3C2 BACTERIOLOGY. 



anthrax, for example, we adopt the plan of in- 

 oculating the animals first with a weaker then 

 with a stronger virus and testing the immunity 

 thus obtained by inoculation with a fully viru- 

 lent material. It was next discovered that 

 animals which, according to Pasteur, were 

 vaccinated securely against wound anthrax, 

 nevertheless, according to Koch, succumbed to 

 intestinal anthrax, and that therefore artificial 

 immunization does not always protect against 

 natural infection. Quite satisfactory results, 

 however, are obtained in both anthrax and 

 swine-erysipelas, and particularly in the dis- 

 ease of cattle known as symptomatic anthrax 

 in districts in which the diseases in question 

 are very prevalent. In the latter disease a pro- 

 tective inoculation is generally 'made spores 

 weakened by steam being used (Kitt). Accord- 

 ing to the method employed for attenuation the 

 less virulent varieties may be degenerate, not 

 growing well in cultures ; or they may have 

 simply become less parasitic, that is to say, 

 more saprophytic, and grow even more lustily 

 than the parasitic parent form (they may have 

 become, that is to say, varieties or modifications 

 of species,' such as occur for instance in the 

 sweet and bitter almonds, in the hemlocks with 

 or without conine, in the cinnamon trees with 

 or without aromatic bark). 



