poison ivy

I have a bad habit. When I walk through a place with lots of bushes and trees, I'll absentmindedly
tear a leaf off a tree or bush and tear it up slowly while I'm walking.
I don't like that I do it, because it seems rather destructive. I just
don't think about it much.

In CA, we have poison oak. In the summer it looks like this:
I'm very careful not to touch it, as I'm quite allergic. I had it
bad once in 7th grade, and I've been very careful since.

In Pittsburgh, they don't have poison oak. They have poison ivy. I didn't know
what it looks like until this week, when I started getting rashes
on my wrists, neck and back. For those of you who are moving from CA to the east, this is what poison ivy looks like:
It's really not a good idea to pick these leaves and tear them
to little pieces. Take it from me.

It's actually fascinating how it works. The oil from the leaves somehow modifies the proteins of the skin cells into which it comes in contact. The proteins it modifies are responsible for notifying your immune system that the cell is indeed part of your body, and
is not a foreign object. Once the oil manipulates the protein, your body can no longer tell
that your own skin is part of your body, and starts attacking it. Miracles of evolution abound.

PS: If you've never read them, Steven Jay Gould and Loren Eisley's books are filled with such facts and anecdotes.