PROPHYLAXIS OF HYDROPHOBIA. 511 



strength, is usually referred to in his works as the virus of 

 la rage des rues, in the writings of German authors as the 

 virus of die Strassivuth. Pasteur found on inoculating a 

 monkey subdurally with such a virus, and then inoculating 

 a second monkey from the first, and so on with a series of 

 monkeys, that it gradually lost its virulence, as evidenced 

 by lengthened periods of incubation on subdural inocula- 

 tion of dogs, until it wholly lost the power of producing 

 rabies in dogs, when introduced subcutaneously. When 

 this point had been attained, its virulence was not 

 diminished by further passage through the monkey. On 

 the other hand, if the virus of la rage des rues were 

 similarly passed through a series of rabbits or guinea-pigs, 

 its virulence was increased till a constant strength (the virus 

 fixe) was attained. Pasteur had thus at command three 

 varieties of virus that of natural strength, that which had 

 been attenuated, and that which had been exalted. He 

 further found that, commencing with the subcutaneous 

 injection of a weak virus and following this up with the 

 injection of the stronger varieties, he could ultimately, in a 

 very short time, immunise dogs against subdural infection 

 with a virus which, under ordinary conditions, would 

 certainly have caused a fatal result. He also elucidated 

 the fact that the exalted virus contained in the spinal cords 

 of rabbits such as those referred to, could be attenuated so 

 as no longer to produce rabies in dogs by subcutaneous 

 injection. This was done by drying the cords in air over 

 caustic potash (to absorb the moisture), the diminution of 

 virulence being proportional to the length of time during 

 which the cords were kept. Accordingly, by taking a series 

 of such spinal cords kept for various periods of time, he 

 was supplied with a series of vaccines of different strengths. 

 Pasteur at once applied himself to find whether the com- 

 paratively long period of incubation in man could -not be 

 taken advantage of to " vaccinate " him against the disease 

 before its gravest manifestation took place. The following 

 is the record of the first case thus treated. The technique 

 was to rub up in a little sterile bouillon a small piece of 



