116 MICRO-ORGANISMS AND DISEASE. [CHAP. 



they contain good bacilli at all. 1 But fresh cultures made of 

 such bacilli invariably produce a growth which is fatal to all 

 rodents during the first or second week. 



Pasteur has stated that blood-bacilli which have become 

 attenuated in virulence by exposure to 42 to 43 C. for 

 twenty days are capable of starting new cultures of attenuated 

 virus. This, I question, for I find that such a culture starts 

 new cultures of virulent bacilli ; in the same way the bacilli 

 of a culture that is only " vaccine " for sheep, when it is 

 inoculated into a guinea-pig kills it with anthrax, and then 

 yields bacilli that are fatal to sheep. 



Blood-bacilli exposed to a temperature of 55 C. or to a 

 solution of \ to 1 per cent, of carbolic acid, lose their virulence 

 (Toussaint). Chauveau found that exposure to a temperature 

 of 52 C. for fifteen minutes, or of 50 C. for twenty minutes, 

 destroys the virulence of the blood-bacilli. Pasteur 2 ascer- 

 tained that by cultivating blood-bacilli in chicken-broth at 

 42 43 C. they lose their virulence after twenty days 1 culti- 

 vation, not as Pasteur thinks owing to the action of oxygen, 

 but owing to the high temperature ; and when such bacilli 

 are injected into sheep and cattle they do not kill though they 

 induce sometimes a slight illne?s. After this illness has 

 passed off, the animals are protected against virulent anthrax. 

 But with reference to this " vaccination," it must be borne 

 in mind that twenty days' cultivation of blood-bacilli at 

 42 43 C. does not always yield attenuated virus, 3 and also 

 that sheep and cattle not killed by inoculation of attenuated 

 virus produced by Pasteur's method 4 or by other means (see 

 below), although they are protected against virulent anthrax, 

 remain so only for a limited time, probably about nine 

 months. 



In all these experiments with the anthrax -bacillus it is 

 necessary to bear in mind that by passing the bacilli through 

 different species of animals they become endowed with 

 different qualities, and that bacilli which are fatal to some 

 are not fatal to all animals. While, for instance, the blood- 

 bacillus of sheep or cattle dead of anthrax invariably produces 

 death when inoculated into sheep or cattle, after passing 



1 Klein, "Reports of the Medical Officer of the Local Government Board, 1881. 



2 Comptes Bendit,*, 1881 ; Transactions of the International Medical Congress 

 in London, 1881," vol. i. 



3 Klein, Reports of the Medical Officer of the Local Government Board, 1882. 



4 Pasteur thinks that such cultures remain free of spores becarse of the tem- 

 perature of 42 43 C. ; but this is not so, as has been pointed out above ; the 

 statement only holds good so long as the bacilli are prevented from growing on 

 the st-rfare. 



