To experiment is to disturb certain natural phenomena in order to establish their nature or cause. To observe is to examine things as they pass in natural sequence. Whatever means on may use, microscopes, telescopes, one only observes.

Translated by Hebbel H. Hoff, Lucienne Guillemin and Roger Guillemin, The Cahier Rouge of Claude Bernard (p. 35), Schenkman Publishing Co. 1967