hemihedral faces; but he had found none on the racemates. Conceiving that this aspect of crystals might be an index of their molecular structure, he reasoned that the diverse optical behaviors of solutions of tartaric and racemic acids might be explained by a structural law. On fire with this new idea, he carefully examined a lot of tartrate crystals, and found, as he had anticipated, that each had hemi-hedral facets. He turned now to racemate crystals, expecting to find them destitute of hemihedrism. Imagine his disappointment, therefore, upon finding that here also each crystal distinctly displayed hemihedrism. But upon laboriously going over his work again he discovered a fact that had previously escaped his notice, namely, that the half-form facets of tartaric acid were all turned toward the right while those of the racemates were half right-handed and half left-handed. A new idea flashed into his mind. Carefully picking apart the two kinds of racemate crystals, he made a solution of each and, with anxious mind and throbbing heart, applied the polariscope. The solution of right-handed crystals deflected the beam to the right. They were pure tartaric acid. The solution of left-handed crystals deflected the beam to the left. They were a new acid—lævo tartaric acid. He mixed his solutions in equal proportions. The mixture did not affect the beam. It was racemic acid.
His excitement was so great that he could not look through the instrument again. Like Archimedes, he exclaimed "I have found it," and rushed into the corridor, where he met an assistant whom he embraced in a transport of joy.
This was one of the most illuminating discoveries known to the history of chemistry up to that time. Measured by its ultimate results, it is doubtless the most far-reaching discovery ever made. Developing in one direction, it was the germ of a new science—stereo-chemistry; in another it transformed medicine and agriculture from empirical practises into true sciences; and incidentally it enriched the world by a number of other discoveries of unparalleled practical value. Done at the age of twenty-five, this first great work of Pasteur's was a prophecy of that brilliant career throughout which he continued to manifest the same marvelous capacity for seeing the unseeable. It led to his appointment at once as professor of chemistry in the college of Dijon.
Finding that the duties of this position consumed all his time in teaching, he asked the government for a transfer to some place which would admit of his going on with research. Quite unexpectedly to himself, he was sent at the beginning of 1849 to the University of Strasburg to relieve Bersoz, professor of chemistry there, who desired to go to Paris.
Eealizing fully the value of the vein he had discovered in tartaric acids, he directed his energies along that line. He had found out what para-tartaric, or racemic, acid is; but neither he nor any one else knew
