Almost no germ is unconditionally dangerous to man; its disease-producing ability depends upon the body's resistance.

Nothing erases unpleasant thoughts more effectively than conscious concentration on pleasant ones.

To make a great dream come true, you must first have a great dream.

Even after the greatest defeats, the depressing thought of being a failure is best combated by taking stock of all your past achievements.

The healthiest of all human emotions is gratitude.

Indeed, not all attacks-especially the bitter and ridiculing kind leveled at Darwin-are offered in good faith, but for practical purposes it is good policy to assume that they are.

The true scientist never loses the faculty of amazement.