necessary: water, candied sugar, tartaric acid, nitrate of ammonia, phosphate of ammonia, carbonate of potash, carbonate of magnesia, sulphate of ammonia, sulphate of zinc, sulphate of iron, and silicate of potash. He now studied the part played by each of those elements, varying his quantities, taking away one substance and adding another, and obtained some very curious results. For instance, the aspergillus was extraordinarily sensitive to the action of zinc; if the quantity of zinc was reduced by a few milligrams the vegetation decreased by one-tenth. Other elements were pernicious; if Raulin added to his liquid 1/1600000 of nitrate of silver, the growth of the fungus ceased. Moreover, if he placed the liquid in a silver goblet instead of a china saucer, the vegetation did not even begin, “though,” writes M. Duclaux, analysing this fine work of his fellow student, “it is almost impossible to chemically detect any dissolution of the silver into the liquid. But the fungus proves it by dying.” In this thesis, now a classic, which only appeared in 1870, Raulin enumerated with joyful gratitude all that he owed to his illustrious master--general views, principles and methods, suggestive ideas, advice and encouragement--saying that Pasteur had shown him the road on which he had travelled so far. Pasteur, touched by his pupil’s affection, wrote to thank him, saying: “You credit me with too much; it is enough for me that your work should be known as having been begun in my laboratory, and in a direction the fruitfulness of which I was perhaps the first to point out. I had only conceived hopes, and you bring us solid realities.” In April, 1871, Pasteur, preoccupied with the future, and ambitious for those who might come after him, wrote to Claude Bernard: “Allow me to submit to you an idea which has occurred to me, that of conferring on my dear pupil and friend Raulin the Experimental Physiology prize, for his splendid work on the nutriment of mucors, or rather of a mucor, the excellence of which work has not escaped you. I doubt if you can find anything better. I must tell you that this idea occurred to me whilst reading your admirable report on the progress of General Physiology in France. If therefore my suggestion seems to you acceptable, you will have sown the germ of it in my mind; if you disapprove of it I shall make you partly responsible.” Claude Bernard hastened to reply: “You may depend upon my support for your pupil M. Raulin. It will be for me both a pleasure and a duty to support such excellent work and to glorify the method of the master who inspired it.” In his letter to Claude Bernard, Pasteur had added these words: “I have made up my mind to go and spend a few months at Royat with my family, so as to be near my dear Duclaux. We shall raise a few grammes of silkworm seed.”