The idea then occurred to Pasteur and his assistants, to inoculate the virulent rabic matter in its pure state under the _dura mater_ on the surface of the brain of a dog. Why not carry the virus, said Pasteur, directly to the place of its activity and development? After having trepanned the skull of a chloroformed dog, a little bit of the medulla of an animal which had died of hydrophobia was deposited on the surface of the brain. As soon as the influence of the chloroform was dissipated, the dog recovered its healthy appearance. It ate its food that same evening. But after some days the symptoms of hydrophobia appeared. The animal became dejected and restless; it tossed its litter about, refused all nourishment. A doleful, sharp howling was the first indication of the rabic voice, which is but one long cry of suffering and appeal, mingled with barkings from hallucinations. The stomach became depraved; the dog swallowed hay and straw. It soon grew furious, agitated with violent convulsions; finally, after a last fit, it died. During all this time there was great rejoicing in the laboratory. They were at last in possession of a method for singularly shortening the period of incubation, and for communicating the disease with certainty. The experiments were multiplied; all the dogs which were trepanned, and which received on the surface of the brain a little of the medulla of the rabid animal, succumbed to the disease, with very rare exceptions, within a period of twenty days. Did not the method pursued demonstrate, among other things, that hydrophobia is a disease of the brain; that the seat of the rabic virus, far from being exclusively in the saliva, belongs, above all, to the cerebral matter? Other results, in addition to this one, were not slow in revealing themselves. It was established that not only the brain, but the spinal marrow, along its whole length, may be rabic, and that the nerves themselves throughout their whole system, from the centre to the periphery, may contain the virus of hydrophobia. If there exists a microbe of hydrophobia, its medium of cultivation in the body is, _par excellence_, the brain, the spinal marrow, and the nerves. It was also established that there were localisations of virus in certain parts of the mucous system, and that the very considerable differences of rabic symptoms which exist in different cases of hydrophobia, must be sought for in this fact. At the moment of death the medulla oblongata is always rabic. Finally, it was established that hydrophobia could be given (and almost as rapidly as by trepanning) by inoculating rabic nervous matter into the circulation of the blood by a vein.