“A remarkable thing is that the bacteridia whose virulence has been attenuated may afterwards be cultivated in a temperature of 30° C. to 35° C., at which temperature they give germs presenting the same virulence as the filaments which formed them.” Bouley, who was a witness of all these facts, said, in other words, that “if that attenuated and degenerated bacteridium is translated to a culture medium in a lower temperature, favourable to its activity, it becomes once again apt to produce spores. But those spores born of weakened bacteridia, will only produce bacteridia likewise weakened in their swarming faculties.” Thus is obtained and enclosed in inalterable spores a vaccine ready to be sent to every part of the world to preserve animals by vaccination against splenic fever. On the day when he became sure of this discovery, Pasteur, returning to his rooms from his laboratory, said to his family, with a deep emotion--“Nothing would have consoled me if this discovery, which my collaborators and I have made, had not been a French discovery.” He desired to wait a little longer before proclaiming it. Yet the cause of the evil was revealed, the mode of propagation indicated, prophylaxis made easy; surely, enough had been achieved to move attentive minds to enthusiasm and to deserve the gratitude of sheep owners! So thought the _Society of French Agricultors_, when it decided, on February 21, 1881, to offer to Pasteur a medal of honour. J. B. Dumas, detained at the Académie des Sciences, was unable to attend the meeting. He wrote to Bouley, who had been requested to enumerate Pasteur’s principal discoveries at that large meeting--“I had desired to make public by my presence my heartfelt concurrence in your admiration for him who will never be honoured to the full measure of his merits, of his services and of his passionate devotion to truth and to our country.” On the following Monday, Bouley said to Dumas, as they were walking to the Académie des Sciences, “Your letter assures me of a small share of immortality.” “See,” answered Dumas, pointing to Pasteur, who was preceding them, “there is he who will lead us both to immortality.” On that Monday, February 28, Pasteur made his celebrated communication on the vaccine of splenic fever and the whole graduated scale of virulence. The secret of those returns to virulence lay entirely in some successive cultures through the body of certain animals. If a weakened bacteridium was inoculated into a guinea-pig a few days old it was harmless; but it killed a new-born guinea-pig.