Guest Post by Laura Cooper
For much of human history, people have sought to find a way to prove or disprove a person’s guilt. Today, we hope evidence and a fair trial will do this, but people have always wanted a quick and definitive way of doing this. This is where the idea of the trial by ordeal came in. Most people are familiar with the practice of dunking suspected witches in bodies of water in parts of 17th century Europe; if they floated they were guilty and if they sunk they were innocent. But in what was then called the Calabar region (now North-East Nigeria) in the 19th century, a particularly poisonous seed was used in these trials by ordeal. This plant, known as the Calabar bean, Physostigma venenosum, became notorious as a poison. However, the principle lethal chemical of the Calabar bean, phystostigmine, was investigated by a number of physicians in Europe as an antidote to poisoning by atropine. Though both compounds can kill, their methods of murder are mirror images of each other, so that one can be used to cancel out the effects of the other; and so a poison can become a cure.
I can only find reports of the use of P. venenosum in ordeals in reports by Europeans visiting Calabar in 1846, who reported that 120 people died annually in the region by the Calabar bean. A person suspected of a misdeed would be made to consume the bean, likely soaked and crushed to release the toxins rather than whole. If they were guilty they would die, if they were innocent they would survive. It has been reported that swallowing the bean probably won’t result in death, but consuming a crushed seed would release toxins, like Abrus precatorius. Consuming enough seeds can lead to increased salivation, seizures, loss of control of urination and defectation and death by asphyxiation. Physostigmine has an oral LD50 (a dose which will kill half of a large group of mice) of 4.5 mg/kg, and the maximum number of beans reported eaten and survived is 35. Depending on a person’s weight and health, it is possible that one person may survive and another die after being given the same number of beans, and this difference can be attributed to their guilt or innocence.
The bean extract was known by medics in Europe, and extracts were used to constrict the pupil by ophthalmologists. Aware of it’s effects, in 1864 the Prague ophthalmologist Niemetschek suggested that a patient with atropine poisioning be given Calabar bean. Thomas Fraser investigated the effects of P. venenosum extract rigorously, and identified the chemical phystostigmine as the active chemical.
Phystostigmine acts as an acetylcholinesterase inhibitor. This means it prevents the neurotransmitter acetylcholine from being broken down, so the parasympathetic nervous system is continually stimulated. This is the exact opposite effects of atropine, an anticholinergic drug derived from Atropa belladonna, which I have written about before. Atropine causes anticholinergic syndrome, making the patient “dry as a bone, blind as a bat, red as a beet, mad as a hatter, hot as a hare”, as medical students remember it.
But many other chemicals and conditions can cause anticholinergic syndrome, and despite many published cases of phystostigmine being used to treat anticholinergic syndrome safely and effectively, it has been reported as being underused. It could be speculated that this underuse could be due to the gruesome reputation of the source of the chemical, the Calabar bean, and therefore a hesitancy to recommend the drug. But whilst the drug is dangerous at a high enough dose, the ordeals themselves show that it is survivable (if you are innocent, that is!). We return again to the common theme of plant poisons; everything has a lethal dose, even water, what is more interesting is what doses lower than this can do to the human body.