AARON BROWN, CNN ANCHOR: There are so many questions that have arisen, just in the last couple of weeks, about anthrax: How it spreads? What to worry about? How to deal with it? How does it get in the air and spread? How did it happen if that anthrax came in a sealed envelope? Well, medical correspondent, Dr. Sanjay Gupta, now -- more on the delivery system for anthrax when the delivery, the anthrax itself, is measured in microns.</s>DR. SANJAY GUPTA, CNN MEDICAL CORRESPONDENT: Well, in order to demonstrate how a powdery substance may have gotten out of an envelope, we took some standard talcum powder and a standard envelope, and sealed it in a standard fashion. Now look, with just a little bit of pressure here on the envelope, you can see quite a bit of the powder actually getting through. That is just with some gentle tapping. Typically, an envelope like this would actually find its way in a post office and eventually through a mail sorter. Now what's really remarkable here is that this powder is getting not just through the sides of the envelope, but actually through the paper of the envelope itself. Why is that? The porous size of most paper is typically about 100 microns. That means the actual pores are 100 microns in size. That's a strand of -- a thickness of hair. The powder is about 30-40 microns in size, less than half. And the bacterial anthrax spores that we have been hearing so much about that cause inhalational anthrax are typically one to five microns in size. You can't see them. They're too small to be seen by the naked eye. Is this how the powdery substance may have gotten out of an envelope and contaminated a postal office? We don't know, but it is a possibility. Dr. Sanjay Gupta, CNN, Atlanta.
How Could Anthrax Spread Through a Sealed Envelope?