An electron microscopic study of amoebae with particular reference to induced pinocytosi

Amoeba proteus was studied in thin sections by means of the electron microscope under normal conditions and after treatment with substances which induce pinocytosis - the ingestion of fluid by invagination of the plasma membrane to form cytoplasmic droplets. The description of the nucleus, cytoplasmic membranes, mitochondria, fat droplets, crystals and Golgi apparatus confirms that already made by others and adds some details. In addition the relationship between volume and surface area of the mitochondrial membranes is examined. The structure of the heavy spherical bodies is described for the first time in the electron microscope. Each consists of a highly electron dense mass believed to contain mineral salts. In support of these findings the closely related giant amoeba Pelomyxa carolinensis was examined after centrifugation in vivo. The structure of the strata produced is described in detail. Centrifugation confirms the fine structure of the heavy spherical bodies and further suggests that the small round cytoplasmic vesicles round In both species represent the alpha particles of light microscopy. The strain of Amoeba proteus used in the investigations is grossly infected with an unid0jiti.fied bacterium which is accompanied by a specific lammellated structured probably of a lipid nature. The complex bacterial vacuoles are described and their general relationships to other structures is discussed. Pinocytosis was induced with alcian blue and a few experiments were also carried out with sodium chloride and albumin. The initial channel formation after alcian blue is accompanied by a definite hitherto undescribed change in cytoplasmic consistency. The cytoplasm becomes granular, and more firmly attached to the plasma membrane. The ingested membrane and the inducer are segregated into complex droplets and there is evidence that the membrane itself is digested. After very intense pinocytosis, the amoebae show signs of toxic effects. Mitochondria become grossly altered, ingested material becomes surrounded by an entirely new membranous structure possibly derived from the cytomembranes and masses of lamellated bodies probably representing phospholipid occur free in the cytoplasm. As a side effect of pinocytosis small fragments of cytoplasm become trapped between two layers of membrane. The phenomenon is referred to as sequestration. The findings in pinocytosis after sodium chloride and albumin induction are largely confirmatory. The relationship between pinocytosis in amoebae and in other cells is briefly discussed.