LOUIS PASTEUR 307 



tremity of the spinal cord, and only after a time reach the brain. 

 It may be met with at one or at several points of the encephalon whilst 

 being absent at certain other points of the same region. 



If an animal is killed whilst in the power of rabies, it may require 

 a pretty long search to discover the presence here or there in the 

 nervous system, or in the glands, of the virus of rabies. We have 

 been fortunate enough to ascertain that in all cases, when death has 

 been allowed to supervene naturally, the swelled-out portion, or bulb, 

 of the medulla oblongata nearest to the brain, and uniting the spinal 

 cord with it, is always rabid. When an animal has died of rabies 

 (and the disease always ends in death), rabid matter can with cer- 

 tainty be obtained from its bulb, capable of reproducing the disease 

 in other animals when inoculated into them, after trephining, in the 

 arachnoid space of the cerebral meninges. 



Any street dog whatsoever, inoculated in the manner described 

 with portions of the bulb of an animal which has died of rabies, will 

 certainly develop the same disease. We have thus inoculated several 

 hundreds of dogs brought without any choice from the pound. Never 

 once was the inoculation a failure. Similarly also, with uniform suc- 

 cess, several hundred guinea-pigs, and rabbits more numerous still. 



Those two great results, the constant presence of the virus in the 

 bulb at the time of death, and the certainty of the reproduction of the 

 disease by inoculation into the arachnoid space, stand out like experi- 

 mental axioms, and their importance is paramount. Thanks to the 

 precision of their application, and to the well-known daily repetition of 

 those two criteria of our experiments, we have been able to move for- 

 ward steadily and surely in that arduous study. But, however solid 

 those experimental bases, they were, nevertheless, incapable in them- 

 selves of giving us the faintest notion as to some method of vaccina- 

 tion against rabies. In the present state of science the discovery of a 

 method of vaccination against some virulent malady presupposes : 



1. That we have to deal with a virus capable of assuming diverse 

 intensities, of which the weaker ones can be put to vaccinal or pro- 

 tective uses. 



2. That we are in possession of a method enabling us to reproduce 

 those diverse degrees of virulence at will. 



At the present time, however, science is acquainted with one sort 

 of rabies only — viz., dog rabies. 



