I read the article linked by Joel. Pretty interesting, and I think I agree about what it says about the Greek: ψύχοιτό doesn’t need to mean literally “grew cold” (as e.g. in inadequate blood supply), and πήγνυτο doesn’t need to mean “grew stiff” (as opposed to flaccid; stiff paralysis implies a problem of the central nervous system); I think both verbs could just mean that Socrates had increasing difficulties in moving his limbs.
But there are some problems with the article that are not negligible.
Did Socrates have sensory symptoms along with motor ones? The motor weakness caused by the poison provoked a failure of the respiratory muscles, and that would have been the cause of death. What I was able to find on poison hemlock is consistent with this, and this is also what the article is saying. According to what I understand, poison hemlock affects acethylcholine receptors both in the central nervous system and (what’s more relevant here) peripherally in neuromuscular junctions, which it blocks – i.e. it prevents the order to contract from passing from the nerve to the muscle. Poison hemlock poisoning simply does not cause a peripheral (poly)neuropathy, as far as I can understand. The article is simply mistaken about that. Poison hemlock should not have any effect on sensory transmission, which is unaffected when neuromuscular junctions are blocked.
Socrates says that he couldn’t feel his feet (σφόδρα πιέσας αὐτοῦ τὸν πόδα ἤρετο εἰ αἰσθάνοιτο, ὁ δ’ οὐκ ἔφη). I wouldn’t make too much out of this, though. Nowadays people generally know a lot more about physiology than then, but I can tell from experience that they are often surprisingly inept at telling about this sort of symptoms. For example, they confuse sensory with motor symptoms (weakness vs. loss of sensation/tingling etc.) and even with vascular ones. If, say, their hand is numb because of a nerve problem, they might say that blood isn’t circulating properly, or that the hand is swollen; I’ve even heard someone say that the hand is cold, when it most certainly was not. Or if the problem is demonstrably only motor without sensory deficit, they still might complain that the hand is numb. The article doesn’t take account of what seemed to be Socrates’ sensory symptoms, though I don’t think this deficit is really crucial. Anyway, I’d suppose that once Socrates was in his death throes, he could have had this sort of sensations even if his sensory nerves were intact.
However, bringing Guillain-Barré syndrome (GBS) at all into this was very infelicitous and confusing, for several reasons.
First, GBS isn’t a problem of neuromuscular junctions, it’s a problem of nerves. More exactly, it’s an acute polyneuropathy, most typically an acute demyelinating neuropathy, which means that the myelin sheaths that enwrap the nerves are damaged and nerves stop working properly (myelin basically provides electrical insulation to the nerves so that they conduct impulses better and faster). GBS affects both sensory and motor nerves. Also, the onset of GBS typically takes from a few days to a couple of weeks, not minutes or hours like in Socrates’ case, and GBS is often painful. So, both GBS and poison hemlock poisoning are “ascending”, and both might cause death by respiratory failure because of muscular weakness, but that’s about where the analogy ends.
If an analogy between poison hemlock poisoning and another disorder were really needed, myasthenia gravis would have been much better, as it affects specifically the neuromuscular junction (dropping of the eyelids, as described in Joel’s article as a symptom of Hemlock poisoning, is also a typical symptom of myasthenia).
So, forget anything the article says about Guillain-Barré syndrome, it’s utterly irrelevant to Socrates’ death. The 19th century descriptions of poison hemlock poisoning in the article were genuinely interesting, though.
What I was left wondering is that according to some other sources, poison hemlock poisoning should also cause all sort of other symptoms, like gastric problems, tachycardia, salivation etc. I wonder if these were unimportant enough to be left out of Plato’s description. Anyway, one problem with the identification is that poison hemlock poisoning seems to be excessively rare nowadays, so that we simply do not know enough.
EDIT: My post is terribly long and rambling, I’m afraid it’ll be difficult to understand unless you know a lot about pathologies of the peripheral nervous system. If anyone finds this interesting, ask and I’ll try to explain.
I corrected one mistake “ψύχοιτό doesn’t need to mean”.
EDIT2: “So, forget anything the article says about Guillain-Barré syndrome, it’s utterly irrelevant to Socrates’ death.”
Actually, it would be better to say that Guillain-Barré is irrelevant to poison hemlock poisoning.
To summarize: Guillain-Barré has both sensory and motor symptoms and is a nerve problem (neuropathy), hemlock poisoning has only motor symptoms and is a neuromuscular junction problem. The article is unaware of this difference. It is the presence of sensory symptoms that seems to me to be the biggest problem of identifying Socrates’ poison with poison hemlock, but see my post. (The symptoms as described by Plato do actually resemble Guillain-Barré syndrome, only with a much faster onset.)
What a rambling post this is!