Pasteur asked to be judged by the Academy. 'A commission alone,' said he, 'will terminate the debate.' The commission was named, and the position on both sides was clearly stated.
'I affirm,' said Pasteur, 'that everywhere it is possible to take from the midst of the atmosphere a certain quantity of air which contains neither egg nor spore, and which does not produce organisms in putrescible solutions.'
On his side, M. Joly wrote: 'If one alone of your bulbs remains unaltered we shall loyally acknowledge our defeat.' Lastly, M. Pouchet, as distinct and positive as M. Pasteur, said: 'I affirm that in whatever place I take a cubic decimeter of air, when this air is placed in contact with a fermentable liquid enclosed in a glass vessel hermetically sealed, the liquid will become filled with living organisms.'
This double declaration, which excited at that time all the learned world, took place in the month of January, 1864. Eager to engage in the combat, Pasteur waited impatiently for the order of the Commission that this experiment, which was to decide everything, should be made. But M. Pouchet begged for a postponement, desiring, he said, to wait for the warm season. Pasteur was astonished, but resigned himself to the delay. The Commission and the opponents met on June 15.
The Commission announced, 'that, as the whole dispute turned upon one simple fact, one single experiment ought to be undertaken, which alone would close the discussion.'
The partisans of spontaneous generation wished nevertheless to go through the entire series of their experiments. In vain the Commission tried to persuade them that this would make the judgment as long as the discussion itself had been, that all bore upon one fact, and that this fact could be decided by a single experiment. The heterogenists would not listen to this. M. Pouchet and M. Joly withdrew from the contest.
M. Jamin, an exact and authorised historian of these debates, observed that 'the heterogenists, however they may have covered their retreat, were thereby self-condemned. If they had been sure of the fact—which they were solemnly engaged to prove, under penalty of acknowledging themselves defeated—they would have hastened to demonstrate it, for it would have been the triumph of their doctrine. People do not allow themselves to be condemned by default except in causes in which they have no confidence.'