“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.”

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.

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.

The eloquence of a scientist is clarity; scientific truth is always more luminous when its beauty is unadorned than when it is tricked out in the embellishments with which our imagination would seek to clothe it.

In science, the best precept is to alter and exchange our ideas as fast as science moves ahead.

We must remain, in a word, in an intellectual disposition which seems paradoxical, but which, in my opinion, represents the true mind of the investigator. We must have a robust faith and yet not believe.

True science teaches us to doubt and, in ignorance, to refrain.

Those who do not know the torment of the unknown cannot have the joy of discovery.

The doubter is a true man of science: he doubts only himself and his interpretations, but he believes in science.

Obervation is a passive science, experimentation is an active science.