hand, we may reasonably hope to reduce them, if not to 
exterminate them, in the principal centres of population and civilization that is, in just the places 
where prevention of malaria would be most useful provided alwa)'S that we make intelligent 
and persistent efforts to do so. 
29. Recommendations.— The method of dealing with malaria by operating against. 
Anopheles would seem to have this advantage over the old method by drainage of the soil — it 
promises to be much cheaper. Whereas by the old method we were obliged to drain the whole 
of an infected area — often at great cost -we shall now be called upon to drain, or otherwise deal 
with, only those spots which are the source from which the insects (and, by hypothesis, the disease) 
emanate. 
The fact that drainage has often actually banished malaria now only suggests that drainage 
has often actually banished Anopheles. By reducing this long-known method to one of greater 
precision, we may now reasonably hope to obtain tlie same effect with greater ease. 
