Electron microscopy of isolated chromosomes

Chromosomes have been isolated from turkey and chicken erythrocytes and from the thymus and liver of the calf by several isolation procedures. Electron microscopy has been used in conjunction with certain chemical and enzyme treatments to determine the organization of the chromosome. Special emphasis has been placed on the use of an electron staining procedure for desoxyribose nucleic acid which has been described by Bretschneider (1). These treatments revealed that the central core of the chromosome consists of a long thin cylindrical structure which has been called the tubule. The tubule is approximately circular with respect to its cross-section and has occasional projections attached to it. The silver staining procedure results in a uniform deposit of silver within the tubule and only after exposure to beams of strong intensity in the electron microscope does localization of silver occur.