“That aimlessness of criticism seems explicable to me, however, by this circumstance--that Medicine and Surgery are, I think, going through a crisis, a transition. There are two opposite currents, that of the old and that of the new-born doctrine; the first, still followed by innumerable partisans, rests on the belief in the spontaneity of transmissible diseases; the second is the theory of germs, of the living contagium with all its legitimate consequences....” The better to point out that difference between epochs, Pasteur respectfully advised M. Bouillaud, who was taking part in the discussion, to read over Littré’s _Medicine and Physicians_, and to compare with present ideas the chapter on epidemics written in 1836, four years after the cholera which had spread terror over Paris and over France. “Poisons and venoms die out on the spot after working the evil which is special to them,” wrote Littré, “and are not reproduced in the body of the victim, but virus and miasmata are reproduced and propagated. Nothing is more obscure to physiologists than those mysterious combinations of organic elements; but there lies the dark room of sickness and of death which we must try to open.” “Among epidemic diseases,” said Littré in another passage equally noted by Pasteur, “some occupy the world and decimate nearly all parts of it, others are limited to more or less wide areas. The origin of the latter may be sought either in local circumstances of dampness, of marshy ground, of decomposing animal or vegetable matter, or in the changes which take place in men’s mode of life.” “If I had to defend the novelty of the ideas introduced into medicine by my labours of the last twenty years,” wrote Pasteur from Arbois in September, 1879, “I should invoke the significant spirit of Littré’s words. Such was then the state of Science in 1836, and those ideas on the etiology of great epidemics were those of one of the most advanced and penetrating minds of the time. I would observe, contrarily to Littré’s opinion, that nothing proves the spontaneity of great epidemics! As we have lately seen the phylloxera, imported from America, invade Europe, so it might be that the causes of great pests were originated, unknowingly to stricken countries, in other countries which had had fortuitous contact with the latter. Imagine a microscopic being, inhabiting some part of Africa and existing on plants, on animals, or even on men, and capable of communicating a disease to the white race; if brought to Europe by some fortuitous circumstance, it may become the occasion of an epidemic....”