When he returned to Paris, he met Sainte Claire Deville, who had come back from a scientific mission in Germany, and who had for the first time lost his brightness and optimism. The war appeared to him absolutely disastrous. He had seen the Prussian army, redoubtable in its skilful organization, closing along the frontier; the invasion was certain, and there was nothing to stay it. Everything was lacking in France, even in arsenals like Strasburg. At Toul, on the second line of fortifications, so little attention was paid to defence that the Government had thought that the place could be used as a dépôt for the infantry and cavalry reserves, who could await there the order for crossing the Rhine. “Ah! my lads, my poor lads!” said Sainte Claire Deville to his Ecole Normale students, “it is all up with us!” And he was seen, between two experiments, wiping his eyes with the comer of his laboratory apron. The students, with the ordinary confidence of youth, could not believe that an invasion should be so imminent. However, in spite of the privilege which frees _Normaliens_ from any military service in exchange for a ten years’ engagement at the University, they put patriotic duty above any future University appointments, and entered the ranks as private soldiers. Those who had been favoured by being immediately incorporated in a battalion of _chasseurs à pied_ the dépôt of which was at Vincennes, spent their last evening--their vigil as they called it--in the drawing-room of the sub-director of the Ecole, Bertin. Sainte Claire Deville and Pasteur were there, also Duruy, whose three sons had enlisted. Pasteur’s son, aged eighteen, was also on the eve of his departure. Every one of the students at the Ecole Normale enlisted, some as _chasseurs à pied_, some in a line regiment, others with the marines, in the artillery, even with the _franc tireurs_. Pasteur wished to be enrolled in the _garde nationale_ with Duruy and Bertin, but he had to be reminded that a half-paralysed man was unfit for service. After the departure of all the students, the Ecole Normale fell into the silence of deserted houses. M. Bouillier, the director, and Bertin decided to turn it into an ambulance, a sort of home for the _Normaliens_ who were stationed in various quarters of Paris. Pasteur, unable to serve his country except by his scientific researches, had the firm intention of continuing his work; but he was overwhelmed by the reverses which fell upon France, the idea of the bloodshed and of his invaded country oppressed him like a monomania. “Do not stay in Paris,” Bertin said to him, echoed by Dr. Godélier. “You have no right to stay; you would be a useless mouth during the siege,” he added, almost cheerfully, earnestly desiring to see his friend out of harm’s way. Pasteur allowed himself to be persuaded, and started for Arbois on September 5, his heart aching for the sorrows of France.