Schizonts of all rodent Plasmodium studied (Plasmodium yoelii, P. chabaudi,
P. vinckei) show a characteristic morphology when they are completely matu
re: rounded or slightly elongate merozoites, completely detached from the p
igment mass. At this stage, they are localized principally in the spleen an
d the lungs but, in impression smears of these organs they show two differe
nt aspects. In the spleen, schizonts are either inside the host erythrocyte
or extraglobular but still close to a pigment mass; free merozoites are ra
re. In the lungs, on the contrary, merozoites are often free and dispersed;
electron microscopy showed them to lie against the endothelium. Work by ph
ysiologists has shown the blood circulation in the alveoli to be much slowe
d down. Free merozoites, lined against the endothelium of relatively rigid
capillaries, are in the best possible conditions to make contact with the i
ntact red blood cells. Lungs appear to be the privileged site for the invas
ion of erythrocytes by the merozoites. ((C) Academie des sciences / Elsevie
r, Paris.).