Louis Pasteur (1822-1895) in 1886.

Pasteur will use the polarimetre for his precious crystals.  He knows that there exists a constant relation between the position of a crystal’s facettes and the direction towards which the polarized light is deviated.  Why such an interest in crystals?  To study two substances which are the object of a debate at the heart of the epoch’s Science and Industry:  tartric acid and paratartric acid, which both crystallize.  The first, discovered in the tartar of wine casks, then serves for the impregnation of cloth.  The second had been discovered by accident by a manufacturer who was preparing tartric acid.  Their difference is their solubility and it is a big difference for the industrial world.

It is an economical question, but these minuscule crystals are going to open the way for the little Arbois provincial, and will lead him, many years later, to create the Institute which will bear his name.  Ironically, the great adventure of modern Medicine is therefore going to begin inside wine casks, on the hunt for a crystal:  that of paratartric acid.  This is why it is indispensable to well understand what will follow, for young Pasteur’s discovery constitutes not only the basis of a new Science, but these crystals are going to open the field of yeasts, the yeasts the field of microbes, the microbes that of vaccines.  He approaches this research under the empire of certain ideas.  He often likes to say that Nature is dissymmetrical.  Pasteur sees the dissymmetry of molecules everywhere in the Universe:

“The Universe is a dissymmetrical whole […]  for if one could place in front of a mirror the bodies which compose the solar system, moving with their own movements, one would have in the mirror an image which is not superposable to reality.  The movement of solar light itself is dissymmetrical.  […]  Terrestrial magnetism, the opposition which exists between the boreal and austral poles in a magnet, that which is offered to us by the two positive and negative electricities, are only the results of dissymmetrical actions and movements.”

To give an example, if one places a simple staircase in front of a mirror, its reflection is a twin, superposable to the original.  But if one places a winding staircase which turns to the right in front of this same mirror, the reflection would show another staircase whose steps turn to the left.

By multiplying the experiments with the microsope and the polarimetre, the young scholar notices that the tartric acid crystals, tartrate, possess little facettes which are directed to the right on half of their ridges, making them dissymmetrical.  This detail had not been noticed by anybody.  So, if one places one of these crystals in front of a mirror, the image that appears in it cannot be superposed on it.  To conclude, the crystal and its image seem to be twin images a priori, but like hands, or like gloves;  the image of the right hand not being superposable to that of the left hand.

“The left-hand glove does not fit on the right hand”,

underlines Pasteur to illustrate his words.  Backed by these principles, he suspects that the dissymmetry of the crystals’ forms corresponds to the dissymmetry of the molecules which compose them, thereby changing their chemical function.  With an anxious eye, he then observes paratartric acid in the polarimetre, and exclaims:

“All is revealed!  The paratartic crystals also carry little facettes, but some are directed to the right and others to the left.  Paratartar is therefore a mixture of equal parts of  ‘left’ tartrate crystals and ‘right’ tartrate crystals.”

Pasteur communicates his discovery to the Academie des sciences on 22 May 1848.  On 23 June, there is an insurrection.  Firing erupts at the Pantheon and Rue Soufflot, despite the intervention of some men who have had slavery abolished and the Astronomer Arago, who can be seen negotiating, draped in his tricoloured scarf, between the barricades of the worker insurgents and a squadron of dragoons with drawn sabres.  In November, Pasteur is appointed to the University of Strasbourg, where he acquires a solid reputation as an organizer.  On 10 February 1849, the Rector of the Academy, Monsieur Laurent, receives a letter asking him for the hand of one of his daughters, Marie.  Pasteur speaks in it, among other things, of his ambition to return to Paris when, by his scientific works, he will have acquired a little reputation…

In 1851, the Societe de pharmacie de Paris offers a prize of 1,500 francs – these prizes, discerned by an institution, were frequent and represented a non-negligeable financing of research.  Until then, paratartric acid had only appeared in exceptional fashion inside the vats manufacturing tartric acid.  Two questions are submitted to the wisdom of scholars:

“Do tartars containing paratartric acid, that is to say tartric acid right and left, exist?”

