Every new discovery produces a revolution in general ideas; a revolution gladly hailed by some, but opposed by others as disturbing their habits of thought and reasoning. Those also who are thrown out in their calculations, while engaged in working out a problem in any way similar to the one that has been solved, too often atone for their dilatoriness by furious denial of the newly asserted truth. The great fact of the attenuation of virus, the artificial production of the vaccines of chicken cholera and of splenic fever, the importance of their employment for the preservation of animals from these diseases, excited throughout the world a surprise and enthusiasm which passionate critics soon sought to disparage. The fiercest attack was from Germany. It commenced immediately after Pasteur's triumph at the International Congress of Medicine held in London in 1881. The German doctor Koch and his colleagues, MM. Gaffki and Loeffler, published in Berlin, in the report of the German Sanitary Office, a kind of scientific tirade against the discovery of virus vaccine, and the possibility of utilising it in the large operations of cattle-breeding.

At the London Congress Dr. Koch had said to a French physician that the possibility of attenuating virus was a thing too good to be true. The whole question was therefore reopened by Dr. Koch and his disciples. At first Pasteur let the torrent flow; but, not being the man to give way before an adversary, he at last declared that the attacks of the German savants must be repelled at Berlin itself. Continual applications for splenic vaccine were made to him from different parts of Germany. M. Pasteur replied that, seeing that the discovery was so formally contested in Prussia, it would be well, before sending any vaccine abroad, to institute a great demonstrative experiment, as had been done at Pouilly-le-Fort.

Dr. Roloff, head of the Veterinary School of Berlin, hastened to take the initiative, by an application to the German Minister of Agriculture. The minister at once nominated a Commission to follow the experiments in vaccination and to draw up a report for the German Government. M. Pasteur entrusted the conduct of the vaccinations to his new colleague, Louis Thuillier, who accepted with deep and silent joy the management of an experiment that was to test a French discovery. He was always ready for anything, this brave Thuillier, who was destined to die, a martyr to the cause of science, in the full promise of his youth, and in the full hope of glory. His courage and his work were alike great and silent. In the laboratory he would spend days, even weeks, without speaking, bent over his microscope with tenacious resolution, endeavouring to follow Pasteur in all his investigations: proud to live near his illustrious master, happy to be his disciple and to be loved by him almost as a son. What a vacancy he has left in the laboratory! What a place he might have held in science!

The composition of the German Commission, over which M. Beyer, member of the Superior Council of Government, presided, showed clearly the importance attached by Germany to the investigation of this French discovery. Among its members was the famous Professor Virchow.

The experiments were carried out on the estate of Pakisch. The minutes and reports of the Commission left no doubt as to the correctness of the facts announced by Pasteur. But, as the negations of Dr. Koch and his colleagues embraced questions beyond that of the prophylaxy of splenic fever, Pasteur did not rest content with this initial success; he sought for a fresh opportunity of convincing his opponents. This opportunity occurred in September 1882, when an International Hygienic Congress was held at Geneva. Thither went Pasteur, hoping to meet Dr. Koch at the sittings; and he was not disappointed. Dr. Koch was there, surrounded by his disciples. From the tribune of the Congress, Pasteur refuted his criticism, exposed his errors, and challenged him to a discussion in the presence of competent judges. There was an instantaneous salvo of applause, and everyone awaited Dr. Koch's reply. But he declined all debate, reserving his case for careful and deliberate statement in the press.

It took three months for Dr. Koch to bring out a small pamphlet, and these three months had borne their fruit. The discovery of the attenuation of virus, which had been so vehemently attacked only a year before in the report of the Sanitary Office, was now extolled by Dr. Koch as a discovery of the first importance. Being, however, unwilling absolutely to stultify himself, he continued the attack by denying its efficacy in practical agriculture.

The clear, direct style of argument, which goes straight to its point, was invariably adopted by Pasteur.

'Contradictions may retard, although they cannot ultimately prevent, the recognition of truth,' he once remarked to me when walking in the gardens of the École Normale; 'that is why it is so important to remove the obstacles which temporarily clog and hamper it. In scientific discussions, it is not as in politics,' he added with a smile, 'where demonstration is often difficult. In the natural sciences, doctrines must be based on an assemblage of results, of observations, and of experiments. If a doctrine is challenged, it seldom happens that its truth or falsehood cannot be established by the application of some crucial test. Even a single experiment will often suffice either to refute or consolidate the doctrine.'

