580 HYDROPHOBIA 



of the infliction of a rabic wound prevents the disease from 

 developing, and that if done within half an hour it saves a 

 proportion of the cases. After this time, cauterisation only 

 lengthens the period of incubation ; but, as we shall see 

 presently, this is an extremely important effect. 



The work of Pasteur has, however, revolutionised the whole 

 treatment of wounds inflicted by hydrophobic animals. Pasteur 

 started with the idea that, since the period of incubation in the 

 case of animals infected subdurally from the nervous systems of 

 mad dogs is constant in the dog, the virus has been from time 

 immemorial of constant strength. Such a virus, of what might 

 be called natural strength, is usually referred to in his works as 

 the virus of la rage des rues, 1 in the writings of German authors 

 as the virus of die Strasswuth. 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 inoculation 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, constancy of strength being in- 

 dicated by the unvarying recurrence of paresis on the sixth day. 

 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 



1 While Pasteur's original statements regarding the constancy of the 

 virulence of the street-virus were probably accurate for the street dogs of 

 Paris, it has been found that if the general virulence of virus derived from 

 animals in nature be studied, considerable variation occurs. It is now 

 usual to apply the term street- virus to any virus derived from an animal 

 becoming rabid under natural conditions of infection. 



