Bill - I fear you're being a bit narrow in your thinking about this issue.

Books are one way to gather knowledge and perpetuate it, but not the only way. As Helen points out, the oral tradition is a very important way of doing this, and in fact has probably perpetuated far more knowledge over the course of our existence than books, given its much longer track record.

Midwives may not have had access to the means of producing books, whether those means be literacy, or money, or access to the educated circles that publish, or what have you. Lacking any of these key things would have required them to find other means of carrying on their knowledge.

There's more than one way to skin a cat, Dr. Bill.