Chapter VII · 1870—1872 (continued 2)

Old arguments and renewed negations were brought forward, and Pasteur knew well that this was but a reappearance of the old quarrel; he therefore answered by going straight to the point. At the Académie des Sciences, on December 26, 1871, he addressed M. Trécul in these words: “I can assure our learned colleague that he might have found in the treatises I have published decisive answers to most of the questions he has raised. I am really surprised to see him tackle the question of so-called spontaneous generation, without having more at his disposal than doubtful facts and incomplete observations. My astonishment was not less than at our last sitting, when M. Frémy entered upon the same debate with nothing to produce but superannuated opinions and not one new positive fact.”

In his passion for truth and his desire to be convincing Pasteur threw out this challenge: “Would M. Frémy confess his error if I were to demonstrate to him that the natural juice of the grape, exposed to the contact of air, deprived of its germs, can neither ferment nor give birth to organized yeasts?” This interpellation was perhaps more violent than was usual in the meetings of the solemn Academy, but scientific truth was in question. And Pasteur, recognizing the old arguments under M. Frémy’s hemiorganism and M. Trécul’s transformations, referred his two contradictors to the experiments by which he had proved that alterable liquids, such as blood or urine, could be exposed to the contact of air deprived of its germs without undergoing the least fermentation or putrefaction. Had not this fact been the basis on which Lister had founded “his marvellous surgical method”? And in the bitterness given to his speech by his irritation against error, the epithet “marvellous” burst out with a visible delight in rendering homage to Lister.

Pasteur, then in full possession of all the qualities of his genius, was feeling the sort of fever known to great scientists, great artists, great writers: the ardent desire of finding, of discovering something he could leave to posterity. Interrupted by these belated contradictors when he wanted to be going forward, he only restrained his impatience with difficulty.

His old master, Balard, appealed to him in the Académie itself (January 22, 1872), in the name of their old friendship, to disregard the attacks of his adversaries, instead of wasting his time and his strength in trying to convince them. He reminded him of all he had achieved, of the benefits he had brought to the industries of wine, beer, vinegar, silkworms, etc., and alluded to the possibility foreseen by Pasteur himself of preserving mankind from some of the mysterious diseases which were perhaps due to germs in atmospheric air. He ended by urging him to continue his studies peacefully in the laboratory built for him, and to continue the scientific education of young pupils who might one day become worthy successors of Van Tieghem, Duclaux, Gernez, Raulin, etc.... thus forming a whole generation of young scientists instructed in Pasteur’s school.

M. Duclaux wrote to him in the same sense: “I see very well what you may lose in that fruitless struggle—your rest, your time and your health; I try in vain to see any possible advantage.”

But nothing stopped him; neither Balard’s public advice, his pupils’ letters, even J. B. Dumas’ imploring looks. He could not keep himself from replying. Sometimes he regretted his somewhat sharp language, though—in his own words—he never associated it with feelings of hostility towards his contradictors as long as he believed in their good faith; what he wanted was that truth should have the last word. “What you lack, M. Frémy, is familiarity with a microscope, and you, M. Trécul, are not accustomed to laboratories!” “M. Frémy is always trying to displace the question,” said Pasteur, ten months after M. Balard’s appeal.

Whilst M. Frémy disputed, discussed, and filled the Académie with his objections, M. Trécul, whose life was somewhat misanthropical and whose usually sad and distrustful face was seen nowhere but at the Institute, insisted slowly, in a mournful voice, on certain transformations of divers cells or spores from one into the other. Pasteur declared that those ideas of transformation were erroneous; but—and there lay the interest of the debate—there was one of those transformations that Pasteur himself had once believed possible: that of the mycoderma vini, or wine flower, into an alcoholic ferment under certain conditions of existence.

A modification in the life of the mycoderma when submerged had led him to believe in a transformation of the mycoderma cells into yeast cells. It was on this question, which had been left in suspense, that the debate with Trécul came to an end, leaving to the witnesses of it a most vivid memory of Pasteur’s personality—inflexible when he held his proofs, full of scruples and reserve when seeking those proofs, and accepting no personal praise if scientific truth was not recognized and honoured before everything else.

