(1973) n°3 - Royal Academy for Overseas Sciences

— 513 —
hour. The sporozoites are then inoculated intravenously into
an animal. In human experiments, we felt it was safer to infect
by mosquito bite, although sometime this involved 500 or more
bites on a single occasion.
Another important technical point is the use of a suitable
mosquito vector. For example we went to Borneo a year ago
to carry out experiments on malaria parasites of the orangutan
in order to take advantage of a special colony of A. bala-
bacensis maintained there. This is the species which we thought
would prove to be the best vector. The North American workers
( C o l l in s et al. 1971) in Chamblee, Georgia had previously
shown that it was ideal for the transmission of various « difficult
» malaria parasites, including P. hylobati of the gibbon and
P. brasilianum. I cannot describe the work in detail, but will
only mention that instead of a single species (P. pit bed),
we ( G a r n h a m et al. 1972) found a second and new species
(P. silvaticuvi) in the orang-utan. W e succeeded in transmitting
the latter to a splenectomised chimpanzee which we had taken
with us from England (together with another chimpanzee and
2 Aotus monkeys which failed to become infected), and in
its liver demonstrated the tissue stages of the parasite ( K il l ic k -
K e n d r ic k et al. 1972).
But to go back to the human malaria parasites: W e naturally
wished to complete knowledge of the life cycle of the
two remaining ones — P. ovale and P. malariae, but these
presented problems: P. ovale is rare and P. malariae is notoriously
difficult to get into mosquitoes.
I shall describe the research on P. ovale in a little detail as
it shows the problems we were up against. W e asked the London
and Liverpool Hospitals of Tropical Medicine to look out for P.
ovale and in 1953, received news that a Roman Catholic priest
from Liberia had been admitted into hospital in Liverpool with a
heavy infection of the parasite and was being kept untreated.
Two blood passages were made and some of the blood of the
third patient was sent to London where it was inoculated
intramuscularly into myself. After 13 days, parasitaemia arose
and was accompanied by tertian fever. The blood was watched
for the appearance of gametocytes but few ware produced;
nevertheless, 110 Anopheles atroparvus and A. gambiae were