Without theory, practice is but routine born of habit. Theory alone can bring forth and develop the spirit of invention. ... [Do not] share the opinion of those narrow minds who disdain everything in science which has not an immediate application. ... A theoretical discovery has but the merit of its existence: it awakens hope, and that is all. But let it be cultivated, let it grow, and you will see what it will become.

Whatever your career may be, do not let yourselves become tainted by a deprecating and barren scepticism.

My opinion - nay more, my conviction - is that, in the present state of science, as you rightly say, spontaneous generation is a chimera; and it would be impossible for you to contradict me, for my experiments all stand forth to prove that spontaneous generation is a chimera.

The grandeur of the acts of men are measured by the inspiration from which they spring.

I am on the edge of mysteries and the veil is getting thinner and thinner.

Posterity will one day laugh at the sublime foolishness of the modern materialistic philosophy. The more I study nature, the more I stand amazed at the work of the Creator. I pray while I am engaged at my work in the laboratory.

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.