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That Reminds Me…

That Reminds Me…


Our new minivan is equipped with airbags. They seem a little scary. The car manual recommends that young children not sit in the front passenger seat, that adults like me push the seat as far back as possible, that one not lean forward over the dashboard etc. etc. How tedious! Just what are these things that lurk in the front of our vehicle? Everyone knows they are a safety device. But just the same airbags seem like a monster which is difficult to control. It’s almost like having a tiger by the tail.

Automobile airbags are pillowlike cushions that protect passengers during head-on crashes. However nobody wants to ride all the time with a huge balloon on their laps. The idea is to keep them folded up until they are needed. But at the moment of an accident, they are needed immediately. The trick is to expand the bags with split second timing before the passenger bumps into any solid objects.

The airbags obviously need to be commanded when to expand. Tiny sensors slide forward when a car suddenly stops. The impact causes tiny balls to touch electrical contacts. This completes an electrical circuit so that current flows to a device which heats up enough to ignite an explosive charge which then ignites pellets of sodium azide. These pellets explosively release nitrogen gas which expands the airbag. The whole process from impact to inflation is designed to take about 0.0003 seconds. This almost seems like a fast-forward “fire fire burn stick, stick stick beat dog, dog dog bite pig, pig pig jump over the stile so that I will get home tonight!!”

Back to the airbags …. It is obvious that the sensor must be sensitive but discriminating. If it expands at inappropriate times, people would refuse to have them in their cars. On the other hand, if the gas expands too slowly, the device would not be any use.

These airbags remind me of some microscopic fungi that use similar techniques, not for safety, but to trap cute unsuspecting nematodes (eelworms) in the soil. Plant lovers dislike eelworms intensely because they do nasty things to plant roots. Certain fungi however love to digest eelworm insides. But how is a fungus to catch slippery, sneaky eelworms? These fungi form short branches made up of three cells that form a ring like a noose. When an eelworm happens to poke its front end through a ring, within 0.1 second the ring cells enormously expand. The eelworm is trapped and doomed. It appears that a rubbing motion on the inside of the ring stimulates these cells to garrote the worm. Precisely how the three cells respond so quickly however, remains a mystery. The response is not quite so rapid as our modern airbags but it is perfect for catching eelworms.

Naturally you understand why I think of tiny fungi when I sit in our beautiful new minivan. Our modern inventions are fine, but they aren’t exactly original. We are just imitators of the Creator of all nature.

October 1997

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