The investigator should have a robust faith - and yet not believe.

First causes are outside the realm of science.

Descriptive anatomy is to physiology what geography is to history, and just as it is not enough to know the typography of a country to understand its history, so also it is not enough to know the anatomy of organs to understand their functions.

Even mistaken hypotheses and theories are of use in leading to discoveries. This remark is true in all the sciences. The alchemists founded chemistry by pursuing chimerical problems and theories which are false. In physical science, which is more advanced than biology, we might still cite men of science who make great discoveries by relying on false theories.

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

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.

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.