Presented in Figure 2 is a comparison of living cells in culture imaged in both brightfield and phase contrast illumination. The cells are human glial brain tissue grown in monolayer culture bathed with a nutrient medium containing amino acids, vitamins, mineral salts, and fetal calf serum. In brightfield illumination (Figure 2(a)), the cells appear semi-transparent with only highly refractive regions, such as the membrane, nucleus, and unattached cells (rounded or spherical), being visible. When observed using phase contrast optical accessories, the same field of view reveals significantly more structural detail (Figure 2(b)). Cellular attachments become discernable, as does much of the internal structure. In addition, the contrast range is dramatically improved.