The Divine Farmer's Materia Medica

Ancient people ate grasses and drank water. They gathered the fruit
from trees and ate the meat of clams. They frequently suffered from
disease and poisoning. Then Shen Nong taught people for the first
time how to sow the five grairs, to observe whether the land was
dry or wet, fertile or rocky, located in the hills or in the lowlands.
He tasted the flavors of all the herbs and springs, [determiningl whether they were bitter or sweet. Thus he taught people what to avoid and where they could go. At that time. [Shen Nong] encountered 70 [herbs] in one day, [determining which were] medicines and [which were] poisons.r