288 MICRO-ORGANISMS AND DISEASE [chap. 



and Greenfield ^ maintain, that continued transference 

 weakens and uhimately destroys the action of the bacilli ; 

 as long as the cultures remain pure, not contaminated and 

 finally suppressed by accidental innocuous bacilli, the 

 anthrax-bacilli retain their virulence. 



Cultures of the blood-bacilli at 20° to 38° C. in neutral 

 broth, during the first or second week, are virulent to mice, 

 guinea-pigs, and rabbits ; but after that they lose their 

 power on mice, provided the growth takes place only in the 

 depth and no spores are formed ; but they retain it as 

 regards guinea-pigs and rabbits, as long as they contain good 

 bacilli at all."^ But fresh cultures made of such bacilli 

 invariably produce a growth which is fatal to all rodents 

 during the first or second week. 



The first observations that bacillus anthracis can become 

 attenuated in its action without losing its morphological and 

 biological characters were recorded by Toussaint, who 

 found that heating anthrax blood up to 55° C. for a few 

 minutes incapacitates such blood from producing anthrax on 

 inoculation. Chauveau then found that the same attenua- 

 tion and destruction of virulence occur when the virulent 

 bacillus anthracis, e.g. the blood, is subjected to the action of 

 5 per cent, carbolic acid for a few minutes. Pasteur was 

 the first who showed that when bacillus anthracis is culti- 

 vated in broth at high temperature (42*5" C.) it gradually 

 loses its full virulence, and when such cultures are inoculated 

 into sheep and cattle a mild and transitory form of anthrax 

 is produced ; animals so treated withstand successfully the 

 further inoculation of virulent materials, and are therefore 

 protected by the inoculation with the attenuated cultures. 



1 Proceedings of the Royal Society, June 17, 1880. 

 Klein, Reports of the Medical Officer of the Local Government Board 

 1881. 



