52 BACTERIOLOGY. 



it was exposed to 47 C., was fatal to guinea-pigs; but after one 

 hour at 47 C. the virulence was diminished, and, though ultimately 

 fatal, life was prolonged ; after two hours' exposure at 47 C. only 

 half the animals died; and after three hours' exposure they 

 recovered, and were rendered refractory to subsequent inoculation. 



Attenuation of the virus of anthrax has also -been induced by 

 chemical means. Chamberland and Roux stated that a fresh growth 

 started from a cultivation of bacilli which had been subjected for 

 twenty- nine days to ^J^ of carbolic acid was found to be inert in 

 guinea-pigs and rabbits. Bichromate of potash added to a cultiva- 

 tion in the proportion of y^-g^- to ^^^ gave, after three days, a 

 new growth, which killed rabbits, guinea-pigs, and half the sheep 

 inoculated ; after ten days, rabbits and guinea-pigs, but not sheep ; 

 and after a longer time even guinea-pigs were unaffected. 



In other diseases similar results have been obtained. Arloing, 

 Cornevin, and Thomas found that by inoculating a small quantity 

 of the virus of symptomatic anthrax anywhere in the subcutaneous 

 connective tissue, or a moderate quantity at the root of the tail, 

 and even by intravenous injection, immunity was obtained from a 

 virulent dose. 



In swine -erysipelas, Pasteur and Thuillier obtained attenuated 

 virus upon quite another principle. They discovered that by 

 passing the virus through pigeons the virulence was increased, but 

 by passing it through rabbits it was progressively diminished. Thus 

 a virus was obtained from the rabbit, which produced only a mild 

 disease in pigs, and after recovery complete immunity. Similarly 

 in rabies, Pasteur found that passage of the virus through various 

 animals considerably modified its properties. By inoculating a 

 monkey from a rabid dog, and then passing the virus through other 

 monkeys, the virulence was diminished ; but by inoculating a rabbit 

 from the dog, and passing the virus from rabbit to rabbit, the 

 virulence increased. 



In rabies, Pasteur has employed another method of attenuating 

 the virus. The spinal cord of inoculated rabbits is removed with 

 all possible precautions, and portions a few centimetres in length 

 are suspended in flasks in which the air is dried by fragments of 

 potash. By this process the virulence is found to gradually diminish 

 and finally disappear. Animals inoculated with portions of these 

 cords, after suspension for a certain time, are rendered refractory to 

 inoculation with virulent cords. Having rendered dogs, which had 

 been previously bitten, free from the svipervention of symptoms of 

 hydrophobia by means of protective inoculation, Pasteur proceeded 



