Louis Pasteur: His Life and Labours

by René Vallery-Radot

The work of Pasteur, demonstrating that fermentation was always dependent on the life of a microscopic organism, continued without interruption. One of the most remarkable of his researches is that which relates to the fermentation of the tartrate of lime. The demonstration of life and of fermentation without free oxygen is in this paper carried to the utmost limits of experimental rigour and precision.

III.

But there is still another class of chemical phenomena where the life without air of microscopic organisms is fully shown. Pasteur proved that in the special fermentation which bears the name of putrefaction the primum movens of the putrefaction resides in microscopic vibrios of absolutely the same order as those which compose the butyric ferment. The fermentation of sugar, of mannite, of gums, of lactate of lime, by the butyric vibrio, so closely resembles the phenomena of putrefaction, that one might call these fermentations the putrefaction of sugar and of the other products.

If it has been thought right to call the fermentation of animal matters putrefaction, it is because at the moment of the decomposition of fibrine, of albumen, of blood, of gelatine, of the substance of the tendons, &c., the sulphur, and even the phosphorus, which enter into their composition give rise to putrid odours, due to the evil-smelling gases of sulphur and phosphorus.

The phenomena of putrefaction being then simply fermentations, differing only in regard to the chemical composition of the fermenting matters, Liebig naturally included them in his general theory of the decomposition of organic matters after death. At a period long antecedent to Pasteur's labours it had been established that there existed in putrefying matters fungi or microscopic animalculæ, and the idea had taken shape that these creatures might have an influence in the phenomena. The proofs were wanting, but the notion of a possible relation remained. We may read in his 'Lessons on Chemistry' with what disdain Liebig mentioned these hypothetical opinions.

'Those who pretend to explain the putrefaction of animal substances by the presence of animalculæ,' he wrote, 'reason very much like a child who would explain the rapidity of the Rhine by attributing it to the violent motions imparted to it in the direction of Bingen by the numerous wheels of the mills of Mayence. Is it possible to consider plants and animals as the causes of the destruction of other organisms when their own elements are condemned to undergo the same decompositions as the creatures which have preceded them? If the fungus is the cause of the destruction of the oak, if the microscopic animalcula is the cause of the putrefaction of the dead elephant, I would ask in my turn what is the cause which determines the putrefaction of the fungus or of the microscopic animalcula when life is withdrawn from these two organisms?'

Thirty-two years later, and after Pasteur had accumulated, during more than twenty years, proof upon proof that the theory of Liebig would not stand examination, a physician of Paris, M. Bouillaud, asked, with the insistent voice of a querulous octogenarian: 'Let M. Pasteur then tell us here, in presence of the Académie de Médecine, what are the ferments of the ferments.'

Before replying to this argument, which Liebig and M. Bouillaud believed to be irrefutable, Pasteur, wishing to mark all the phases of the phenomena, expounded in a short preamble the part played by atmospheric oxygen in the destruction of animal and vegetable matters after death. It is easy to understand, indeed, that fermentation and putrefaction only represent the first phase of the return to the atmosphere and to the soil of all that has lived. Fermentations and putrefactions give rise to substances which are still very complex, although they represent the products of decomposition of fermentable matters. When sugar ferments, a large proportion of it becomes gas; but alongside of the carbonic acid gas which is formed, and which is, indeed, a partial return of the sugar to the atmosphere, new substances, such as alcohol, succinic acid, glycerine, and materials of yeast, are produced. When the flesh of animals putrifies, certain products of decomposition, also very complex, are formed with the vapour of water and the other gases of putrefaction. Where, then, does nature find the agents of destruction of these secondary products?

The great fact of the destruction of animal and vegetable matters is accomplished by slow combustion, through the appropriation of atmospheric oxygen. Here, again, one must banish from science the preconceived views which assumed that the oxygen seized directly on the organic matter after death, and that this matter was consumed by purely chemical processes. It is life that presides over this work of death.

If fermentation and putrefaction are principally the work of microscopic anaérobies, living without free oxygen, the slow combustion is found very largely, if not exclusively, to depend upon a class of infinitely small aérobies. It is these last which have the property of consuming the oxygen of the air. It is these lower organisms which are the powerful agents in the return to the atmosphere of all which has lived. Mildew, mould, bacteria, which we have already noticed, monads, two thousand of which would go to make up a millimeter, all these microscopic organisms are charged with the great work of re-establishing the equilibrium of life by giving back to it all that it has formed.