“In what circumstances could tartric acid be transformed into paratartic acid?”

Pasteur works tirelessly on the subject.  Luck, once more, is on his side.

The scholar Mitscherlich announces to him that a manufacturer in Saxe obtains paratartric acid practically whenever he wants from tartars which come from Trieste.  Pasteur takes the decision,

“whatever happens, to go as soon as possible to visit the manufacture, to study tartars on the spot”

and, if he judges it necessary, to go as far as Trieste.  False information:  no paratartar on demand in Saxe.  At the beginning of September, he leaves France for Brussels, Cologne, Leipzig, Dresden and Vienna.  From town to town, he collects information and crystals.  Back in Strasbourg, he experiments, cooks, simmers;  he heats tartric acid, then engages it in a saline combination with a substance coming from quinquina, finally adding some calcium chloride.

On 2 May, a telegramme arrives at Miot’s:

“I transform tartric acid into paratartric acid.”

The prize is won, half of the money will serve to buy laboratory material.  But he is attacked, he is denigrated, people pretend not to understand this tale of crystals that are twins but directed differently:  to the left according to some, to the right according to others.  The impetuous young scholar will then begin his career of Man of Communication.

He has at his side Monsieur Duclaux, who is then starting out in scientific life.  He has conserved the memory of that day when Pasteur, seeing that he has to have the arguments for a demonstration which cannot be questioned, begins by asking for a Carpenter.  A pole of pinewood is cut without delay.  Directed by Louis Pasteur, the Carpenter, armed with a saw, a plane and a file, makes crystals of tartrate in wood, of gigantic size compared to their model.  A layer of paper of different colours is applied onto these giant models, so as to underline things.  A green paper is placed on the hemihedral side, that is, on the side of the crystal which presents modifications in comparison with its twin.  Pasteur then asks the Philanthropic Society of which he is a member that the seance of 8 November 1852 be consecrated to the question of hemihedral cystalline forms.  A few colleagues, seeing him to be very excited, want to dissuade him from this project, in the name of the calm which is suited to the candidate.  He won’t listen to anybody and is seen leaving with a rapid step, along with his provision of coloured wooden crystals.  He will make his demonstration, which will be lively and impetuous.  He tells his adversaries:

“If you know the question, what is your conscience doing?  And if you don’t know it, what business is it of yours?”

Then with one of those about-faces for which he is known and which reveal who he is, he lets fall:

“What’s this all about?  One of the conditions to which we are all more or less exposed throughout our careers.  No bitterness remains about it.  Gone with the wind, in the presence of these so varied, so numerous mysteries that all of us, in different directions, are working to elucidate.  It is true that I employed an unusual means to defend myself against attacks […]  but I hold this method as loyal and sure and full of deference toward you.  Your motto:  ‘Etude et Amitie’ [Study and Friendship] would not condemn it.”

Finally, reporting his thoughts about his masters Biot and Senarmont, then dead, who had always loved him with deep affection and supported him in his researches for fifteen years, Pasteur concludes:

“Before resolving on the conduct which places me before you, I questioned their memory and tried to revive their advice.  They would not have disavowed me.”

Duclaux will say later:

“He was still all boiling when we went home together on foot to Rue d’Ulm, and I recall having made him laugh by asking him why, all worked-up as he was, he hadn’t concluded by throwing his wooden crystals at his adversaries’ heads!

And Duclaux comments:

“Pasteur was lucky, for the tartrates are those which present to the highest degree of simplicity the phenomena toward which his young scholar’s ambition was directed.  With other salts, he would have had to search much longer to find less clear things, but he would have finished by finding them.”

From these studies of dissymmetry, would be born a new Science, twenty years later, a direct consequence of these works, Stereochemistry or Chemistry in space.  It seems that Pasteur possessed the gift of shedding light on all that he touched.

***

To be continued.

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