How did ancient Greece begin to study human blood?

The ancient Greek doctors abandoned the medicine and magical treatment of ghosts and gods, and built their knowledge on the observation of nature and the accumulation of experience. Empedocles, a famous ancient Greek philosopher and doctor, believed that blood was the carrier of animal heat and life. The body fluid theory established by Hippocrates, a famous ancient Greek doctor, became the most important medical theory at that time. He believes that the human body has four kinds of body fluids, namely blood, mucus, yellow bile and black bile. People are healthy when all kinds of body fluids are properly matched. If a certain body fluid is too much or too little, or separated from other body fluids, it will cause diseases.

In ancient Greek medicine, "body fluid" refers to various body fluids flowing in the lumen of human body. Before the invention of microscopes and other instruments to detect the structure and function of the body, these body fluids in the human body were the most easily seen substances in the body. According to past experience, it is easy to attribute the characteristics of life at least in part to these body fluids. If blood is regarded as an important indicator of life, excessive blood loss will lead to the loss of life. Doctors can judge the possible causes of patients according to the changes of human body fluids.

The understanding of blood in ancient Greek medicine was quite vague, and it was usually only in the case of disease that this necessary body fluid existed in the body. Although doctors in ancient Greece have been arguing whether blood itself is more or one of its components is more, most people think that hemorrhoids, epistaxis and menstruation all indicate that blood is harmful. Hippocrates believed that the change of seasons would lead to excessive blood, which would do harm to the body. People with excessive blood are called sanguine. Bloody people are prone to heart disease, epilepsy or leprosy, which can be treated with bloodletting and cold medicine. Hippocrates also noticed the anemia of pregnant women, and he thought that it might be because the embryo needed blood that caused the mother's anemia.

In the four-body fluid theory, another body fluid related to blood is "black bile". Because people can't see black bile under normal circumstances, it mainly appears in patients, so it is considered as the opposite of blood. Blood is generally considered beneficial, while black bile is harmful, such as black stool in patients with gastric ulcer bleeding, black vomiting in patients with gastric cancer, and "black urine disease" in patients with malignant malaria. These black (dark red) liquids that may be seen during illness become black bile. Because black bile can be seen in different situations, it may be a blood clot, or it may be a black blood sample substance when gastric ulcer vomits, so doctors think it is potentially destructive.

In ancient Rome, people had a better understanding of blood. Pliny Sr believes that the bone marrow "is red for young people and pale for old people." Rufus of Ives was a doctor during the reign of Emperor Trajan. He realized that jaundice was caused by blood changes after people were bitten by poisonous snakes.

Galen, the most famous doctor in ancient Rome, agreed with Hippocrates' theory of body fluids. He regards the function of body fluid as the basis of all kinds of temperament: those who are warm-blooded take dampness and temperature as their basic attributes and are controlled by blood; In a calm person, it is wet and cold mucus that controls the soul characteristics of the human body; Melancholy people are affected by dry and cold black bile; Irritable people are affected by dry and hot yellow bile. Galen's body fluid theory can explain human health, diseases and any related problems, and provide various possible answers for the therapeutic consequences of diseases.