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paper are carefully considered, it would seem fhat we could 

 not expect to- see any Bacillus anthracis in such cases. 



1.326. Principle of Inoculation. Pathogenic or disease 

 producing organisms subjected to certain conditions, either 

 diminish or augment in their virulence. The virus of 

 swine plague inoculated in pigeons increases in virulence 

 at each successive generation of its passage through pigeons. 

 If, however, this virus is passed through successive genera- 

 tions in the bodies of rabbits, it becomes gradually at- 

 tenuated in virulence, and after the tenth generation the 

 virus taken from the rabbit may be used for inoculating pigs 

 to protect them against swine-plague. 



1.327. Similarly the virus of rabies passing through the 

 bodies of monkeys becomes sufficiently attenuated after the 

 tenth generation for the virus from the tenth monkey being 

 used for inoculating dogs to protect them from rabies. Pas- 

 sing, however, through the bodies of rabbits, the virus of 

 rabies augments in virulence. A rabbit inoculated with the 

 virus of rabies from a mad dog dies in 18 to 20 days. A 

 second rabbit inoculated with the virus taken from this dead 

 rabbit will take less time to die, and so on, until the 3oth 

 rabbit inoculated with the virus from the 2gth rabbit takes 

 only six days to die. Here, however, the maximum of virul- 

 ence is reached ; the 31 st, 32nd, 33rd, &c., do not die any 

 quicker than the 3oth rabbit, but they all take after the 3oth 

 rabbit six days to die. 



1.328. But the conditions under which pathogenic organ- 

 isms change their character are various. Some of these have 

 been discovered, and they are made use of in attenuating the 

 virulence of the virus, and introducing the attenuated virus 

 into the bodies of the animals to protect them from accidental 

 inoculation or infection with the virulent virus. The usual 

 methods adopted are heat and drying. Heat is applied in 

 attenuating anthrax vaccine, heat and desiccation both in 

 attenuating charbon vaccine, and desiccation in attenuating 



