This programme left him no retreat. The Melun Agricultural Society put sixty sheep at Pasteur’s disposal; twenty-five were to be vaccinated by two inoculations, at twelve or fifteen days’ interval, with some attenuated charbon virus. Some days later those twenty-five and also twenty-five others would be inoculated with some very virulent charbon culture.
“The twenty-five unvaccinated sheep will all perish,” wrote Pasteur, “the twenty-five vaccinated ones will survive.” They would afterwards be compared with the ten sheep which had undergone no treatment at all. It would thus be seen that vaccination did not prevent sheep from returning to their normal state of health after a certain time.
Then came other prescriptions, for instance, the burying of the dead sheep in distinct graves, near each other and enclosed within a paling.
“In May, 1882,” added Pasteur, “twenty new sheep, that is, sheep never before used for experimentation, will be shut within that paling.”
And he predicted that the following year, 1882, out of those twenty-five sheep fed on the grass of that little enclosure or on forage deposited there, several would become infected by the charbon germs brought to the surface by earthworms, and that they would die of splenic fever. Finally, twenty-five other sheep might be folded in a neighbouring spot, where no charbon victims had ever been buried, and under these conditions none would contract the disease.
M. de la Rochette having expressed a desire that cows should be included in the programme, Pasteur answered that he was willing to try that new experiment, though his tests on vaccine for cows were not as advanced as those on sheep vaccine. Perhaps, he said, the results may not be as positive, though he thought they probably would be. He was offered ten cows; six were to be vaccinated and four not vaccinated. The experiments were to begin on the Thursday, 5th May, and would in all likelihood terminate about the first fortnight in June.
At the time when M. Rossignol declared that all was ready for the fixed time, an editor’s notice in the Veterinary Press said that the laboratory experiments were about to be repeated in campo, and that Pasteur could thus “demonstrate that he had not been mistaken when he affirmed before the astonished Academy that he had discovered the vaccine of splenic fever, a preventative to one of the most terrible diseases with which animals and even men could be attacked.” This notice ended thus, with an unexpected classical reminiscence: “These experiments are solemn ones, and they will become memorable if, as M. Pasteur asserts, with such confidence, they confirm all those he has already instituted. We ardently wish that M. Pasteur may succeed and remain the victor in a tournament which has now lasted long enough. If he succeeds, he will have endowed his country with a great benefit, and his adversaries should, as in the days of antiquity, wreathe their brows with laurel leaves and prepare to follow, chained and prostrate, the chariot of the immortal Victor. But he must succeed: such is the price of triumph. Let M. Pasteur not forget that the Tarpeian Rock is near the Capitol.”
On May 5 a numerous crowd arriving from Melun station or from the little station of Cesson, was seen moving towards the yard of Pouilly le Fort farm; it looked like a mobilisation of Conseillers Généraux, agricultors, physicians, apothecaries, and especially veterinary surgeons. Most of these last were full of scepticism—as was remarked by M. Thierry, who represented the Veterinary Society of the Yonne, and one of his colleagues, M. Biot, of Pont-sur-Yonne. They were exchanging jokes and looks to the complete satisfaction of Pasteur’s adversaries. They were looking forward to the last and most virulent inoculation.
Pasteur, assisted not only by Messrs. Chamberland and Roux, but also by a third pupil of the name of Thuillier, proceeded to the arrangement of the subjects. At the last moment, two goats were substituted for two of the sheep.
Vaccination candidates and unvaccinated test sheep were divided under a large shed. For the injection of the vaccinal liquid, Pravaz’s little syringe was used; those who have experienced morphia injections know how easily the needle penetrates the subcutaneous tissues. Each of the twenty-five sheep received, on the inner surface of the right thigh, five drops of the bacteridian culture which Pasteur called the first vaccine. Five cows and one ox substituted for the sixth cow were vaccinated in their turn, behind the shoulder. The ox and the cows were marked on the right horn, and the sheep on the ear.