“A man of science rises ever, in seeking truth; and if he never finds it in its wholeness, he discovers nevertheless very significant fragments; and these fragments of universal truth are precisely what constitutes science.”

It is what we know already that often prevents us from learning.

When entering on new ground we must not be afraid to express even risky ideas so as to stimulate research in all directions. As Priestley put it, we must not remain inactive through false modesty based on fear of being mistaken.

Man can learn nothing unless he proceeds from the known to the unknown.

Theories are like a stairway; by climbing, science widens its horizon more and more, because theories embody and necessarily include proportionately more facts as they advance.

The first requirement in using statistics is that the facts treated shall be reduced to comparable units.

We achieve more than we know. We know more than we understand. We understand more than we can explain.

The stability of the internal medium is a primary condition for the freedom and independence of certain living bodies in relation to the environment surrounding them.

We must never make experiments to confirm our ideas, but simply to control them.

We must keep our freedom of mind, and must believe that in nature what is absurd, according to our theories, is not always impossible.

The goal of scientific physicians in their own science … is to reduce the indeterminate. Statistics therefore apply only to cases in which the cause of the facts observed is still indeterminate.

Science admits no exceptions; otherwise there would be no determinism in science, or rather, there would be no science.

Mediocre men often have the most acquired knowledge. It is in the darker. It is in the darker regions of science that great men are recognized; they are marked by ideas which light up phenomena hitherto obscure and carry science forward.

Experiment is fundamentally only induced observation.

The science of life is a superb and dazzlingly lighted hall which may be reached only by passing through a long and ghastly kitchen.

Our ideas are only intellectual instruments which we use to break into phenomena; we must change them when they have served their purpose, as we change a blunt lancet that we have used long enough.

Now, a living organism is nothing but a wonderful machine endowed with the most marvellous properties and set going by means of the most complex and delicate mechanism.