xi] BACILLUS: PATHOGENIC FORMS. 159 



cultivation, 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 illness. After this ill- 

 ness has passed off, the animals are protected against viru- 

 lent anthrax. But with reference to this "vaccination," it 

 must be borne in mind that twenty days' cultivation of blood- 

 bacilli at 42 to 43 C. does not always yield attenuated virus, J 

 and also that sheep and cattle not killed by inoculation of 

 attenuated virus produced by Pasteur's method 2 or by other 

 means (see below), although they are protected against viru- 

 lent anthrax, remain so only for a limited time, probably 

 about nine months. 



In all these experiments with the anthrax-bacilli 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 pro- 

 duces death when inoculated into sheep or cattle, after 

 passing through white mice 3 it loses this virulence for sheep 

 and cattle. The blood of white mice dead of anthrax does 

 not kill sheep ; it produces only a transitory illness and the 

 animals are, for a time at least, protected against virulent 

 anthrax. The blood of guinea-pigs dead of anthrax produces 

 illness, sometimes de|ith, in cattle, but as a rule does not kill 

 (Sanderson and Duguid), and the blood of the biscachia of 



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

 1882. 



2 Pasteur thinks that such cultures remain free of spores because of 

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

 out above ; the state nent only holds good so long as the bacilli are 

 prevented from growing on the surface. 



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

 1882. 



