Volume VII 
No. 4 
MOSQUITOES AND MALARIA. 
A STUDY OF THE RELATION BETWEEN THE NUMBER OF 
MOSQUITOES IN A LOCALITY AND THE MALARIA RATE. 
.By H. WAITE, M.A., B.Sc. 
Professor Ross, in his Report on the Prevention of Malaria in Mauritius*, 
has dealt briefly, from a mathematical point of view, with the influence of 
mosquitoes on malaria and he suggested in a letter to Professor K. Pearson that a 
further treatment from the more mathematical side would be of value. Such is 
the origin of the present investigation and it is to the above-mentioned Report 
that I am entirely indebted for the numerical data upon which this enquiry is 
based. 
It has been proved conclusively that malaria is caused by the bite of 
a mosquito which has already bitten a previously infected person ; and that the 
infection is probably conveyed only by the sub-family of mosquitoes called 
Anophelina. Hence, in order that the disease may spread in a neighbourhood, 
there must be present a source of infection in the shape of persons suffering from 
malaria, and a sufficient number of anophelines to act as carriers. Moreover, 
since recoveries are constantly taking place, it is clear that the increase or 
decrease in the number of cases will depend largely on the relative frequency of 
anophelines and of human beings. 
Malaria Rate. The ratio of the number of persons affected with malaria 
to the total population of a district at a given time is called the Malaria Rate of 
the district at that time. In general, the rate is continually changing owing to 
(a) new infections, (6) recoveries, (c) emigration and immigration, (d) the birth 
and death rates, and (e) the extent to which cases are isolated, as well as owing to 
changes in the mosquito population. 
As emigration and immigration vary considerably in different localities, and in 
the same locality at different times, their influence on the malaria rate cannot be 
* Report on the Prevention of Malaria in Mauritius, by Ronald Ross, D.P.H., F.R.C.S., D.Sc, 
LL.D., F.R.S., C.B., published by Waterlow and Sons, London, 1908. 
Biometrika vii 54 
