Here, again, the disease is produced by a microscopic organism. A veterinary surgeon of Alsace, M. Moritz by name, was the first who suspected the presence of microbes in this disease; a veterinary surgeon of Turin, M. Peroncito, depicted it in 1878; a professor of the veterinary school of Toulouse, M. Toussaint, recognised it, in his turn, in 1879, and sent to Pasteur the head of a cock which had died of the cholera. But, however skilful they were, these observers had not succeeded in deciding the question of parasitism. None of them had hit upon a suitable cultivating medium for the parasite, nor had they reared it in successive crops. This, however, is the only method of proving that the virulence belongs exclusively to a parasite. It is absolutely necessary, in the study of maladies caused by microscopic organisms, to procure a liquid where the infectious parasite can grow and multiply without possible mixture of other organisms of different kinds. An infusion of the muscles of the fowl, neutralised by potash, and rendered sterile by a temperature of 110 to 115 degrees, has proved to be wonderfully appropriate to the culture of the microbe of fowl cholera. The facility of its multiplication in this medium is almost miraculous. In some hours the clearest infusion begins to grow turbid, and is found to be filled with a multitude of little organisms of an extreme tenuity slightly strangulated at their centres. These organisms have no movement of their own. In some days they change into a multitude of isolated specks, so diminished in volume that the liquid, which had been turbid to the extent of resembling milk, becomes again almost as clear as at first. The microbe here described belongs to a totally different group from that of the vibrios. It is ranged under the genus called 'micrococci.' 'It is in this group,' said Pasteur on one occasion, 'that the microbes of the viruses which are yet unknown will probably be one day found.'