Hemlock (Conium maculatum) is a common plant, and is considered dangerous.
One of the biggest dangers is that it is occasionally mistaken for edible root vegetables, despite the distinctive spotty stems. ( maculatum means “spotty”).
The extracted oil is called Coniine, and apparently smells of mouse urine.
I was once told , while working in the Apothecary Hall, by a “learned man”, that hemlock would never have been used medicinally as it was poisonous. Surprisingly for me, I didn’t argue with him.
However, it most definitely WAS used for a number of conditions, including as a sedative, anti spasmodic, breathing conditions such as asthma and bronchitis, and as an ointment for piles.
It went out of favour because there is a very narrow margin between a safe dose and a lethal dose. By 1934, it was no longer recommended in the British Pharmaceutical books. Its use had been largely discontinued by ships surgeons probably a couple of hundred years before this, because the medicinal parts of the plant material deteriorate fairly quickly.
Hemlock was used to kill criminals, the most famous being Socrates, who self administered the fatal drink.
He was fully conscious until shortly before the end, as his body slowly shut down, and I would imagine that the last couple of minutes were silent hell as he suffocated due to his lungs ceasing operation.
One of the stories regarding the poisoning effect of hemlock refers to the Israelites in the desert, who tiring of their diet of Manna, captured and ate a large number of quail, then fairly quickly died.
For over two thousand years, people believed that the flesh of the birds had become poisonous because they eat hemlock seeds during their migration; they are impervious to the hemlock, but it makes their flesh poisonous. However some recent research suggests that this may not be true. Quail actually shun hemlock, and when they were fed it they died! It now seems extremely probable that the offending poisonous plant might be Hellebore! (cyanide compounds are also being considered, as birds seem to have a high tolerance to Hydrogen cyanide)