Final stage of maturation of the erythrocytic schizonts of rodent Plasmodium in the lungs

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.).