Physical pain is easily forgotten, but a moral chagrin lasts indefinitely.

It is idle to dispute with old men. Their opinions, like their cranial sutures, are ossified.

The brain is a world consisting of a number of unexplored continents and great stretches of unknown territory.

What a cruel irony of fate, to pair together, like Siamese twins united by the shoulders, scientific adversaries of such contrasting character!

In the study of this membrane [the retina] I for the first time felt my faith in Darwinism (hypothesis of natural selection) weakened, being amazed and confounded by the supreme constructive ingenuity revealed not only in the retina and in the dioptric apparatus of the vertebrates but even in the meanest insect eye. ... I felt more profoundly than in any other subject of study the shuddering sensation of the unfathomable mystery of life.

As long as our brain is a mystery, the universe, the reflection of the structure of the brain will also be a mystery.

Nothing inspires more reverence and awe in me than an old man who knows how to change his mind.