A long shot...
When I was a child, my mum had a black and white picture book which she had bought in the Fifties all about cats. I loved looking at that book and would love to find it again but have absolutely no idea what it was called or who published it.
The one thing that I can remember was that one of the first pictures in the book had a picture of a rather elderly cat and the picture had been titled "Nunc dimitis." Not much to go on, but the right person would know, I'm sure...