In search of a versatile virtual person
More than 1,800 years ago, the Greek physician Galen came up with a model for how the human body works. Blood, which he called the "natural spirit," originated in the liver and traveled to all parts of the body through the veins. In the left side of the heart, some of the blood mixed with air from the lungs to make "vital spirit," which flowed to all parts of the body through the arteries. Some of this fluid went to the head, where it was infused with "animal spirit," or consciousness, and then was distributed to the muscles and the senses through a network of hollow nerves.