ATTENUATION OF ORGANISMS. 659 



their virulence, according to Chauveau, in the first normal 

 cultivation, and this is also the case where a temperature 

 of 47 C. has been employed; on the other hand, where, 

 in Pasteur's method, a temperature of only 42 to 43 C. is 

 employed, there is as a rule no return of virulence. Thus 

 Koch cultivated completely attenuated anthrax bacilli 

 which had been kept for twenty-nine days at 42 C. for 

 two j'ears under the most favourable conditions without 

 the last cultivations being able even to infect mice ; at 

 the same time, however, the morphological characters of 

 the bacilli and the appearance of the colonies did not show 

 any difference from those of the virulent bacilli. Ac- 

 cording to Pasteur the virulence can be regained if 

 anthrax bacilli attenuated according to his method are in 

 the first place inoculated on a newly-born guinea-pig; 

 this animal succumbs to the infection, and then an 

 animal one day old is inoculated from the first, then an 

 animal two days old from the second, and so on ; and 

 thus ultimately a gradual increase of virulence is obtained, 

 till even adult animals are killed. Koch, however, on 

 repeating this experiment was unable to confirm these 

 results. 



Among other means of attenuating anthrax bacilli we Attenuation 

 may mention the action of chemical substances which bldUiby* 

 are poisonous to bacteria, a method first employed by carbolic acid 

 Toussaint, and later by Chamberland and Eoux. Ac- 

 cording to the latter authors carbolic acid of the strength 

 of 1 to 600 causes complete attenuation of a cultivation 

 kept for twenty-four days at 35 C. ; if examined after 

 twelve days the cultivation still possesses its full virulence. 

 Solutions of bichromate of potash of the strength of 1 B .v chromic 

 to 1700 kill anthrax bacilli ; where the dilution is greater 

 (1 to 2,000 to 1 to 5,000), it only causes such an attenua- 

 tion that sheep are no longer affected by inoculation, 

 while guinea-pigs and rabbits still die. If a 2 percent. By sulphurous 

 solution of sulphurous acid acts for eight to ten days on acid * 

 anthrax spores at a temperature of 35 C., and if the 

 spores are then cultivated on normal nutrient jelly, a 

 growth is obtained which is still able to kill guinea- 

 pigs, but does not kill rabbits. 



