Well, once I gave the whole affair over to the Lord and stopped trying to take care of it myself, He took care of it.
Quigley came home from his walk with Stu last night just fine, and Stu had gotten another stool sample, similar to the one I had, but in more quantity. Quigley drank and we gave him a bit of Pepto-Bismol as per Internet advice. Then he ate a small bit of rice and chicken, and was much more alert and lively than he'd been all day, playing around and generally being a nice dog. Right before bed he ate another bit of rice and chicken and we decided we didn't need to bring him in this morning (Thursday).
I do think, however, based on the way he's acting today, that he really wasn't feeling well yesterday and was indeed more lethargic than normal. Today he's been very interested in food, hanging around the kitchen, pressing himself against me as he tries to get close to the counter, pouncing on bits of ice if they fall from the freezer, none of which he did yesterday. Today I've already had to lock him in his crate for chewing on the rug, and just now had to chase him out of the office for trying to chew the cardboard boxes of my bookmarks. Whereupon he went outside and wrestled with a large, plastic dog-biscuit can. Again, not how he had behaved yesterday. He's also eaten three times already, and ends by looking for more.
Yesterday, he literally just lay around, getting up only to change rooms. When I put him outside, he lay down where he was.
Also, I have to fill in a bit of back story regarding my experiences with dogs and diarrhea. Our first dog got colonitis one summer when we were staying in Flagstaff -- squirted puddles of bloody diarrhea and had to spend a couple days in the hospital. Our third dog had bloody diarrhea from parvo and had to spend a day in the hospital. Most recently, Bear had diarrhea and vomiting during an acute attack of kidney failure on a Saturday, and I was advised to withhold water and food and wait for the doctor on Monday, when it turned out what I should have done was bring him in immediately for sub-Q fluids. So I'm kinda prepped to get weird about diarrhea that's bloody and doesn't end.
Not that that's any excuse for freaking out, just that I can see I have a weakness there. Of course I have a bigger weakness in repeatedly thinking I have to solve the problems and head off the disasters I'm envisioning, when I should be bringing them to the Lord.