Cardiac muscle. Light micrograph of a longitudinal section through cardiac (heart) muscle. The muscle cells each contain one or two elongated nuclei (for example the purple rectangle at upper left) and an extensive, branching cytoplasm (pink), giving the appearance of a continuous network of tissue. Junctions between cells in this network are known as intercalated discs (short vertical pink lines). Here, the electrical resistance of the tissue is low, allowing the rapid spread of electric signals from the heart's pacemaker throughout the muscle. Haematoxylin and eosin stained. Magnification: x130 at 35mm.