Proof that a given condition always precedes or accompanies a phenomenon does not warrant concluding with certainty that a given condition is the immediate cause of that phenomenon. It must still be established that when this condition is removed, the phenomen will no longer appear.

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

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.

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.

Mediocre men often have the most acquired knowledge

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

It has often been said that, to make discoveries, one must be ignorant. This opinion, mistaken in itself, nevertheless conceals a truth. It means that it is better to know nothing than to keep in mind fixed ideas based on theories whose confirmation we constantly seek, neglecting meanwhile everything that fails to agree with them.