_METHOD OF DISCUSSION AND CONTRADICTIONS._ Every new discovery produces a revolution in general ideas; a revolution gladly hailed by some, but opposed by others as disturbing their habits of thought and reasoning. Those also who are thrown out in their calculations, while engaged in working out a problem in any way similar to the one that has been solved, too often atone for their dilatoriness by furious denial of the newly asserted truth. The great fact of the attenuation of virus, the artificial production of the vaccines of chicken cholera and of splenic fever, the importance of their employment for the preservation of animals from these diseases, excited throughout the world a surprise and enthusiasm which passionate critics soon sought to disparage. The fiercest attack was from Germany. It commenced immediately after Pasteur's triumph at the International Congress of Medicine held in London in 1881. The German doctor Koch and his colleagues, MM. Gaffki and Lœffler, published in Berlin, in the report of the German Sanitary Office, a kind of scientific tirade against the discovery of virus vaccine, and the possibility of utilising it in the large operations of cattle-breeding. At the London Congress Dr. Koch had said to a French physician that the possibility of attenuating virus was a thing too good to be true. The whole question was therefore reopened by Dr. Koch and his disciples. At first Pasteur let the torrent flow; but, not being the man to give way before an adversary, he at last declared that the attacks of the German savants must be repelled at Berlin itself. Continual applications for splenic vaccine were made to him from different parts of Germany. M. Pasteur replied that, seeing that the discovery was so formally contested in Prussia, it would be well, before sending any vaccine abroad, to institute a great demonstrative experiment, as had been done at Pouilly-le-Fort.