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When going through this link, Table 1, what are the numbers mentioned there? How is one quantifying toxicity?

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Usually, toxicity is given in the units of mass of the substance per unit mass of body mass of the organism that will kill 50% of the organisms in a species if those organisms ingest the toxin at that dose (e.g. mg/kg, ng/kg). This measurement is called the median lethal dose, and is often abbreviated as LD50.

In your table, they only provide the mass of the (average) dose of the substance needed to kill the organism listed, as can be seen by the (mg) after the words "Toxic dose". They likely multiplied the LD50 of the toxin by the average mass of the organism to obtain those numbers. Based on Google's estimation that a mouse has an average weight of 0.68 oz (0.019 kg), and on this table of murine LD50 measurements, I calculated that for tetanus toxin, the lethal dose in the average mouse is 3.8x10$^{-8}$ mg, which is basically what your table provides, which supports my guess on how they obtained their numbers.

The other values listed under "Lethal toxicity compared with" appear to be ratios, given by the formula [lethal dose of toxin above]/[lethal dose of toxin on left]. Using Wikipedia's LD50 for Strychnine in mice (2 mg/kg) and the tetanus toxin LD50 from my previous source, I obtain the exact ratio that they do (1x10$^6$). The lack of units makes sense, as ratios are unitless.

Source on LD50

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    $\begingroup$ "needed to kill 50% of the organisms of a species tested", what does this mean? $\endgroup$
    – girl101
    Commented Jun 8, 2016 at 5:55
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    $\begingroup$ It means that when they were testing the drug on animals, 50% of the animals tested died when given the dose. So, if the LD50 of X is 1 mg/kg in mice when ingested orally, then 50% of mice can be expected to die if they consume 1 mg of X orally for every 1 kg of their own mass. $\endgroup$
    – TreeHouse196
    Commented Jun 8, 2016 at 5:57
  • $\begingroup$ no my question is whichever value is the correct value, how can one get that correct value. How is the quantity of the toxin related to the functionality of the host? $\endgroup$
    – girl101
    Commented Jun 9, 2016 at 4:49
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    $\begingroup$ @Rishika I am not sure I quite understand your question. If you want to know how LD50 is calculated, the LD50 value is obtained experimentally. If you want to familiarize yourself with the methods used to calculate LD50 values, I would read some articles that report research doing that. Here is an article I found with a quick pubmed search where the LD50 of several compounds was calculated in silkworms: jstage.jst.go.jp/article/ddt/10/1/10_2016.01025/_pdf. If this does not answer your question, I would encourage you to post it as a new question on stack exchange. $\endgroup$
    – TreeHouse196
    Commented Jun 9, 2016 at 5:27
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    $\begingroup$ A small note: There are some other measures too such as Maximum Tolerated Dose, Minimum Lethal Dose, therapeutic index etc. $\endgroup$
    – WYSIWYG
    Commented Jun 9, 2016 at 8:52

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