The greatest disorder of the mind is to let will direct it.

Virulence appears in a new light which cannot but be alarming to humanity; unless nature, in her evolution down the ages (an evolution which, as we now know, has been going on for millions, nay, hundreds of millions of years), has finally exhausted all the possibilities of producing virulent or contagious diseases - which does not seem very likely.

It is not the germs we need worry about. It is our inner terrain.

One does not ask of one who suffers: What is your country and what is your religion? One merely says: You suffer, that is enough for me.

There are no such things as applied sciences, only applications of science.

The greatest derangement of the mind is to believe in something because one wishes it to be so.

Every chemical substance, whether natural or artificial, falls into one of two major categories, according to the spatial characteristic of its form. The distinction is between those substances that have a plane of symmetry and those that do not. The former belong to the mineral, the latter to the living world.