PREVENTIVE MEDICINE 297 



for at least 5 days after complete recovery. It is certain that by 

 no means every person bitten by a dog proved to have been rabid 

 subsequently develops symptoms. The same is true in the case of 

 animals in which probably not more than a half of those bitten by 

 rabid animals develop the disease (Hutyra and Marek). 



The virus in nervous tissue retains its virulence for months if 

 protected from desiccation and putrefaction (Pasteur). Fluid 

 saliva has been found to be infective even after 24 hours (Gibier). 

 The virus is destroyed at 52 to 58 C in 30 minutes (Hogyes). 

 The virus is resistant to cold and to putrefaction, e.g., Galtier found 

 the medulla of a dog that had been buried for 44 days to be still 

 virulent. The virus is also resistant to glycerine.* 



Starting with the observation that dogs can be artificially 

 immunised, Pasteur developed his well-known method of conferring 

 immunity upon persons who had been bitten by animals affected 

 with rabies. As above stated, the period of incubation in rabies 

 is, in general, a long one, and Pasteur's object was to immunise 

 the person during this period and so avert attack by the natural 

 virus. He found that on injecting rabbits subdurally with 

 natural or so-called " street " virus the period of incubation was 

 about 15 days, but that this could be reduced by passage from 

 rabbit to rabbit to about 6 or 7 days. This virus, which he called 

 the fixed virus of rabies, is exalted in virulence only for the rabbit 

 and only by subdural inoculation; for other animals, includ- 

 ing man, the fixed virus is attenuated. The fixed virus is present 

 in the spinal cord of the rabbit and this, after death, is cut out 

 and suspended in a bottle containing solid potash, which has the 

 effect of absorbing moisture from the air, and so leads to gradual 

 desiccation of the cord, which, in turn, leads to gradual loss of viru- 

 lence, so that by the fourteenth day the cord is no longer infective. 

 People who have been bitten by rabid animals are submitted at 

 Pasteur Institutes, as soon as possible after being bitten, to a course 

 of treatment consisting of subcutaneous inoculations at intervals 

 of a few days with rabbits' spinal cords of gradually increasing 

 virulence. The length of the course varies according to the posi- 

 tion and extent of the bites. If these are very numerous or situated 

 about the head, the person receives injections over a period of 3 

 weeks ; if the bites are not serious and are situated on the arms or 

 legs the course lasts about a fortnight. Large numbers of people 

 have received this treatment since its inception in 1885, and the 

 mortality among the second class (bites on arms or legs) was less 

 than 1 per cent. Among those bitten badly or about the head 

 * Hutyra and Marek, Spec. Path., Vol. I., p. 466. 



