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.'