How Venom Flows
In some snakes the fang delivers deadly venom in much the same way that a hypodermic needle delivers medicine -- by rapid injection of a pressurized mass of fluid. But there is a second means of envenomation that is more common, and, perhaps, also biophysically more elegant. In the majority of venomous snakes and in all other venomous reptiles, the venom is not released under pressure, but rather seeps from the venom gland along an open groove. Nevertheless, to be effective against other organisms, the venom has to penetrate through the superficial layer of skin and infiltrate the deeper tissue. How does venom infiltrate in the absence of pressure? By using a combination of analytical techniques, experiments, and biophysical modeling, a team of researchers has solved the above paradox. Two key findings have emerged. First, the surface tension acting on the venom is the dominant physical force underlying envenomation; it literally shapes the flow of the venom, and ensures that it sticks when necessary while waiting for prey whereas any break in the prey's skin will act as a venom attractant and suck the venom into the deeper tissues. Second, the influence of surface tension is enhanced by the presence of open grooves on the surface of the tooth or fang. A grooved fang is common among living and extinct reptiles. The contours of the groove enable the venom to conform and flow in such a way that, as a consequence of surface tension, it minimizes the surface energy. In this way it can also be understood how during evolution the groove contour might well adapt to the nature of the prey's skin cover, such as feathers.
