The author of the present paper holds that "Qi-passage" is in fact the essence of meridian-collateral system in the human body.In my opinion

the so called "Jing" of the fourteen meridians is referred to the tissue structure of the longitudinal fascia space;the so called "Luo" of the fifteen collaterals referred to the tissue structure of the transversal fascia space

and the "Mai" of meridians and collaterals referred to tissue liquid-Qi of both longitudinal and transversal fascia space.The "Dao"(Qi-passage) of meridians and collaterals is the tissue structure of both longitudinal and transversal fascia space.The tissue liquid-Qi and tissue structure depend on each other.The doctrine of "Qi-passage" of meridian-collateral system has its original evidence

scientific and substantive basis.The meridian-collateral system is a regulative and control system of the unknown synthetic functions of multiple substances including loose connective tissue

tissue liquid-Qi

energy substances

nerves

blood vessels and lymph

etc..