256 BACOT: MOSQUITOES AND THE DANGER OF MALARIA.
of three-quarters of a century and that of the mosquitoes on a
period of less than twenty years.
The position that we have now to face is this :—Ague (or,
to give it its modern name Malaria) was dying out during the
latter half of the last century, and at its close the disease was
extremely rare, but a well-authenticated case occurred in Norfolk
during 1897. At the outbreak of the War, the disease, apart
from imported cases, was probably extinct.
The plasmodium which produces malaria in man is never-
passed on, so far as the evidence shows, by the female mosquito
to her offspring, and the existence of the disease depends for its
continuance upon a life-cycle passed partly in the human host
and partly within the body of the adult mosquito.
In highly malarious countries, both Anopheles mosquitoes
and human hosts tolerant of the disease are so numerous that
the possibility of any break in the cycle does not arise.
In other situations (such, for instance, as Northern Europe,
where the disease is nearly at the limit of its range), the contin-
uance of the cycle depends upon three delicately-balanced
factors :—
1. The period during which the temperature is high enough
to allow the plasmodium responsible for the disease to develop
within the body of the mosquito. Within this limit, the survival
of Ague will depend upon—
2. The period during which the organism can linger on
in the system cf its human host, coupled with
3. The prevalence of mosquitoes when any recrudescence,
due to hardship and exposure, occurs.
The factor of temperature is clearly beyond our control,
but the two last factors mentioned are amenable to man's
influence ; and, as we are situated at the very limit of the
range of the disease, it should not be difficult to accomplish
in England what has been done in such a former hotbed of
Malaria as Panama—namely, to control the disease.
The prevention of the infection of mosquitoes when a man
who has had malaria at some previous period has a renewed
attack of fever is difficult, but by no means impossible.
If we had a thoroughly-organised national medical service,
the danger attending such attacks could be minimised, if not
prevented ; but we have not, nor is there any likelihood of such