Qi “If one has the ability to know the seven injuries and the eight advantages, one can bring the two principles into harmony. If one does not know how to use this knowledge, his life will be doomed to early decay. By the age of forty, the Yin force in the body has been reduced to one-half of its natural vigor, and an individual’s youthful prowess has deteriorated. By the age of fifty, the body has grown heavy. The ears no longer hear well. The eyes no longer see clearly. By the age of sixty, the life-producing power of Yin has declined to a very low level. Impotence sets in. The nine orifices no longer benefit each other. “Those who seek wisdom beyond the natural limits will retain good hearing and clear vision. Their bodies will remain light and strong. Although they grow old in years, they will stay able-bodied and vigorous and be capable of governing to great advantage. For this reason the ancient sages did not rush into the affairs of the world. In their pleasures and joys they were dignified and tranquil. They did what they thought best and did not bend their will or ambition to the achievement of empty ends. Thus their allotted span of life was without limit, like that of heaven and earth. This is the way the ancient sages controlled and conducted themselves. “By observing myself I learn about others, and their diseases become apparent to me. By observing the external symptoms, I gather knowledge about the internal diseases. One should watch for things out of the ordinary. One should observe minute and trifling things and treat them as if they were big and important. When they are treated, the danger they pose will be dissipated. Experts in examining patients judge their general appearance; they feel their pulse and determine whether it is Yin or Yang that causes the disease. To determine whether Yin or Yang predominates, one must be able to distinguish a light pulse of low tension from a hard, pounding one. With a disease of Yang, Yin predominates. With a disease of Yin, Yang predominates. When one is filled with vigor and strength, Yin and Yang are in proper harmony.”