Thank you very much for the well-wishes and the information. KAK, the website was very useful. Gatsby certainly fits the profile of a FLUTD-prone cat.

The vet needed to use a catheter after all. Apparently I got him there just before he blocked. But she's not finding crystals, so it sounds like it's a matter of finding the right antibiotic to take care of whatever sort of infection he has. The procedure went well, and he's doing fine so far.

Poor fellow will have to spend the weekend there, and they're not open tomorrow so I can't visit. They'll have vets and techs keeping an eye on him, but no public access. I just hope he can come home Monday and gets over this once and for all.

Apparently everyone at the clinic has fallen in love with him. The vet was amazed that she could poke and prod without needing anyone else to hold onto him--he just puts up with it. She said that everyone has been spending time with him because he's just the sweetest cat ever. As long as he's nowhere near another cat, that is.