If you get cut, you’ll almost certainly bleed.
That’s about as much as ancient Sumerians knew about blood. The Sumerians lived around 5000 B.C., a time long before microscopes and modern medicine, so most of what they knew (or thought they knew) came from observations of the outer body.
An Egyptian genius named Imhotep made a big breakthrough right around 3000 B.C., when he realized that blood moves. Somehow, he also concluded that the heart is the organ that makes blood move. It’s a simple idea, but it took scientists another 5,000 years to figure out how the circulatory system really functions. Even today, scientists are still searching for answers about blood.
