The Tragedy of Tiffany Red.

Tiffany Red was a red blood cell. She lived in the vast expanse of Blood Vessels, and enjoyed frequent trips through the heart.
One day, as she was making her daily rounds to provide organs and other cells with oxygen and nutrients, she caught sight of a handsome white blood cell. He was carousing lazily along when she spotted him. Tiffany gazed in admiration at him. But she couldn't stop. She had a job to do. As she passed through the liver and heart again, all she could think of was the handsome blood cell she had seen.
As Tiffany reached the end of her round, a dreadful cry went up. Some invading bacteria threatened to take the life of the body they all worked for. If the body died, then that would be the end of the blood cells, too.
Tiffany gasped in alarm at the news. She saw a menacing capsule of bacteria making its way towards her. There was no time to redirect her course!
Out of nowhere, the handsome white blood cell she had seen earlier swooped down and killed the bacteria. A great mass of the bacteria's friends rushed at him in anger, but he stood fast. When the invaders had at last been terminated, he engulfed them and toppled over in death.
His self-sacrifice drove Tiffany to tears, and stirred the very nuclei of his comrades.
The Army of the White Blood Cells swore to never forget the brave white cell or the bacteria that destroyed it, and prepared to execute vengeance on the bacteria should they ever return. They never did forget. Always were the antibodies circulating the blood, watching for the moment when they could avenge their brave white blood cell friend.
Tiffany drooped sadly as she carried out her job. The tears had cost her the whole supply of water she had held, and she was caught by the liver on her next round and sent to the spleen for dismantling.

Disclaimer: this is my biology-book's fault. I don't even like learning about anatomy.