A fact in itself is nothing. It is valuable only for the idea attached to it, or for the proof which it furnishes.

Put off your imagination, as you put off your overcoat, when you enter the laboratory. Put it on again, as you put on your overcoat, when you leave.

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

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

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.

In the patient who succumbed, the cause of death was evidently something which was not found in the patient who recovered; this something we must determine, and then we can act on the phenomena or recognize and foresee them accurately. But not by statistics shall we succeed in this; never have statistics taught anything, and never can they teach anything about the nature of the phenomenon.

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.