Light micrograph of a section through a parotid salivary gland. The gland is divided into numerous lobules by connective tissue (blue). Within the lobules are serous secretory cells (pink) that secrete a fluid, saliva, that lubricates the mouth and contains enzymes that start the digestion process. Excretory ducts are white and a blood vessel with red blood cells (erythrocytes, red) is at bottom centre. Two accumulations of lymphocyte white blood cells (purple) are at top. They secrete immunoglobulins, which are part of the body's immune system. The parotid glands are the largest of the salivary glands. In humans, the two parotid glands are just in front of either ear. Magnification: x100 when printed at 15cm tall