Yin-Yang
The meaning of Yin-Yang:
This Simbol(Yin-Yang) represents the ancient Chinese understanding of how things work. The outer circle represents "everything", while the black and white shapes within the circle represent the interaction of two energies, called "yin" (black) and "yang" (white), which cause everything to happen. They are not completely black or white, just as things in life are not completely black or white, and they cannot exist without each other.
While "yin" would be dark, passive, downward, cold, contracting, and weak, "yang" would be bright, active, upward, hot, expanding, and strong. The shape of the yin and yang sections of the symbol, actually gives you a sense of the continual movement of these two energies, yin to yang and yang to yin, causing everything to happen: just as things expand and contract, and temperature changes from hot to cold.
Yin and Yang In Medical Theory:
The concepts of Yin and Yang and the Five Agents provided the intellectual framework of much of Chinese scientific thinking especially in fields like biology and medicine The organs of the body were seen to be interrelated in the same sorts of ways as other natural phenomena, and best understood by looking for correlations and correspondences. Illness was seen as a disturbance in the balance of Yin and Yang or the Five Agents caused by emotions, heat or cold, or other influences. Therapy thus depended on accurate diagnosis of the source of the imbalance.
Cooling, yin symptom might be treated with hot meals, which are yang, a nervous breakdown, yang, would be treated with cold foods (like fruit), which are yin. Also when trying excess yin or yang, always take into account the possibility of the existence of a deficiency the opposite pole. If yin deficient, it can tone the yin to that, once reinforced exert its inhibitory action on the yang.
The earliest surviving medical texts are fragments of manuscript from early Han tombs. Besides general theory, these texts cover drugs, gymnastics, minor surgery, and magic spells. The text which was to become the main source of medical theory also apparently dates from the Han. It is the Yellow Emperor's Classic of Medicine, supposed to have been written during the third millennium BCE by the mythical Yellow Emperor.