On November 11 Pasteur said: “Four months ago doubts suddenly appeared in my mind as to the truth of the fact in question, and which M. Trécul still looks upon as indisputable.... In order to disperse those doubts I have instituted the most numerous and varied experiments and I have not succeeded through those four months in satisfying myself by irrefragable proofs; I still have my doubts. Let this example show to M. Trécul how difficult it is to conclude definitely in such delicate studies.”

Pasteur studied the scientific point for a long time, for he never abandoned a subject, but was ever ready to begin again after a failure. He modified the disposition of his first tests, and by the use of special vessels and slightly complicated apparatus succeeded in eliminating the only imaginable cause of error—the possible fall, during the manipulations, of exterior germs, that is, the fortuitous sowing of yeast cells. After that he saw no more yeast and no more active alcoholic fermentation; he had therefore formerly been the dupe of a delusion. In his Studies on Beer Pasteur tells of his error and its rectification: “At a time when ideas on the transformations of species are so readily adopted, perhaps because they dispense with rigorous experimentation, it is somewhat interesting to consider that in the course of my researches on microscopic plants in a state of purity I once had occasion to believe in the transformation of one organism into another, the transformation of the mycoderma vini or cerevisiae into yeast, and that this time I was in error; I had not avoided the cause of illusion which my confirmed confidence in the theory of germs had so often led me to discover in the observations of others.”

“The notion of species,” writes M. Duclaux, who was narrowly associated with those experiments, “was saved for the present from the attacks directed against it, and it has not been seriously contested since, at least not on that ground.”

Some failures are blessings in disguise. When discovering his mistake, Pasteur directed his attention to a strange phenomenon. We find in his book on beer—a sort of laboratory diary—the following details on his observation of the growth of some mycoderma seed which he had just scattered over some sweetened wine or beer-wort in small china saucers.

“When the cells or articles of the mycoderma vini are in full germinating and propagating activity in contact with air on a sweetened substratum, they live at the expense of that sugar and other subjacent materials absolutely like the animals who also utilize the oxygen in the air while freeing carbonic acid gas, consuming this and that, and correlatively increasing, regenerating themselves and creating new materials.

“Under those conditions not only does the mycoderma vini form no alcohol appreciable by analysis, but if alcohol exists in the subjacent liquid the mycoderma reduces it to water and carbonic acid gas by the fixation of the oxygen in the air.” Pasteur, having submerged the mycoderma and studied it to see how it would accommodate itself to the new conditions offered to it, and whether it would die like an animal asphyxiated by the sudden deprivation of oxygen, saw that life was continued in the submerged cells, slow, difficult, of a short duration, but undoubtedly life, and that this life was accompanied by alcoholic fermentation. This time fermentation was due to the fungus itself. The mycoderma, originally an aërobia—that is, a being to the life and development of which air was necessary—became, after being submerged, an anaërobia, that is, a creature living without air in the depths of the liquid, and behaving after the manner of ferments.

This extended the notions on aërobiæ and anaërobiæ which Pasteur had formerly discovered whilst making researches concerning the vibrio which is the butyric ferment, and those vibriones which are entrusted with the special fermentation known as putrefaction. Between the aërobiæ who require air to live and the anaërobiæ which perish when exposed to air, there was a class of organisms capable of living for a time outside the influence of air. No one had thought of studying the mouldiness which develops so easily when in contact with air; Pasteur was curious to see what became of it when submitted like the mycoderma to that unexpected régime. He saw the penicillium, the aspergillus, the mucor-mucedo take the character of ferments when living without air, or with a quantity of air too small to surround their organs as completely as was necessary to their aërobia-plant life. The mucor, when submerged and thus forced to become an anaërobia, offers budding cells, and there again it seemed as if they were yeast globules. “But,” said Pasteur, “this change of form merely corresponds to a change of function, it is but a self-adaptation to the new life of an anaërobia.” And then, generalizing again and seeking for laws under the accumulation of isolated facts, he thought it probable that ferments had, “but in a higher degree, a character common to most mucors if not to all, and probably possessed more or less by all living cells, viz., to be alternately aërobic or anaërobic, according to conditions of environment.”

