The Doctrine of Signatures

People are very good at recognizing patterns, even where no pattern exists, and pattern recognition played an important part in early herbal medicine. When people rummaged through the meadows and along the hedgerows for plants that might heal their ailments, they saw similarities between plant forms and the part of the body that was sick. In time the existence of these similarities acquired a theological justification.

In the 16th century, the Swiss physician, alchemist, and astrologer Paracelsus (1493–1541) challenged many of the accepted medical views of his day. He called himself Paracelsus—beyond Celsus—to show his superiority to the Roman encyclopedist Aulus Cornelius Celsus (ca. 25 b.c.e.–ca. 50 c.e.), whose book De medicina (About medicine) summarized Roman medical knowledge. Paracelsus's real name was Phillip von Hohenheim and he also called himself Philippus Theophrastus Aureolus Bombastus von Hohenheim. He spent much of his life traveling as a vagabond with a group of supporters, but eventually he settled down as professor of medicine at the University of Basel, where he dramatically burned several of the existing textbooks. Paracelsus attacked the greed of apothecaries and quarrelled with the medical establishment. He believed that diseases were caused by external factors rather than imbalances within the body, and he aimed to discover a cure for every complaint. He was a very successful doctor, but highly unpopular with the authorities.

Paracelsus also maintained that God had left clues hinting at the true purpose of all the objects he had created and that the skill of the physician depended on understanding the divine clues relating to the treatment of disease. For example, Paracelsus taught that pricking the patient with a thistle was an effective treatment for internal inflammation. He pointed out that the seeds of skullcap (Scutellaria species) resembled skulls—hence the name—and that the plant cured headache. Willow (Salix species) grows in damp places and cures rheumatism, which is associated with dampness. It was not a new idea, and the uses of plants were often reflected in their names. For example, snakeroot (Ageratina species) was supposed to be an antidote to snake venom, toothwort (Lathraea species) to relieve toothache, and liverwort (Hepatica species) to cure liver disorders. The illustration above shows the features of toothwort and lungwort on which the similarities were based.

Left: Toothwort (Lathraea squamaria) leaves have edges suggestive of a row of teeth. Right: The blotches on lungwort leaves (Pulmonaria officinalis) are reminiscent of the surface of lung tissue.

This is the teaching that came to be known as the doctrine of signatures, the signatures being the marks God had used to label plants. The German theologian and mystic Jakob Bohme (1575–1624) developed and popularized the doctrine in his book Signatura rerum (The signature of all things), published in 1622, and in the years that followed the supposed links grew. People believed that long-lived plants promoted longevity, plants with yellow sap cured jaundice, eyebright (Euphrasia species) was good for eye ailments, lousewort (Pedicularis species) repelled lice, and there were many more. The English herbalist William Coles (1626–62) mentioned in his book The Art of Simpling, published in 1656, that walnuts “bear the whole signature of the head,” and wrote of viper's bugloss (Echium vulgare) that “its stalks all to be speckled like a snake or viper, and is a most singular remedy against poison and the sting of scorpions.” Nicholas Culpeper also promoted the doctrine.

These beliefs were not confined to Europe. People in most cultures have associated the colors, shapes, and markings of plants with parts of the human body. Obviously there can be no true links of this kind and supposed similarities between plants and organs of the body are purely coincidental. The doctrine of signatures is pure superstition with no rational basis.