1. Monocytes and tissue macrophages become identical in appearance when they live under identical conditions. Macrophages cultivated in nutrient and non-nutrient media acquire different structures. Monocytes and tissue macrophages are mere functional variations of a single type.
2. The structure of the segregation apparatus and of the mitochondria of monocytes and macrophages depends on the composition of the pericellular fluid and on the metabolic state of the cells.
3. The monocyte and the macrophage are endowed with a number of physiological properties which become apparent when they grow in pure cultures.
4. The knowledge of these fundamental characteristics explains the behavior of the cells within the organism.