"The *Inner Canon of the Yellow Emperor* says, 'In spring and summer, nourish the yang.' And the renowned Qing Dynasty physician Zhang Lu recorded in his *Zhang's Medical Compendium*: 'During the Sanfu period in summer, applying white mustard seed paste is often effective.' This is the origin of the Sanfu patch."
"This method can unblock the meridians, warm the yang, and dispel cold. It's most effective for chronic problems like yours—cold pain in the joints and an aversion to cold. It serves to prevent illness before it starts and prevent existing conditions from worsening."
Wang Baimu listened, completely baffled. Although he didn't quite understand the concepts of yin, yang, and the five elements, he did grasp the principle of "using the sun's fire to expel the cold."
"Doctor Li, where can I buy these 'Sanfu patches'?"
Wang Baimu asked eagerly. "Are they expensive? I want to get some for everyone in the village."
