ALBERT

Notizen: SYNOPSIS. Merozoites from Plasmodiunz gallinaceum (exoerythrocytic forms) have been observed with the electron microscope in thin sections of infected tissue cultures. When still in segmenter formation, at the end of the intracellular cycle, a small canaliculum can be observed in their proximal part which runs from the nuclear region down into the cytoplasmic core of the segmenter, where, in some sections, it continues directly into the endoplasmic reticulum of the core.Large, vacuole-like empty spaces in the merozoites recall swollen mitochondria. They show short villi at the periphery, instead of the typical cristae; they resemble the mitochondria of starved tissue cells.In the distal pole of the merozoites, one or two oval bodies of great electron density are present, among several smaller granules, both structures still being of unknown significance. The rest of the cytoplasm is of great electron density and shows a fine granulation.In the young trophozoites the oval bodies and the smaller granules disappear. Also, mitochondria are not found just after parasites enter a cell. These, however, reappear soon.The contact of the trophozoites with the cytoplasm of the host is intimate. Both surface membranes of the parasite are visible, mostly intact, but showing also openings which are considered artifacts, since no images have been obtained which indicate a passage of material through them from the host to the parasite. It is believed, however, that the parasite takes up material from the host through the membranes by an osmotic process. The fading of the electron density and the greater distance between the particles of its cytoplasm in the growing parasite seem to prove this. The particles which are responsible for the electron density of the merozoites, and of the young trophozoites, do not differ in their aspect from the RNA particles of the host cells.The nucleus, which in the merozoites and in the very first intracellular stages shows a homogenous fine and dense granulation, develops a darker region later, of irregular shape, which is located eccentrically, and is considered the nucleolus of these forms.