Music is the effort we make to explain to ourselves how our brains work. We listen to Bach transfixed because this is listening to a human mind.

Viewed from the distance of the moon, the astonishing thing about the earth, catching the breath, is that it is alive. The photographs show the dry, pounded surface of the moon in the foreground, dry as an old bone. Aloft, floating free beneath the moist, gleaming, membrane of bright blue sky, is the rising earth, the only exuberant thing in this part of the cosmos.

Sometimes you get a glimpse of a semicolon coming, a few lines farther on, and it is like climbing a steep path through woods and seeing a wooden bench just at a bend in the road ahead, a place where you can expect to sit for a moment, catching your breath.

Medical knowledge and technical savvy are biodegradable. The sort of medicine that was practiced in Boston or New York or Atlanta fifty years ago would be as strange to a medical student or intern today as the ceremonial dance of a !Kung San tribe would seem to a rock festival audience in Hackensack.

Maybe there is a single spot, just one, where living organisms are holed up. Maybe so, but if so this would be the strangest thing of all, absolutely incomprehensible. For we are not familiar with this kind of living. We do not have solitary, isolated creatures. It is beyond our imagination to conceive of a single form of life that exists alone and independent, unattached to other forms.

It is in our genes to understand the universe if we can, to keep trying even if we cannot, and to be enchanted by the act of learning all the way.

Cats are a standing rebuke to behavioral scientists wanting to know how the minds of animals work. The mind of a cat is an unscrutable mystery.