VI FURTHER CHARACTERS OF THE BACILLUS 53 



five minutes, and then incubated, it is found to remain 

 free of any growth — that is, to remain sterile ; while 

 a culture tube not exposed to this temperature, on 

 incubation produces good and normal growth. 



Whatever the age of a culture, and whatever the 

 medium in which the bacilli have been growing, a 

 temperature of 60° C, acting for five minutes, kills 

 all life of the bacilli of the grouse 'disease. This fact 

 is, so far as our present knowledge goes, sufficient to 

 justify us in concluding that in those cultures no spores 

 have been formed. 



I have made experiments with regard to the pos- 

 sibility of attenuating the virulence of the bacilli by 

 temperatures below the killing point, viz. below 60° C, 

 in order to obtain easily procurable definite materials 

 by which, on inoculation, owing to the decreased 

 virulence, a slight transitory ailment could be pro- 

 duced which would protect against a second fatal 

 infection ; for I had already ascertained, as mentioned 

 on a former page, that niice, after inoculation with 

 attenuated virus (the cultures derived from the blood 

 bacilli of the grouse dead from the autumn disease), 

 and after recovery from the transitory illness, remain 

 refractory to a second inoculation with virulent cul- 

 tures. 



I exposed, therefore, virulent broth cultures to a 

 tempefature of 50° Fahr., five, ten, fifteen, and twenty 



