The tenth century Chan master Yunmen said: "Medicine and sickness subdue each other—they mutually correspond. The whole earth is medicine. What is the self?"

Medicine and sickness, or poison and remedy, subdue each other; they correspond. Yunmen might have been defining the Greek word pharmakon, drug, meaning either poison or remedy, depending on context, or a spell, enchantment. Pharmacology is its child. And pharmakos, the scapegoat, hidden away in prison or hanging from the Cross, is its cousin.

Perhaps there was a wedding—poison and remedy—where friends of bride and groom didn't know on which side to sit. Elder married couples—such as samsara and nirvana, and form and emptiness—sat in the balcony. Someone threw rice.

Poisons are three or five, depending on lineage. As three, they are greed, hatred, and ignorance. On the bhavacakra, the Wheel of Life, the three poisons form the hub: the cock, the snake, and the black hog chasing each other and spinning the cycle of existence like a trimorphic ouroboros. As five, the Vajrayana tradition adds pride and jealousy, or envy, to the poisons. As ten, the poisons are kleśa, the ten defilements that spoil the immaculate purity of the ālaya-vijñāna, the "storehouse-consciousness". They are like graffiti, or pharmaka: polychromatic pigments, or makeup, applied to the world through discrimination and artistry. Or maybe we have the Seven Deadly Sins, the fly in the ointment whose name is Beelzebub. Either way, we are up to our nostrils. Or are we?

Which side are you on? Bride or groom? Some say not choosing is to side with the oppressors. Hands rise toward you in supplication. The hands are poisoned. Have been poisoned. Polluted, and sick. Self-poisoned. Hands with broken fingers. Dürer's hands. Hands at gasho. Give me alms. Give me medicine. If poison and remedy mutually correspond, there is no doctor and no patient, so whose hands could they be?

Song Dynasty master Shiqi Xinyue said: "The intent of our teaching is like a poison-smeared drum. Once it is beaten, those who hear it, near and far, all perish. That those who hear it perish is surely true. But what about the deaf?"

The whole earth is medicine. Somewhere a mockingbird sings. Clouds gather. A rain may fall. Shiqi beats his drum and the sky cracks with thunder. The raised hands have become an army, swaying back and forth like tall grass in a light breeze. What will you do?

If the whole earth is medicine, that must include both ayahuasca and the leaf of an oak tree. This leaf is bitter, as is the ayahuasca: the curling margins host a few spines. Maybe it is Zhaozhou's oak tree, in the garden or in the courtyard—the reason Bodhidharma came from the west. Surely this must be a medicine. But what medicine are you seeking? In matters of medicine, the oak leaf competes with the ayahuasca. Or perhaps that is backward. How is one to walk such a path, strewn with bitter brews and prickly oak leaves? Which are the sharper thorns?

Poison and remedy mutually correspond. The whole earth is remedy. What is the self?

This is the nub of the problem, the essential question for either approach—all else is distraction. Distraction is the poison, the disease. The "world" is distraction, yet the world is the medicine. From such a condition, Yunmen demands that we step forth and answer.