In presence of such facts it is easy to account for what takes place in the case of a bite from a mad dog. The circulation of the blood carries the virus to the surface of the brain, or to the surface of the spinal marrow; there it houses itself in particular spots, and, little by little, invades the nervous matter. This last would be progressively attacked throughout, if death from the medulla oblongata did not almost always supervene before the propagation of the virus can become general. The saliva glands are often rabic, doubtless because the virus oozes into them, little by little, from the nerves which enter these glands. Thus may the presence of this virus be explained in the saliva of mad dogs, where, at all times since the disease was first known, it has been found to exist. When the first point attacked by the virus is the spinal marrow, or certain portions of it, a general paralysis often precedes death. In this case the howling and biting symptoms are for the most part absent, and the dog continues to be caressing until it dies. In a thesis written by M. Roux, Pasteur's laboratory assistant, last July, we read the following:--'If we examine with care a little of the pulp taken freshly from the brain of a rabid animal, and compare it with the same substance from the brain of a healthy animal, it is difficult to distinguish any difference between the two. In the rabic pulp, however, besides the granulations which are found in profusion in the healthy pulp, there seem to exist little grains of extreme minuteness, almost imperceptible even with the strongest microscopes. In the cephalo-rachidic liquid so limpid in appearance, it is possible with great attention to detect similar little grains. Can this be the microbe of hydrophobia? Some do not hesitate to affirm that it is. For ourselves, as long as the cultivation of the microbe outside of the organism has not been effected, and that hydrophobia has not been communicated by means of artificial cultures, we shall abstain from expressing a definite opinion on the subject.' But the grand problem in regard to hydrophobia is, not so much the isolation of the microbe, as the finding of a means of preventing this frightful disease. * * * * *