Reviewing the labours of the past forty years, Pasteur then called to mind the numerous controversies in which he had been engaged. Not only had he been attacked by Pouchet and Joly on the question of spontaneous generation, by Liebig on the subject of fermentation, by Germans and Italians regarding the attenuation of virus, but every one of his assertions had been met with such passionate opposition that, from sheer weariness, he had invariably ended by referring the matter to some authorised commission, only asking it to put an end to all strife by coming to some definite decision.

The upshot was at times somewhat amusing. For instance, when Pasteur described to the Academy of Medicine how, simply by lowering the temperature of a hen, he had made her susceptible to inoculation with splenic fever, the facts were at once denied by M. Colin, a professor of the school of Alfort. Pasteur immediately requested that a commission might be named, which should include both himself and his opponent among its members. This was on a Tuesday, one of the Academy days of sitting. The following Saturday, in presence of the whole commission, Pasteur produced four hens that had died of splenic fever. M. Colin himself conducted the autopsy. It was clear to everyone that their blood was full of the filaments of the splenic fever parasite. The procÈs-verbal was drawn up and signed by all the members of the commission, necessarily including M. Colin. The following Tuesday it was read at the sitting of the Academy. To cover his retreat M. Colin now contended that the hens had taken splenic fever not because they had been subjected to a chilling process, but because, so as to keep them in the water, the poor creatures had had their wings and feet tied to planks. This sentimental objection was disposed of by comparative experiments that had been made on hens similarly tied and inoculated, but not chilled. The latter had in no case taken the disease.

At the Academy of Sciences, some days later, a mine was sprung upon Pasteur by a posthumous publication of Claude Bernard's. He again submitted this abruptly raised question to the decision of the Academy. A series of experiments had been found among Bernard's papers, having as their object the inauguration of a new method of spontaneously generating the substance which causes the fermentation of the must of the grape.

'I will start for the Jura,' said Pasteur. 'In the midst of my vineyard, which,' he proudly added, 'is ten meters square, I will cover over some stocks with an improvised frame. These stocks will go on living and bearing grapes, which will ripen. It is now July. At this time of year, as I have already declared, the germs of the cellules which form the ferment of the grape in the vats do not yet exist, either on the green grapes, on the bunches, or on the vine leaves. I will envelop the bunches of the stocks that are underneath the frame with a layer of cotton wool that has been raised to a temperature of 150 degrees Centigrade. This done, I will come back to Paris with the keys of the frame in my pocket, not returning to the Jura until the vintage season, at the beginning of October. I predict to the Academy, that the grapes wrapped in cotton wool under the frame, and which will have grown ripe, may be crushed in the open air, and that the juice coming from them will not be capable of fermentation.'

This prediction was fulfilled. In October, Pasteur returned to the Jura, plucked off several of these stocks, laden with ripe bunches, and brought them with the utmost care to Paris. He had at last the satisfaction of depositing them intact on the table of the Academy of Sciences. He then invited M. Berthelot (editor of Bernard's pamphlet), and all his colleagues, to cut off as many bunches as they pleased. 'Only crush them in contact with pure air,' said he, 'and I defy you to produce fermentation.'

How often was Pasteur obliged to return to facts already proved, not only at the Academy of Sciences, but at the Academy of Medicine, where M. Jules GuÉrin, at the age of eighty, challenged him to a duel as his scientific ultimatum! If M. Pasteur at times pleaded his cause with too much passion, it was the passion of truth, the burning desire to convince, which lent such power and defiance to his vibrating voice. He could not endure his work to be attacked—not from pride, none was more modest than he—but from irritation at the denial of positive facts; facts of which he was a thousand times assured, and which all the world might verify. No one now remembers these discussions. Time has passed, and opposition has been overthrown. It has been granted to Pasteur to see, everywhere around him, the beneficent results of his discoveries. From all parts, from his own as well as from foreign countries, such proofs of admiration and gratitude have been showered upon him as are usually granted only to those whose death has atoned for their genius. He has opened up such sources of wealth to industry and agriculture that, as the learned English professor Huxley has truly said, 'Pasteur's discoveries suffice, of themselves, to cover the war indemnity of five milliards of francs paid by France to Germany.' His investigations of contagious diseases have revealed immense possibilities in prophylaxy. But Pasteur considered these marvellous discoveries as a mere beginning. 'You will see,' he often said, 'how it will all grow by-and-by. Would that my time were longer!'