Since ancient times, people's life activities have always been closely related to the changes in nature, which is the foundation of life, and this is the yin and yang of heaven. Between heaven and earth, whether it is the land of nine continents in the world or the nine orifices, five internal organs and twelve knots of human beings, they are all connected with the natural qi. The yin and yang of heaven are the five elements of the birthplace, and Yin and Yang Qi are divided into three Yin San Yang according to their ups and downs. If a person often violates the changing law of yin and yang and five elements, evil spirits will do harm to human body. Therefore, adapting to this law is fundamental to the continuation of life.

When the weather between heaven and earth is clean, people's spirit will be adjusted accordingly and the yang will be enriched. Even if there is a thief's wind, evil spirits can't invade the human body. This is the result of adapting to the changes of Yin and Yang in time sequence, so saints can concentrate on breathing the essence of heaven and earth to understand the changes of Yin and Yang. If they violate this principle, they will be ignorant inside, will make their muscles stagnate outside, and their true qi will be dispersed rather than persisted. If the yang spirit loses its normal position and cannot play its important role, people will lose their life or die. If people feel cold evil, the yang will move in the body like the door shaft running in the door mortar. People will be restless in their daily lives, disturbing the yang spirit and making it leak and float. If they feel the evil of summer, they will be more harmful and irritable. Even if they stop breathing, they will talk a lot and have a high fever. Like charcoal fire, they must sweat and get hot. If you feel damp evil, your head will be as heavy as something. If damp-heat can't be eliminated in time, it will hurt the muscles and bones, the big muscles will contract but not stretch, the small muscles will be soft and weak, and the limbs will ache alternately. This is Yang's failure.

When the human body is excessively troubled, the yang will prevail and spread. Repeatedly, the yang will be more abundant, while the yin essence will decline. When it is hot every day in summer, it is easy to cause people to faint. The main symptoms are dim eyes, blind ears and deaf ears. When the human body is angry, the yang will fluctuate up and down, and blood will accumulate on the body with the rise of qi, which will be separated from other parts of the body.

If the opening and closing adjustment of sweat pores is abnormal, the cold will invade and damage the yang, causing the body to bend and not stretch. If the cold goes deep into the meridians, ying qi cannot run along the meridians. Obstruction between muscles, long-term and deep into blood vessels will lead to the formation of fistula sores.