"The lung is connected with skin and hair" is a theory of traditional Chinese medicine. From the view of comparative physiology we researched the inter-relation of lung and skin and hair and found it in water. From living protein to fish respiration is by the structure corresponding to the skin and the organ which originated skin. Though amphibia have lung respiratory effect of skin still locate 2/3. Aves. Mammals and human beings use lungs to respire. In fact air exchanges from nature through the thin water molecular layer of the surface of the pulmonary alveoli. So the lung is derived from "skin and hair" to adapt to inter-respiration.