难经 · 论针法 · 七十五难

曰yuē：经jīng言yán，东dōng方fāng实shí，西xī方fāng虚xū；泻xiè南nán方fāng，补bǔ北běi方fāng，何hé谓wèi也yě？

然rán：金jīn、木mù、水shuǐ、火huǒ、土tǔ，当dāng更gēng相xiāng平píng。东dōng方fāng木mù也yě，西xī方fāng金jīn也yě。木mù欲yù实shí，金jīn当dāng平píng之zhī；火huǒ欲yù实shí，水shuǐ当dāng平píng之zhī；土tǔ欲yù实shí，木mù当dāng平píng之zhī；金jīn欲yù实shí，火huǒ当dāng平píng之zhī；水shuǐ欲yù实shí，土tǔ当dāng平píng之zhī。东dōng方fāng肝gān也yě，则zé知zhī肝gān实shí；西xī方fāng肺fèi也yě，则zé知zhī肺fèi虚xū。泻xiè南nán方fāng火huǒ，补bǔ北běi方fāng水shuǐ。南nán方fāng火huǒ，火huǒ者zhě，木mù之zhī子zǐ也yě；北běi方fāng水shuǐ，水shuǐ者zhě，木mù之zhī母mǔ也yě。水shuǐ胜shèng火huǒ。子zǐ能néng令líng母mǔ实shí，母mǔ能néng令líng子zǐ虚xū，故gù泻xiè火huǒ补bǔ水shuǐ，欲yù令líng金jīn不bù得dé平píng木mù也yě。经jīng曰yuē：不bù能néng治zhì其qí虚xū，何hé问wèn其qí余yú，此cǐ之zhī谓wèi也yě。