56 
REPORT OF THE MALARIA EXPEDITION. 
the occasion of the slightest rainfall. In this respect the contrast presenteci between Lagos and Accra 
cannot fail to be noticed. Anopheles I found to be so widely distributed that it was impossible for me to 
make any distinction in favour of one part of the town as compared with another. In every native hut 
in all European quarters — in Government House — even in the hospital — I never failed to find some 
specimens. My search for parasites was not equally successful ; for, although I dissected 37 specimens, I 
was only in one able to satisfy myself of the presence of zygotes.* 
During my stay at Lagos there was very little fever; onl}- two cases were admitted into hospital, 
and no out-patients presented themselves for treatment. The blood of both these patients I examined ; 
but no parasites were present, though the examination was made on more than one occasion. This did not 
however surprise me, for both were mild cases, and had been taking large doses of quinine for six days 
before admission. Anophcks caught in the wards, and others "fed" on these same two cases, gave also 
negative results. 
The single specimen in which I found z\gotcs was caught in a native (Hausa) hut; but I 
was unable to trace the cases, and so failed to obtain other specimens. I also, at Lagos, dissected 17 
specimens of Culex ; but, as at Accra, these invariably gave negative results. The problem of how 
best to deal with the Anophcks and their breeding-places is a peculiarly diificult one at Lagos. The 
peculiarities of the soil, and the extreme flatness of the island, render it impossible, in my opinion, for 
drainage to be an effectual solution. For similar reasons, and also on account of the universal prevalence 
of the mosquitoes — Anopheles — it does not seem to me likely that the application of kerosene or tar to 
the puddles will be altogether a successful method. In some few places an attempt has been made to 
drain marshy ground into the lagoons, and occasionally this has no doubt done good ; but, taking the 
town as whole, this is not feasible, and some other method of extermination must be devised. The 
Government, if I may sa)- so, have certainly been acting in the right direction by filling up some of the 
more aggressive mangrove swamps with sand ; but this is necessarily a long and tedious business, and 
at the best, onl}- a portion of the evil can be treated in this way. 
In these swamps, as also at Sierra Leone, I looked for Anopheles, but in neither place did this 
particular genus seem to frequent them. Both drainage, as far as it is possible, and the application of 
kerosene would no doubt do something to improve matters; but until some further measures can be 
de\'ised, the people of Lagos must rely chiefl}- on the general and less direct means that were recommended 
at Sierra Leone, e.g., the intelligent use of mosquito-nets and blinds, etc. — of both of which there is 
at present a surprising absence. 
The "Rest-House," which is used as temporary quarters for Government ofiicials, I found 
swarming with Anopheles; and I was able to obtain particulars of several cases of malarial infection 
occurring there. Before my arrival, and indeed before the mosquito theory had been brought prominently 
forward, several officials dated their fever from nights spent at this " Rest-House " among hosts of what 
everyone recognised as a peculiarly vicious variety of mosquito. I am now referring to several well- 
authenticated cases, the details of which Dr. Strachan is, I believe, about to publish. From a con- 
sideration of these cases one is led to the conclusion that malaria has a definite incubation period of 
from 7 to 2 I days. 
I include here a chart which shows the rainfall, sub-soil water, and fever curves in Lagos for 
twelve months. It will be seen that these curves are as nearl}' as possible coincident, the maximum 
number of fever cases occurring a little later than the point of highest sub-soil water. It is impossible 
to suppose that this is a mere casual coincidence, and that the two curves have not a definite relation to 
one another. The bearing of these observations on the validity of the mosquito theory is obvious, 
for we know that the Anopheles are most prevalent when the sub-soil water is highest. 
It has often been observed in many parts of the world that the upturnings of earth, and 
excavations generally, were accompanied by an increase of malaria : it is certain that the turning up of 
soil will aggravate the manifestations in districts where malaria is permanently endemic. This has also 
* This can be attributeil to the gnats not having become previously infecteil from patients. 
