Newton had been deteriorating slowly over the last month or so and we've had many various tests run to see if the vet could discover what was wrong with him. Last night, he quit eating (even his special dried shrimp with the consistency of styrofoam that he loved so), and he could barely move when we got home from work today.
We were out of tests to run. We had Newton put to sleep this evening.
He was such a good kitty. I'm going to miss him.