Slimy Lettuce Leaves

[idquest]

I started to make smoothies recently with leafy greens like red leaf lettuce, other kinds of lettuce, some spinach-like chinese leaves. What I've noticed is that when I wash the leaves they become sort of slimy as if their surface produces some kind of mucus. I remember watching/reading Dr. Mercola blog that this kind of mucus is a preservative to keep the leaves fresh. But I felt Dr. Mercola wasn't sure himself this is correct.

What's your take on this? What is this mucus, is it dangerous? Is it related somehow to oxalates? To preservatives?

[SunshineMN]

Yes, I noticed both red and green leaf lettuce feel just a tad slimy when washed. I'm not sure it's anything bad though. I assumed it was just because the leaves have a different texture than say romaine does. I've never looked at lettuce leaves under a microscope though to see what the surface really looks like. I don't worry about it though.