New development: I just referred an acquaintance of mine to this doctor, and she will probably call him. Anyway, as our first contact since the meeting in my post, I emailed him with a simple greeting, hoping that he was doing well, etc., and then the next paragraph detailed my acquaintance's recent medical issues. My closing was a whimsical reference to his semi-diagnosis during our conversation, and that was it. Nothing forward or flirtatious at all; however, I did venture to make contact, which was big for me, if you have read my earlier posts.
Yes, he responded after two days and graciously thanked me for the referral and encouraged her to call him before she made any decisions. His P.S. was a recommendation to have my spine checked, which addressed my whimsical closing in my message, and then he put a winking emoticon next to it.
So now there are two benign pieces of communication after about six weeks of no contact. I guess I didn't need anything more benign in this mix, but I am sure you responders will tell me that I asked for this in my rather "professional only" message. He responded in kind. Hm-m...