Describing laughter: The sound is produced by a deep inspiration followed by short, interrupted, spasmodic contractions of the chest, and especially the diaphragm... the mouth is open more or less widely, with the corners drawn much backwards, as well as a little upwards; and the upper lip is somewhat raised.

One day, on tearing off some old bark, I saw two rare beetles, and seized one in each hand. Then I saw a third and new kind, which I could not bear to lose, so I popped the one which I held in my right hand into my mouth. Alas! it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as was the third one.

Everything in nature is the result of fixed laws.

I have deeply regretted that I did not proceed far enough at least to understand something of the great leading principles of mathematics, for men thus endowed seem to have an extra sense.

May we not suspect that the vague but very real fears of children, which are quite independent of experience, are the inherited effects of real dangers and abject superstitions during ancient savage times?

The most important factor in survival is neither intelligence nor strength but adaptability.

Man, wonderful man, must collapse, into nature's cauldron, he is no deity, he is no exception.