Fermentation, therefore, no longer appeared as an isolated and mysterious act; it was a general phenomenon, subordinate however to the small number of substances capable of a decomposition accompanied by a production of heat and of being used for the alimentation of inferior beings outside the presence and action of air. Pasteur put the whole theory into this concise formula, “Fermentation is life without air.”

“It will be seen,” wrote M. Duclaux, “to what heights he had raised the debate; by changing the mode of interpretation of known facts he brought out a new theory.”

But this new theory raised a chorus of controversy. Pasteur held to his proofs; he recalled what he had published concerning the typical ferment, the yeast of beer, an article inserted in the reports of the Académie des Sciences for 1861, and entitled, The Influence of Oxygen on the Development of Yeast and on Alcoholic Fermentation. In this article Pasteur, à propos of the chemical action connected with vegetable life, explained in the most interesting manner the two modes of life of the yeast of beer.

1. The yeast, placed in some sweet liquid in contact with air, assimilates oxygen gas and develops abundantly; under those conditions, it practically works for itself only, the production of alcohol is insignificant, and the proportion between the weight of sugar absorbed and that of the yeast is infinitesimal. 2. But, in its second mode of life, if yeast is made to act upon sugar without the action of atmospheric air, it can no longer freely assimilate oxygen gas, and is reduced to abstracting oxygen from the fermentescible matter.

“It seems therefore natural,” wrote Pasteur, “to admit that when yeast is a ferment, acting out of the reach of atmospheric air, it takes oxygen from sugar, that being the origin of its fermentative character.” It is possible to put the fermentative power of yeast through divers degrees of intensity by introducing free oxygen in variable quantities.

After comparing the yeast of beer to an ordinary plant, Pasteur added that “the analogy would be complete if ordinary plants had an affinity for oxygen so strong as to breathe, by withdrawing that element from unstable components, in which case they would act as ferments on those substances.” He suggested that it might be possible to meet with conditions which would allow certain inferior plants to live away from atmospheric air in the presence of sugar, and to provoke fermentation of that substance after the manner of beer yeast.

He was already at that time scattering germs of ideas, with the intention of taking them up later on and experimenting on them, or, if time should fail him, willingly offering them to any attentive scientist. These studies on beer had brought him back to his former studies, to his great delight.

“What a sacrifice I made for you,” he could not help saying to Dumas, with a mixture of affection and deference, and some modesty, for he apparently forgot the immense service rendered to sericiculture, “when I gave up my studies on ferments for five whole years in order to study silkworms!!!”

No doubt a great deal of time was also wasted by the endless discussions entered into by his scientific adversaries; but those discussions certainly brought out and evidenced many guiding facts which are now undisputed, as for instance the following—1. Ferments are living beings. 2. There is a special ferment corresponding to each kind of fermentation. 3. Ferments are not born spontaneously.

Liebig and his partisans had looked upon fermentation as a phenomenon of death; they had thought that beer yeast, and in general all animal and vegetable matter in a state of putrefaction, extended to other bodies its own state of decomposition.

Pasteur, on the contrary, had seen in fermentation a phenomenon correlative with life; he had provoked the complete fermentation of a sweet liquid which contained mineral substances only, by introducing into it a trace of yeast, which, instead of dying, lived, flourished and developed.

To those who, believing in spontaneous generation, saw in fermentations but a question of chance, Pasteur by a series of experimental proofs had shown the origin of their delusion by indicating the door open to germs coming from outside. He had moreover taught the method of pure cultures. Finally, in those recent renewals of old quarrels on the transformations into each other of microscopic species, Pasteur, obliged by the mycoderma vini to study closely its alleged transformation, which he had himself believed possible, had thrown ample light on the only dark spot of his luminous domain.

“It is enough to think,” writes M. Duclaux concerning that long discussion, “we have but to remember that those who denied the specific nature of the germ would now deny the specific nature of disease, in order to understand the darkness in which such opinions would have confined microbian pathology; it was therefore important that they should be uprooted from every mind.”