RABIES 535 



flasks plugged with cotton stoppers, and containing a quantity of some 

 hygroscopic material, such as caustic potash; and the whole was kept 

 at a temperature of about 22 (\ The cord when taken out at the end 

 of the first twenty-four hours was found to be almost as active as the 

 fresh untreated cord; that removed at the end of forty-eight hours wa^ 

 slightly less active than that removed twenty-four hours previously; 

 and the diminution in virulence, though gradual, progressed regularly 

 and surely until, as already noted, at the end of the fourteenth or fif- 

 teenth day the virus was inactive. An emulsion of the cord of the last 

 day was made, and a certain quantify injected into a dog that had been 

 bitten; this was followed by an injection of an emulsion of a thirteenth- 

 day cord, and so on until the animal had been injected with a perfectly 

 fresh and, therefore, extremely active cord, corresponding to the fixed 

 virus. Animals treated in this way were now found to be absolutely 

 protected, even against subdural inoculation with considerable quantities 

 of the most virulent virus; and thus Pasteur's protective inoculation 

 against rabies became an accomplished fact. As it would be impossible, 

 however, or very undesirable, to inject any but persons who had actually 

 been bitten by a rabid, or presumably rabid, animal, Pasteur continued 

 his experiments, in order to see whether it would not be possible to 

 cure a patient already bitten. He carried on, therefore, a series of 

 experiments which led to the discovery that if the process of inoculation 

 be begun within five days of the bite in animals in which the incubation 

 period was at least fourteen days, almost every animal bitten can be 

 saved ; and that even if the treatment be commenced at a longer interval 

 after the bite a certain proportion of recoveries can be obtained. Thus 

 the application of this method of treatment to the human subject was 

 not tried until it had been proved in animals that such protection could 

 be obtained, and that such protection would last for at least two years, 

 and probably longer. 



The chance of success in the human subject appears to be even 

 greater than in the dog or rabbit, seeing that on account of the resist- 

 ance offered by the human tissues to the virus the period of incubation 

 is comparatively prolonged; very rarely, if ever, does an outbreak of the 

 disease in man occur before an interval of at least fifteen days. The 

 first symptoms usually appear in the fifth or sixth week, sometimes not 

 until the third month; exceptionally the incubation period has lasted 

 for a year. Thus there is an opportunity of obtaining immunity by 

 beginning the process of vaccination soon after the bite has been inflicted, 

 the protection being complete before the incubation period has passed. 

 In his earlier experiments Pasteur injected on each succeeding day 

 emulsions from a cord dried for one day less until cords dried five days 

 were reached; but later he used those dried for only three days. This 

 was the "simple" ten-day method. It was soon evident that although 

 this method was efficacious where the wounds were not severe, and 

 were confined to parts in which the nerve supply was not extensively 

 interfered with, it was often quite inadequate in serious cases, as of 

 wounds about the face, or of wounds inflicted by a mad wolf, the virus 



