512 APPENDIX B. 



exposure at 50" C. Again, its potency probably varies in nature accord- 

 ing to tlie source. Thus, while the death-rate among persons bitten by 

 mad dogs is about 16 per cent, the corresponding death-rate after the 

 bites of wolves is 80 per cent. Here, however, it must be kept in view 

 that, as the wolf is naturally the more savage animal, the number and 

 extent of the bites, i.e. the number of channels of entrance of the virus 

 into the body, and the total dose, are greater than in the case of persons 

 bitten by dogs. As we shall see, alterations in the potency of the virus 

 can certainly be effected by artificial means. 



The Prophylactic Treatment of Hydrophobia. — Until the publica- 

 tion of Pasteur's researches in 1885, the only means adopted to prevent 

 the development of hydrophobia in a person bitten by a rabid animal, 

 had consisted in the cauterisation of the wound. Such a procedure was 

 undoubtedly not without effect. It has been shown that cauterisation 

 within five minutes of the infliction of a rabic wound prevents the disease 

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

 tion 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 treat- 

 ment of wounds inflicted by hydrophobic animals. Pasteur started with 

 the idea that, since the period of incubation in the case of animals in- 

 fected 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, in the writings of Ger- 

 man authors as the virus of die Strasswuth. Pasteur found on inoculat- 

 ing 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 gradu- 

 ally lost its virulence, as evidenced by lengthened periods of incubation 

 on subdural inoculation of dogs, until it wholly lost the power of pro- 

 ducing 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. subcuta- 

 neous 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 



