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

— 511 —
parasite is not a true Plasmodium and I transferred it to the
genus Hepatocystis. I had studied the parasite for more than
10 years in Kenya, and had spent the last 4 or 5 years in a
search for its exoerythrocytic stages — and equally for similar
stages in fatal cases of P. falciparum malaria in man. Like all
other investigators, I had mistakenly concentrated attention on
the mesoderm of the skin and organs and particularly on the
cerebral endothelium, where J a m es had suggested to me that
I should find the occult cycle in man in the same way that he
had found it in chicks. He told me when I was on home leave
in 1945: « d o n ’t come back from Africa until you succeed».
The development of the monkey parasite (P. kochï) in the
liver was so remarkable {Fig. 2 & 3) that W e n y o n (to whom
I had sent sections) advised me to return at once to London
to demonstrate the material. W e n y o n stated that if similar
stages were subsequently found in human malaria, then the
mystery of the sporozoite would be solved.
On my return to England, I joined forces with Colonel
Sh o r t t who had started work on P. cynomolgi of Asian
macaques. This parasite is almost identical with human P. vivax.
W e used Anopheles atroparvus as the transmitting agent and
allowed hundreds of infected specimens to bite a monkey which
also received the ground up mosquitoes by intra — peritoneal
injection. The animal was sacrificed 7 days later, and all the
organs were taken for examination. Eventually in the parenchyma
cells of the liver were discovered tissue stages (Fig- 4)
of P. cynomolgi wich closely resembled the early exoerythrocytic
schizonts of P. (— H .) kochi.
Our next step was to repeat the work on a human volunteer
using P. vivax, and with Sir Gordon Covell and Mr. P.G.
S h u t e we ( S h u t e et al. 1945) demonstrated the stages of
the parasite in a biopsy of the liver, taken 8 days after massive
infection of the volunteer by mosquito bites. F a i r l e y ’s (1947)
work on Australian soldiers in the 2nd world war had indicated
that maturation of the sporozoite of P. vivax took precisely
8 days, and this gave us the key to the timing of our biopsies.
Similarly we used his figure of 5 days when we (S h o r t t et
al. 1951) conducted our next experiment on another human
volunteer who was infected with P. falciparum. In this species,