A Scanning Electron Microscope Study of the Lactating Mammary Gland

The study of internal soft tissue with the scanning electron microscope poses special technical problems of fixation, cleaning, and dehydration (3, 4, 6, 7) . For the dried, prepared tissue to be biologically significant, the surface configurations and interrelationships of its constituent cells must be preserved in a state similar to the way they appear in life . At the same time, the tissue surface, in order to be accessible to scanning, must be washed quite free of any residue of the fluids that normally bathe it. Since tissue fluids contain proteins that are preserved by the same fixatives that preserve cells, these requirements may conflict. The technique to be described here was developed to solve these problems for the study . of changes in the natural, internal surfaces of the mouse mammary gland. It has successfully exposed the free surfaces of cells composing the secretory alveoli, revealing some unexpected configurations as well as features predictable from transmission electron microscopy (2, 8, 9) . The mouse mammary gland in the lactating state is spongelike in appearance by light microscopy. It is composed of a dendritic system of ducts ending in clusters of alveoli ; lumina of alveoli and ducts are at all times filled with milk containing