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In 1136, Hildegard of Bingen was elected as mother superior of her Benedictine convent in Germany. Although best known today as a composer of sacred music, Hildegard was a polymath who wrote extensively on theology, philosophy and science. She composed *Physica*. It is considered one of the first books of scientific natural history produced in Germany.
Hildegard's encyclopaedic work documented the healing properties of the natural world. Unlike her mystical writings, *Physica* was grounded in her practical experience tending the monastery's infirmary and physic garden. She believed human health was deeply tied to the environment, a connection she explained through the framework of medieval humorism.
What did Physica cover?
*Physica* catalogued the natural world across nine books. She described the scientific and medicinal properties of various:
Plants
Stones
Fish
Reptiles
Animals
Her classifications relied on the concept of *viriditas*, or "greening power" — a vital life force she believed sustained the health of both plants and human beings.
How did humoral theory explain medicine?
To prescribe treatments, Hildegard used the classical theory of humorism, which linked human health to the balance of four bodily fluids: blood, yellow bile, black bile and phlegm. These humors corresponded to the four elements (air, fire, earth and water) and their pairs of physical qualities (hot, cold, moist and dry).
If a patient fell ill, a physician deduced which humor was in excess. A fever, for example, indicated an excess of heat and dryness (yellow bile), which would be treated with herbs categorised as cold and moist. Hildegard carefully assigned these inherent qualities to the plants and stones she described.
How did she use plants in medicine?
Hildegard used a vast array of flora to counteract illnesses. Her remedies were grounded in practical observation.
For example, *Physica* is thought to contain the first recorded reference of the use of hops in beer as a preservative. Hildegard noticed that adding hops prevented the drink from spoiling.
How do we read historical scientific texts?
When we read early natural history like *Physica*, we see a mix of what we now call science and prescientific philosophy. A useful framework for studying historical texts is to separate the observation from the explanation:
Look for empirical observation: Hildegard noticed that adding hops to beer prevented the drink from spoiling over time. This was a true, repeatable physical observation.
Identify the underlying theory: Scholars of the period interpreted their findings through humoral qualities, assigning elemental properties to the plants and minerals they tested.
Compare with modern evidence: Today, we know the preservative effect of hops comes from antibacterial compounds, rather than an elemental subtlety.
If you are exploring how historical classifications evolved into modern biology, the Fermi Concept Library has every concept in physics, chemistry, biology, mathematics and computing, each with its own lesson and its place in the map, showing where ancient ideas meet modern evidence. The transition from humoral theory to cell theory and microbiology is a core part of understanding how scientific reasoning builds upon — and corrects — the observations of the past.
For more on how early scientists catalogued nature and its substances, see Li Shizhen and the great compendium of medicinal substances and Alexander Oparin and the primordial soup theory of life.
