ni PASTEUE AND HYDROPHOBIA 171 



has not varied, even although the theory has been 

 modified profoundly. 



" At the present moment M. Pasteur believes that 

 his desiccated medullas contain a virus, not attenuated 

 or altered in character, but diminished in quantity, 

 and that it is less abundant in proportion as the 

 medullas have been long kept. He considers that 

 this virus will require a longer time to produce hydro- 

 phobia than would a fresh medulla, because the dura- 

 tion of incubation is ceteris paribus proportional to 

 the quantity of the virus. He supposes that during 

 this long incubation there is an advantage in that the 

 vaccinal effect — immunity — has time to produce itself, 

 but he explicitly states that this immunity is not due 

 to the virus. It is, he says, produced by a vaccinat- 

 ing substance which exists in the medulla side by side 

 with the virus, and that desiccation, whilst destroying 

 the virus (toxin), leaves the vaccinating matter (vaccin) 

 intact. 



'* Consequently the virus has nothing to do with 

 the result ; in the anti-rabic vaccination there is only 

 one thing of any service, and that is the vaccinal 

 matter. That being so, why choose an intensified 

 virus, a virus of short incubation ? Why make suc- 

 cessive inoculations with medullas of increasing viru- 

 lence ? Why not limit oneself to a medulla of fourteen 

 days' desiccation — a medulla which has ceased to be 

 virulent, and is still vaccinal, which contains what is 

 useful and nothing which is risky or dangerous ? " 



To these questions M. Bouchard replies that, prob- 

 ably because the present system has been found 



