Hemlock is a neurotoxin which paralyses the nervous system. Hemlock is the name of the plant from which the poison comes, the active component is coniine, an alkaloid. It acts from the extremities and moves up the body until it reaches the torso, at which point breathing is arrested. The Greeks wrongly believed that death was due to the poison stopping the heart. In fact the victim asphyxiates.
Hemlock was the poison of choice for offing citizens of Athens, so long as their crime wasn't bad enough to merit something nastier, such as stoning. Hemlock was very much the easy option, and of course its most famous victim was Socrates. There are actually a number of plants in the hemlock family. The one used to make the poison which executed Socrates was
Conium maculatum, called simply Poison Hemlock. There's also Water Hemlock, which if anything is even more toxic, and a tree called hemlock.
Two things I better say right at the start, just in case some idiot eats hemlock and survives to sue me: don't even think about touching the stuff; also, I'm not a doctor.
Every part of the plant is toxic, but the roots and berries particularly so.
Believe it or not, some Greek doctors prescribed hemlock as a medicine. In fact hemlock was used as a herbal medicine up until relatively recent times. Clearly doctors' professional practice insurance isn't what it used to be. For what did they prescribe it? Arthritis, and any disease that involved involuntary movement. The paralytic effect stopped the shaking.
The danger is that the difference between a medicinal and a fatal dose is very, very small. I've read texts which suggest 1 leaf is medicinal and 6 leaves is fatal. But of course your mileage will vary depending on the individual plant, which parts were used, and the size and sensitivity of the patient-cum-victim.
There have been well documented cases of accidental poisoning in the last hundred or so years, some of them very tragic. I've read of one case where someone sucked a tuber of water hemlock, having mistaken it for a different, edible plant. Poison hemlock resembles parsley closely enough that someone could make a mistake. Children playing in the woods are particularly vulnerable, both because they're more likely to make the mistake and because with their smaller bodies the poison takes effect quicker.
The effect of hemlock seems to vary widely. Some cases record convulsions, others report the victim dying quietly over hours and remaining conscious and rational to the end, which was the experience of Socrates.
There's no cure, but if you do accidentally ingest hemlock and you realize it in time, then all is not lost. It takes quite a while to die, and if you can get to a hospital in time -- don't run, in fact don't move at all if you can help it -- then they'll put you on an artificial breathing and heart pump machine until the paralysis has worn off, after which you should be okay, if somewhat terrified.
Here's a picture of Poison Hemlock:
This gorgeous image belongs to
J. Alex Halderman, an amateur photographer of very great skill.
Hemlock is present as a weed in Australia. It was deliberately introduced by some moron who thought there weren't enough poisonous things in this country, so he added one more.
Here's the famous description of the death of Socrates. It was written by Plato in his book
Phaedo. I've taken it from the online Perseus edition.
Thereupon Crito nodded to the boy who was standing near. The boy went out and stayed a long time, then came back with the man who was to administer the poison, which he brought with him in a cup ready for use. And when Socrates saw him, he said: “Well, my good man, you know about these things; what must I do?” “Nothing,” he replied, “except drink the poison and walk about till your legs feel heavy; then lie down, and the poison will take effect of itself.”
...
He walked about and, when he said his legs were heavy, lay down on his back, for such was the advice of the attendant. The man who had administered the poison laid his hands on him and after a while examined his feet and legs, then pinched his foot hard and asked if he felt it. He said “No”; then after that, his thighs; and passing upwards in this way he showed us that he was growing cold and rigid. And again he touched him and said that when it reached his heart, he would be gone. The chill had now reached the region about the groin, and uncovering his face, which had been covered, he said—and these were his last words—“Crito, we owe a cock to Aesculapius. Pay it and do not neglect it.” “That,” said Crito, “shall be done; but see if you have anything else to say.” To this question he made no reply, but after a little while he moved; the attendant uncovered him; his eyes were fixed. And Crito when he saw it, closed his mouth and eyes.Some people have actually used this passage to suggest Socrates was not killed by hemlock. The major objection is that Socrates' legs are described as cold and rigid. It's got to be wrong. Hemlock produces a flaccid paralysis.
However in the past 100 years there have been some cases of accidental poisoning which precisely matched the symptoms Plato describes, except for the flaccid muscles. The obvious answer is Plato is being misread here (easy to do with one word after 2,500 years) or else it's a copy error.
Hemlock is said to have a fetid taste, somewhat akin to a mouse. It can't be all that strong though, considering the number of people who've eaten it accidentally. One man even ate it in a sandwich. Nevertheless any mouse odor is easily masked by mixing it with Ancient Greek wine, which often had fenugreek added. I personally have tasted a similar Roman wine called
Turriculae. Believe me, Turriculae could mask almost anything.
I suspect the execution potion that killed Socrates was hemlock mixed with strong wine.
Another possibility, clearly not used with Socrates since he remained rational, would be to add a sedative. Greek medicine was very primitive, but we know they were expert at making opium. It makes sense to mix poppy juice with the hemlock; not everyone would be as calm about dying as Socrates was, and it's easy to imagine a distraught prisoner causing considerable trouble. After a good slug of poppy juice the prisoner wouldn't care if his legs fell off, let alone lost feeling. This is the ancient world's equivalent of death by lethal injection, and I'm not sure it isn't just as effective and perhaps even more merciful.