We must doubt the certainty of everything which passes through the senses, but how much more ought we to doubt things contrary to the senses, such as the existence of God and the soul.

He who walks straight rarely falls.

Nothing will be left, Nothing in the air, nothing under the earth, nothing in the waters. All will be exterminated.

The eye, the window of the soul, is the chief means whereby the understanding can most fully and abundantly appreciate the infinite works of Nature; and the ear is second.

The greatest geniuses sometimes accomplish more when they work less.

One day the world will look upon research upon animals as it now looks upon research on human beings.

I am never weary of being useful... In serving others I cannot do enough. No labor is sufficient to tire me.