He loved them still, as is proved by an answer from Biot to a proposal of Pasteur’s. In order to spare the old man’s failing sight, Pasteur had the ingenious idea of cutting out of pieces of cork, with exquisite skill, some models of crystalline types greatly enlarged. He had tinted the edges and faces, and nothing was easier than to recognize their hemihedral character. “I accept with great pleasure,” wrote Biot on April 7, “the offer you make me of sending me a small quantity of your two acids, with models of their crystalline types.” He meant the righthand tartaric acid and the lefthand tartaric acid, which Pasteur--not to pronounce too hastily on their identity with ordinary tartaric acid--then called _dextroracemic_ and _lævoracemic_. Pasteur wished to go further; he was now beginning to study the crystallizations of formate of strontian. Comparing them with those of the paratartrates of soda and ammonia, surprised and uneasy at the differences he observed, he once exclaimed, “Ah! formate of strontian, if only I had got you!” to the immense amusement of Bertin, who long afterwards used to repeat this invocation with mock enthusiasm. Pasteur was about to send these crystals to Biot, but the latter wrote, “Keep them until you have thoroughly investigated them.... You can depend on my wish to serve you in every circumstance when my assistance can be of any use to you, and also on the great interest with which you have inspired me.” Regnault and Senarmont had been invited by Biot to examine the valuable samples received from Strasburg, the dextroracemic and lævoracemic acids. Biot wrote to Pasteur, “We might make up our minds to sacrifice a small portion of the two acids in order to reconstitute the racemic, but we doubt whether we should be capable of discerning it with certainty by those crystals when they are formed. You must show it us yourself, when you come to Paris for the holidays. Whilst arranging my chemical treasures, I came upon a small quantity of racemic acid which I thought I had lost. It would be sufficient for the microscopical experiments that I might eventually have to make. So if the small phial of it that you saw here would be useful to you, let me know, and I will willingly send it. In this, as in everything else, you will always find me most anxious to second you in your labours.” This period was all happiness. Pasteur’s father and his sister Josephine came to Strasburg. The proposal of marriage was accepted, the father returned to Arbois, Josephine staying behind. She remained to keep house and to share the everyday life of her brother, whom she loved with a mixture of pride, tenderness and solicitude. In her devoted sisterly generosity, she resigned herself to the thought that her happy dream must be of short duration. The wedding was fixed for May 29.