Light microscopy of multinucleated osteoclasts (red) at the surface of bone (green). Osteoclasts are mobile cells that constantly remodel bone by attachment to bone surface where they secrete acid and enzymes to dissolve the bone matrix. Loss of bone is normally compensated by deposition of new bone matrix by osteoblasts. The gaps between osteoclasts and bone where bone is being removed are called Howship's lacunae. Blue tissue is calcifying cartilage. Magnification x150 when printed at 10 cm.