I keep hearing about how, in regards to certain types of snake and spider, “a single drop of its venom can kill scores of people.” But I’ve always wondered how scientists arrived at this measurement. It certainly can’t come from actual tests – ethics aside, it would be a logistical nightmare to divide up a single drop of venom amongst dozens of people, even with today’s technology. But it also doesn’t sound like the sort of thing that’s been made up to scare people into avoiding the venomous creature, because just saying that you would die a slow, agonising death if you got bitten would be enough to scare people off. So how do they get this measurement?
In: Biology
The measurement is based off what’s called as an [median lethal dose](https://en.wikipedia.org/wiki/Median_lethal_dose) (LD50). Basically, it’s the dose (usually milligrams per kilogram body mass, mg/kg) at which half of the subjects die from exposure. They take a number of rats (or other animals) and administer a specific dose. Once that dose kills of 50% of the test population, the LD50 can be determined.
That number can be extrapolated to calculate how many people it can theoretically kill. For example, sodium cyanide has an LD50 of 6.4 mg/kg. This means 6.4 * 70 = 440 mg will have a 50% chance of killing 70kg person. If you have 4.4 grams of the substance, you can kill 50% of 10 people, ~5 people.
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