The character of Biot, a puzzle to Sainte Beuve, seems easier to understand after reading those letters, written in a small conscientious hand. The great critic wrote: “Who will give us the secret key to Biot’s complex nature, to the curiosities, aptitudes, envies, prejudices, sympathies, antipathies, folds and creases of every kind in his character?” Even with no other documents, the history of his relations with Pasteur would throw light upon this nature, not so “complex” after all. From the day when Pasteur worked out his first experiment before Biot, at first suspicious, then astonished and finally touched to the heart, until the period of absolute mutual confidence and friendship, we see rising before us the image of this true scientist, with his rare independence, his good-will towards laborious men and his mercilessness to every man who, loving not Science for its own sake, looked upon a discovery as a road to fortune, pecuniary or political. He loved both science and letters, and, now that age had bent his tall form, instead of becoming absorbed in his own recollections and the contemplation of his own labours, he kept his mind open, happy to learn more every day and to anticipate the future of Pasteur. During the vacation of 1851 Pasteur came to Paris to bring Biot the results of new researches on aspartic and malic acids, and he desired his father to join him in order to efface the sad impression left by his former journey in 1838. Biot and his wife welcomed the father and son as they would have welcomed very few friends. Touched by so much kindness, Joseph Pasteur on his return in June wrote Biot a letter full of gratitude, venturing at the same time to send the only thing it was in his power to offer, a basket of fruit from his garden. Biot answered as follows: “Sir, my wife and I very much appreciate the kind expressions in the letter you have done me the honour of writing me. Our welcome to you was indeed as hearty as it was sincere, for I assure you that we could not see without the deepest interest such a good and honourable father sitting at our modest table with so good and distinguished a son. I have never had occasion to show that excellent young man any feelings but those of esteem founded on his merit, and an affection inspired by his personality. It is the greatest pleasure that I can experience in my old age, to see young men of talent working industriously and trying to progress in a scientific career by means of steady and persevering labour, and not by wretched intriguing. That is what has made your son dear to me, and his affection for me adds yet to his other claims and increases that which I feel for him. We are therefore even with one another. As to your kindness in wishing that I should taste fruit from your garden, I am very grateful for it, and I accept it as cordially as you send it.”