Chapter 3 : Pasteur's First Steps Toward Biology

Abstract:

Louis Pasteur’s first fractionation of racemic acid of tartaric acid into its two isomeric components was the painstaking process of separating the crystals under the microscope according to the orientation of their facets. Pasteur asked himself whether the two isomeric components of the solution, the half which rotated light to the left and the half which rotated it to the right, would be differently affected by the mold. He investigated the optical activity of a solution of paratartrate in which a fungus had grown, and found, to his great excitement, that the solution became more active optically with time. He proved that only one of the components was consumed, whereas the other component was spared. This observation led to an entirely novel and convenient method for the separation of the two isomeric forms by means of the mold, but more importantly it led Pasteur’s mind into new channels that were to take him, and science, into completely uncharted territory. Although we cannot develop here the implications of the fact that biological activity is dependent on molecular structure, we must deal further with the very direct and profound influence that this phenomenon had on Pasteur’s scientific life.