42 
REPORT OF THE MALARIA EXPEDITION. 
unanimously came to tlie conclusion that these operations, if scrupulously prosecuted, promised to 
be successful in that town. The pools — at least during the time when we were there, the 
height of the rainy season — were not very numerous ; and could easily be attacked, at but little 
cost, by any of the measures indicated above. That is, we judged that either if the larvae were 
persistently destroyed, or if the pools were carefully obliterated, the insects might be very largely 
reduced, if not almost exterminated, in the area studied by us [^paragraph 13, Map II.]. It is of 
course impossible to speak with absolute certainty on the point until the experiment has actually 
been tried ; but from all indications we thought this conclusion was a reasonable one. 
Bm even if the operations ultimately prove to be successful in Freetown, it does not follow 
that they will be equally successful elsewhere. The conditions obtaining in Freetown do not 
obtain everywhere ; and we have already pointed out that, owing to the hilly nature of Freetown, 
the pools there are both limited in number and are easy to drain [paragraph 13]. On the other 
hand, the large rainfall in Freetown (163 inches) is favourable to the formation and permanence 
of puddles in that place. 
Judging from our observations, the number of Anopheles puddles in any given locality at 
any one time is likely to depend upon a number of factors, namely, (i) amount and continuity of 
rainfall, (2) humidity of the atmosphere, (3) height of the subsoil water, (4) flatness of the ground, 
(5) porosity of the soil, (6) presence of small fish in surface puddles, (7) use of wells and of pools 
for agriculture, (8) temperature ; and also probably on (9) the chemical nature of the soil, and (10) 
presence of some vegetable food necessary to the larvae or even to the adults. Hence we may 
expect much variation in the number of Anopheles pools in various localities. 
In some tropical countries, as in parts of Assam for instance, vast level areas are almost 
under water during the rains. In such places the larvae may abound everywhere ; unless it 
happens — and the point requires study — that small fish are too plentiful for them. Here it 
will be impossible to drain or fill up the pools. 
Again, in Lagos, Strachan [27] and Fielding-Ould \_Addendum 11.] report that the 
pools are extremely numerous, while the ground is so flat that it will be difficult to drain them. 
In Freetown the pools are much less numerous than in Lagos, and we think it possible 
to attack them with success. 
In Accra, Fielding-Ould did not succeed in finding a single Anopheles pool when he 
was there. 
In Secunderabad, inTndia, only one pool was detected in a considerable area examined 
by one of us — though others might have been overlooked. 
In the Bolan Pass; malaria certainly exists, though the country approximates to a desert. 
In such places pools must be very isolated. 
In Travancore, James reports [29] that the larvae are found in pools used for obtaining 
drinking-water, and also in the submerged plots of ground in which rice is grown (paddy-fields). 
Possibly the larvae may breed in wells — which are often very numerous in tropical cities.* 
Since this was written, Cornwall has described finding Atioplieles larvie in_imused wells in Madras city [30]. 
