Without theory, practice is but routine born of habit. Theory alone can bring forth and develop the spirit of inventions.

The artificial products do not have any molecular dissymmetry; and I could not indicate the existence of a more profound separation between the products born under the influence of life and all the others.

After death, life reappears in a different form and with different laws. It is inscribed in the laws of the permanence of life on the surface of the earth and everything that has been a plant and an animal will be destroyed and transformed into a gaseous, volatile and mineral substance.

Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment.

Herrmann Pidoux and Armand Trousseau stated 'Disease exists within us, because of us, and through us', Pasteur did not entirely disagree, 'This is true for certain diseases', he wrote cautiously, only to add immediately: 'I do not think that it is true for all of them'.

To bring one's self to believe in a truth that has just dawned upon one is the first step towards progress; to persuade others is the second.

In the realm of scientific observation, luck is granted only to those who are prepared.