Although of course I am aware that it changes colour in a jar. But we know why, surely? The heavier melancholic elements in the blood sink, making the top lighter and the bottom darker.'Not so,' I said firmly. 'Cover the jar, and the colour does not change. And I can find no explanation of how such separation could occur in the lungs. But when it emerges from the lungs - at least, this is the case in cats - it is very much lighter in colour than when it goes in, indicating that some darkness is withdrawn from it.'I must cut up a cat and see for myself. A live cat, was it?'It was for a while.