346 AGRICULTURAL BACTERIOLOGY. 



was evident that this end could be reached only by weakening 

 the pathogenic powers of the bacilli. After continued experi- 

 menting he finally accomplished his purpose by cultivating 

 the bacilli at a temperature somewhat above that at which 

 they make their best growth. By the use of a temperature of 

 1 08 F. he could cultivate the bacilli, but at this temperature 

 they lost some of their virulence and did not form spores. By 

 continued cultivation at this temperature he obtained cultures 

 which were so weak as to be unable to produce a fatal disease 

 even in susceptible animals. 



After reaching this result Pasteur, by an ever-memorable 

 public experiment, demonstrated to the world the possibility 

 of combating infectious diseases by the use of what are now 

 known as weakened cultures. He inoculated half of a lot of 

 fifty susceptible animals, including cattle and sheep, with his 

 weakened virus. The animals were slightly indisposed, but 

 suffered no evil consequences. In a few days he inoculated 

 them with a second, stronger culture, with a like harmless re- 

 sult. Having thus prepared these test animals he summoned 

 to a public experiment an assemblage of noted men in Paris 

 and, in the presence of the whole, inoculated all of the fifty 

 animals with the strong infectious material taken from an 

 animal dead from the disease. Two days later the company 

 assembled again to find all of the unprotected animals either 

 dead or dying from a violent case of anthrax, while of the 

 protected animals not a single one showed the slightest evil 

 result of the inoculation. A more successful experiment has 

 hardly ever been recorded. 



The announcement of this discovery flew rapidly over the 

 world, and there was at once a great demand for this anthrax 

 vaccine from countries especially affected with the disc-asr. 

 Since that date these weakened anthrax cultures have been 

 made in large quantities and sent all over the world and have 

 been used very extensively. In countries where the disease 



