The Use of Colloidal Gold for Studies of Intracellular Exchanges in the Ameba Chaos Chaos

In an earlier study on Chaos chaos, it was found that ferritin can penetrate the nuclear membrane, the outer membrane of the mitochondrion, and the membrane lining the food vacuole, after it has been introduced into the ground cytoplasm by microinjection (1). Other work has shown that ferritin and methylated ferritin can be used to analyze the mechanism of pinocytosis in amebas and to follow some of the changes which take place within the cell during the digestion and assimilation of ingested materials (2). Although ferritin and methylated ferritin have proved useful for exploring intracellular exchanges, the conclusions which can be drawn from work with a single test substance are necessarily limited. The general mechanisms of macromolecular transfers within the cell might be more clearly understood if similar experiments were done with particles of graded size, and with particles having different physical and chemical properties. An ideal tracer substance for studies by electron microscopy of intracellular exchanges should have the following characteristics. The substance should be one which can be prepared in a wide range of particle sizes, say from i0 to 500 A. For a given experiment, it should be possible to prepare particles of nearly uniform size, and the dimensions should be measurable. The particles should