Primary bone marrow macrophages derived from mouse plated on a coverslip and imaged live. Internal Reflection Microscopy (IRM) shows direct apposition of the cells to coverslip with very little depth of field. Note the light gray uniform background extends under the cells' footprints demonstrating that the cells do not adhere tightly to the substrate. At the center of the image is a large polarized lamellipod of a crawling cell. The small spot below the cell is the tip of glass micropipette delivering CSF (colony stimulating factor) locally and the cell may be responding.