Galen was particularly interested in blood and its flow throughout the body.
He proved that the arteries contained blood, not an air-like substance called “pneuma,” as had been believed.
His theory was that blood was produced from food intake and that nutrition was supplied to the body from blood flowing in the veins and arteries.
Galen identified the muscles, valves, and main blood channels of the heart, but it wasn’t until 1628 that blood circulation was truly understood.
Galen also made many discoveries about the nervous system.
He learned that all nerves are connected to the brain, many of them through the spinal cord. He cut the spinal cord of animals at different levels and showed which functions were affected.
He proved that the larynx and not the heart was responsible for the voice and that speech originates from the brain.
Galen showed that muscles work together.
For example, the diaphragm and thorax muscles expand the chest to fill the lungs with air. He showed how emotions affected heart rate and health.
He hinted at the idea of genetics by studying how children often have traits of their grandparents rather than their parents.
Like most scholars of his day, Galen spoke both Greek and Latin.
Latin was the language of government, but Greek was still the language of science.