Who were Hippocrates and Galen?

Hippocrates is seen as the Father of Medicine, as he is the oldest Greek doctor whose writings we still have.

Galen is the most famous Greek doctor of the ancient past, probably because his work on digestion dominated medicine for fourteen centuries.

How was digestion first illustrated?

According to Galen, the stomach cooks food. It is helped by the liver which surrounds it and warms it up. Food then passes from the intestine into the liver to be turned into blood. The veins then carry the blood to the different parts of the body.