A bit of arithmetic on the amount of venom in a fang:

- According to the diagram of a rattlesnake fang longitudinal section in Klauber's epic volume, the diameter of the venom canal in a fang is about 1/20th the length of the fang.

- Let's assume a puff adder fang with a venom canal 1 mm across and 20 mm long (generous, to be sure). The volume of the venom canal would be the radius squared times pi times the length of the fang, or 0.25 * 3.14 * 20 = 15.7 cubic millimetres - call it 16 - that is to say 16 microlitres. If this entire volume of the fang canal was full of liquid venom when the fang was shed (and obviously lost externally, not digested), then the 16 microlitres of venom would weigh approx 16 milligrams. In general, approx. 1/4 of the wet weight of the venom is solids, i.e., the 16 milligrams of wet venom would dry into 4 milligrams of dry venom, i.e., a very small fraction of the usual venom yield of 100-200 mg.

- Taking it further, how much of these 4 mg would be absorbed into tissues from a fang that is accidentally poked into the skin? Anyone who has ever had to wash dried-on spitting cobra venom off their goggles or camera lens knows that venom, once dried, is not that easily or quickly dissolved. Moreover, if the entire venom canal was full of dried venom, the inner parts, away from the two orifices, would be out of reach of the tissue fluids that might dissolve it. So, my guess is that less than half of the venom that might possibly be in the fang would ever get into the wound, or in this example 2 mg - compared to a lethal dose of 50-100 mg.

Given that 8 vials of SAIMR antivenom for puff adder bites (likely to have injected at least 10s if not 100s of mg of venom) would be considered a large dose, this simply does not compute. Either the patient had some sensitivity reaction (does that make sense from the symptoms?) and the antivenom was given in error, or we are missing something else here.

There have been documented cases of serious envenomation from puncture wounds from dried Australian elapid skulls, to the concept as a whole is not absurd, but thisparticular case raises more questions than it can answer.

John, regarding your rear-fang question: All colubroid snakes have some movement in their maxillae. Some rear-fangs, like Waglerophis and Xenodon as wel as boomslangs, have a lot more than others.

Regarding the evolution of rear-fangs, chances are that the earliest colubroids may already have had grooved rear fangs. However, the character is highly evolutionarily labile, and grooved fangs have been lost and gained multiple times int he "Colubridae", so it is hard to trace any particular feature back with any degree of certainty.

Cheers,

Wolfgang
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