Light micrograph of a section through mammary gland tissue from a lactating woman. Glandular tissue (pink) in the breast has proliferated to produce spaces (alveoli, white) through which milk flows. The glands are arranged into lobules, which are divided by septa (made of collagen fibres, which are stained blue). Each lobule drains into a lactiferous duct that opens to the surface of the nipple. Magnification: x100 when printed at 15cm wide.