Researches on the molecular asymmetry of natural organic products / by Louis Pasteur (1860).

  • Pasteur, Louis, 1822-1895.
Date:
1905
    that there is only a single case in which the right mole¬ cules differ from the left, the case where they are sub¬ mitted to influences of an asymmetric character. Do these asymmetric actions, possibly placed under cosmic influences, reside in light, in electricity, in magnetism, or in heat ? Can they be related to the motion of the earth, or to the electric currents by which physicists explain the terrestrial magnetic poles? It is not even possible at the present time to express the slightest conjecture in this direction. But I regard as necessary the conclusion that asym¬ metric forces exist at the moment of the elaboration of natural organic products ; forces which would be absent, or ineffectual, in the reactions of our laboratories either on account of the violent course of these phenomena, or because of some other unknown circumstance. XII. We now reach a final experiment which does not yield in interest to any of those which precede, in respect to the manifest proof which it will give us of the influence of asymmetry in the phenomena of life. We have just seen asymmetry intervening to modify chemical affinities; but the reactions involved were purely inorganic, artificial, and we know all the prudence that must be observed in the application of the results of the laboratory to the phenomena of life. On this account I kept to myself almost all the views expressed in this Lecture till the moment that I recognised in the most certain manner that molecular asymmetry exhibited itself as a modifier, no longer of the reactions of inorganic nature, but of those of physiological character, in fermentations. Here is the remarkable phenomenon to which I refer : It had long been known, from the observation of a
    German manufacturer of chemical products, that the impure tartrate of lime of the works, mixed with organic matters, when left under water in summer, could ferment, giving various products. Knowing this, I set the ordinary right tartrate of ammonia to ferment in the following manner. I took the very pure crystallised salt, dissolved it, adding to the liquor a clear solution of albumenoid matter. One gram of dry albumenoid matter was sufficient for one hundred grams of tartrate. Very often it happens that the liquid ferments spontaneously when placed in an oven. I say very often ; but it may be added that this will always take place if we take care to mix with the liquid a very small quantity of one of those liquids with. which we have succeeded in obtaining spontaneous fermentation. So far there is nothing peculiar; it is a tartrate fer¬ menting. The fact is well known. But let us apply this method of fermentation to para- tartrate of ammonia, and under the above conditions it ferments. The same yeast is deposited. Everything shows that things are proceeding absolutely as in the case of the right tartrate.' Yet if we follow the course of the operation with the help of the polarising apparatus, we soon discover profound differences between the two operations. The originally inactive liquid possesses a sensible rotative power to the left, which increases little by little and reaches a maximum. At this point the fer¬ mentation is suspended. There is no longer a trace of the right acid in the liquid. When it is evaporated and mixed with an equal volume of alcohol it gives imme¬ diately a beautiful crystallisation of left tartrate of ammonia. Let us note, in the first place, two distinct things in this phenomenon. As in all fermentation properly so called, there is a substance which is changed chemically,
    and correlatively there is a development of a body pos¬ sessing the aspect of a mycodermic growth. On the other hand, and it is this which it is important to note, the yeast which causes the right salt to ferment leaves the left salt untouched, in spite of the absolute identity in physical and chemical properties of the right and left tartrates of ammonia as long as they are not subjected to asymmetric action. Here, then, the molecular asymmetry proper to organic substances intervenes in a phenomenon of a physiological kind, and it intervenes in the role of a modifier of chemical affinity. It is not at all doubtful that it is the kind of asymmetry proper to the molecular arrangement of left tartaric acid which is the sole and exclusive cause of the difference from the right acid, which it presents in relation to fermentation. Thus we find introduced into physiological principles and investigations the idea of the influence of the mole¬ cular asymmetry of natural organic products, of this great character which establishes perhaps the only well marked line of demarcation that can at present be drawn between the chemistry of dead matter and the chemistry of living matter. XIII. Such, gentlemen, are in co-ordinated form the investi¬ gations which I have been asked to present to you. You have understood, as we proceeded, why I entitled my exposition, “ On the Molecular Asymmetry of Natural Organic Products.” It is, in fact, the theory of molecular asymmetry that we have just established, one of the most exalted chapters of the science. It was completely un¬ foreseen, and opens to physiology new horizons, distant, but sure. I hold this opinion of the results of my own work with-
    out allowing any of the vanity of the discoverer to mingle in the expression of my thought. May it please God that personal matters may never be possible at this desk. These are like pages in the history of chemistry which we write successively with that feeling of dignity which the true love of science always inspires. GEO. STEWART AND CO., PRINTERS, EDINBURGH
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