1884—1885 395 



artificial medium, let us try the brain of living rabbits; it 

 would indeed be an experimental feat ! ' ' 



As soon as a trephined and inoculated rabbit died paralyzed, 

 a little of his rabic medulla was inoculated to another; each 

 inoculation succeeded another, and the time of incubation be- 

 came shorter and shorter, until, after a hundred uninterrupted 

 inoculations, it came to be reduced to seven days. But the 

 virus, having reached this degree, the virulence of which was 

 found to be greater than that of the virus of dogs made rabid 

 by an accidental bite, now became fixed; Pasteur had mastered 

 it. He could now predict the exact time when death should 

 occur in each of the inoculated animals; his predictions were 

 verified with surprising accuracy. 



Pasteur was not yet satisfied with the immense progress 

 marked by infallible inoculation and the shortened incubation; 

 he now wished to decrease the degrees of virulence — when the 

 attenuation of the virus was once conquered, it might be hoped 

 that dogs could be made refractory to rabies. Pasteur abstracted 

 a fragment of the medulla from a rabbit which had just died of 

 rabies after an inoculation of the fixed virus; this fragment 

 was suspended by a thread in a sterilized phial, the air in which 

 was kept dry by some pieces of caustic potash lying at the bottom 

 of the vessel and which was closed by a cotton-wool plug to pre- 

 vent the entrance of atmospheric dusts. The temperature of 

 the room where this desiccation took place was maintained at 

 23° C. As the medulla gradually became dry, its virulence 

 decreased, until, at the end of fourteen days, it had become 

 absolutely extinguished. This now inactive medulla was 

 crushed and mixed with pure water, and injected under the 

 skin of some dogs. The next day they were inoculated with 

 medulla which had been desiccating for thirteen days, and so 

 on, using increased virulence until the medulla was used of a 

 rabbit dead the same day. These dogs might now be bitten by 

 rabid dogs given them as companions for a few minutes, or 

 submitted to the intracranial inoculations of the deadly virus; 

 they resisted both. 



Having at last obtained this refractory condition, Pasteur was 

 anxious that his results should be verified by a Commission. 

 The Minister of Public Instruction acceded to this desire, and 

 a Commission was constituted in May, 1884, composed of 

 ^Messrs. Beclard, Dean of the Faculty of Medicine, Paul Bert, 

 Bouley, Yillemin. Vulpian, and Tisserand, Director of the 



