“We must alter theory to adapt it to nature, but not nature to adapt it to theory.‎”

The joy of discovery is certainly the liveliest that the mind of man can ever feel.

The experimenter who does not know what he is looking for will not understand what he finds.

The better educated we are and the more acquired information we have, the better prepared shall we find our minds for making great and fruitful discoveries.

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.

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

Everything is poisonous, nothing is poisonous, it is all a matter of dose.

Effects vary with the conditions which bring them to pass, but laws do not vary. Physiological and pathological states are ruled by the same forces; they differ only because of the special conditions under which the vital laws manifest themselves.

Priestley said that each discovery we make shows us many others that should be made.

With the aid of these active experimental sciences man becomes an inventor of phenomena, a real foreman of creation; and under this head we cannot set limits to the power that he may gain over nature through future progress of the experimental sciences.

The minds that rise and become really great are never self-satisfied, but still continue to strive.

But while I accept specialization in the practice, I reject it utterly in the theory of science.

Science does not permit exceptions.

All the vital mechanisms, varied as they are, have only one object, that of preserving constant the conditions of life in the internal environment.

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.

In the philosophic sense, observation shows and experiment teaches.