Researches on the molecular dissymmetry of natural organic products : presented to the Chemical Society of Paris, January 20 and February 3, 1860 / by L. Pasteur ; translated from "Leçons de chimie professées en 1860" by W.S.W. Ruschenberger.

  • Pasteur, Louis, 1822-1895.
Date:
[1862]
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Licence: Public Domain Mark

Credit: Researches on the molecular dissymmetry of natural organic products : presented to the Chemical Society of Paris, January 20 and February 3, 1860 / by L. Pasteur ; translated from "Leçons de chimie professées en 1860" by W.S.W. Ruschenberger. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    All artificial products of the laboratory and all mineral species have a superposable image. On the contrary, most of the natural organic products, (I might say all, if I had to name only those which play an essential part in the phenomena of animal and vegetable life,) all products essential to life are dissymmetric and of the dissymmetry which causes their image to be non-superposable. Before proceeding further, I desire to set aside some objec- tions which cannot fail to present themselves to your minds. IV. Quartz, you will say at once ? We have seen in the last lecture that quartz possesses the two characters of dissymmetry, the hemihedrity in form observed by Hauy, and the rotary phenomenon discovered by Arago. Nevertheless, all molecular dissymmetry is absent in quartz. To understand it, let us ad- vance a little further in the knowledge of the phenomena we are considering. We shall find, moreover, the explanation of the analogies and differences already previously indicated between quartz and natural organic products. Permit me to describe roughly, though in the main accurately, the structure of quartz and that of natural organic products. Imagine a winding stair, the steps of which shall be cubes, or any other object with a superposable image. Destroy the stair, and the dissymmetry will have disappeared. The dissymmetry of the stair was the result only of the mode of putting together its elementary steps. Such is quartz. The crystal of quartz is the stair all built. It is hemihedric. For this reason it acts on polarized light. But let the crystal be dissolved, melted, its physical structure destroyed in any manner, and its dissymmetry is suppressed, and with it all action on polarized light, as would happen, for example, in a solution of alum, a liquid formed of molecules of a cubic structure distributed without order. Imagine, on the contrary, the same winding stair formed of irregular tetrahedrons for steps. Destroy the stair, and the dissymmetry will still exist, because you have to deal with an assemblage of tetrahedrons. They may be in any position, but each one of them will have its proper dissymmetry, neverthe- less. Such are organic bodies in which all the molecules have