298 LOUIS PASTEUR. 



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 pre- 

 sence of this virus be explained in the saliva of mad 

 dogs, w r here, 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 pre- 

 cedes 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 labora- 

 tory 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 



