Cultivation of pure cultures 3. Biochemical tests - including enzymology, genetic characterization 4. Animal inoculation - used to study host specificity and etiology of disease 5. Chromatic aberration results from differential refraction of different wavelengths, corrected by using multilayered lenses of different composition, as well as by using monochromatic light. Spherical aberration is due to differential refraction resulting from curvature of convex lens, corrected by use of planapochromatic lenses.
Contrast is achieved by staining.
Gram stain uses mordant to increase stain affinity in certain bacteria but not others, differentiates on basis of cell wall characteristics. Phase contrast microscopy - Internal components of a live, unstained cell are difficult to distinguish because of the lack of constrast. Advantages to interference methods include study of live material. Scanning tunneling microscope has recently been used to view DNA directly. Atomic force microscopy can be used to study surface features of living cells at extremely high resolution.