《梦溪笔谈·药议》
人的饮食及服用的药饵既入肠胃，为人体的精气所蒸化，其精华部分以至金石之物的精华成分一一如经过精细加工的硫黄、朱砂、钟乳石之类一一凡是能够流动融合的，都随着精气畅达肌骨，犹如天地间的精气贯通金、石、土木等万物，从未有滞留和阻碍；其余的不能被精气所蒸化的部分，譬之顽石、草、木，则只是某些气味随着精气畅达各处，及其气味的功能也用尽，就变成渣滓和秽物传入大肠，又润湿渗透于小肠，这些都是废物，不能再转变消化，只能被排泄出去。
凡人饮食及服药既入肠，为真气所蒸，英精之气味，以至金石之精者，如细妍硫黄、朱砂、乳石之类，凡能飞走融结者，皆随真气洞达肌骨，犹如天地之气，贯穿金石土木，曾无留碍。自馀顽石草木，则但气味洞达耳。及其势尽，则滓秽传入大肠，润湿渗入小肠，此皆败物，不復能变化，惟当退洩耳。
After human food and medicinal bait enter the intestines and stomach, they are vaporized by the essence and qi of the human body, and their essence, as well as the refined essence of gold and stone, such as refined sulphur, cinnabar, and stalactite. All things that can flow and blend can reach the muscles and bones along with the essence and qi, just like the essence and qi of heaven and earth penetrate all things such as gold, stone, earth, and wood, and never remain stagnant or hinder; the rest that cannot be vaporized by the essence and qi, such as stubborn stone, grass, and wood, only some of the smell can reach everywhere with the essence and qi, and when the function of the smell is exhausted, it will become dregs and filth and enter the large intestine, and moisten and penetrate the small intestine, these are waste products that can no longer be digested, they can only be excreted.