In addition, in order to resist the fallacy of "God-given disease", Hippocrates actively explored human characteristics and the causes of diseases, and put forward the famous "body fluid theory". The theory of four body fluids is not only a pathological theory, but also the earliest theory of temperament and physique. He believes that a complex human body is composed of four kinds of body fluids: blood, mucus, jaundice and black. Four kinds of body fluids account for different proportions in the human body, forming different temperament of people: impatience and agility; Blood with active temperament and sensitive movements; Quiet and slow-moving mucus; Depressed patients with fragile personality and slow action. Everyone, whose physiological characteristics are dominated by which liquid, corresponds to which temperament. The performance of innate personality will be adjusted with the change of acquired objective environment, and personality will also change accordingly, which provides a certain guiding basis for future medical psychotherapy. People get sick because of the imbalance of four fluids. Liquid imbalance is the result of external factors. Therefore, he believes that when doctors enter a city, they should first pay attention to the trend, soil, climate, wind direction, water source, water, eating habits and lifestyle of the city, which are closely related to people's health and diseases.

Now it seems that Hippocrates' explanation of the causes of human temperament is not correct, but the name and division of temperament types he put forward have been used to this day. At that time, religion and customs prohibited autopsies. Hippocrates bravely broke through the ban and secretly dissected the human body, gaining a lot of knowledge about the human body structure. In his most famous surgical work, Head Trauma, he described in detail the cases of head injury and dehiscence, and put forward the surgical methods. The record of the operation is very detailed and the language used is very accurate, which proves that this is a summary of his personal experience.

In his collection of essays, Proverbs, he compiled many wise sayings about medicine and life, such as "life is fast and skills are long"; "Opportunity is rare, experiment is risky, and decision-making is more valuable"; Overeating hurts the body: "Sleepiness for no reason is a precursor to illness"; "A simple and delicious diet is more beneficial than a fine but unpalatable diet"; "Hope in nature" and so on, these experiences are widely known and still inspire people today.