The digestive canal represents a tube passing through the entire organism and communicating with the external world, i.e. as it were the external surface of the body, but turned inwards and thus hidden in the organism.

Science demands from a man all his life. If you had two lives that would not be enough for you. Be passionate in your work and in your searching.

Learn the ABC of science before you try to ascend to its summit.

But man has still another powerful resource: natural science with its strictly objective methods.

Don't become a mere recorder of facts, but try to penetrate the mystery of their origin.

Do not become archivists of facts. Try to penetrate to the secret of their occurrence, persistently search for the laws which govern them.

Gradualness, gradualness, and gradualness. From the very beginning of your work, school yourself to severe gradualness in the accumulation of knowledge.