54 THE GROUSE DISEASE chap. 



minutes respectively, and then tested their virulence 

 by inoculation on mice and buntings, but no difference 

 in the virulence of the so-heated cultures could be dis- 

 covered, for the animals inoculated with them died in 

 the same way and time as the control animals inocu- 

 lated with the culture previous to the heating. I then 

 tried heating the virulent broth cultures to 55° C. for 

 ten minutes and for twenty minutes respectively. The 

 result was unsatisfactory, since the cultures so heated 

 proved still virulent. I need hardly add that cultures 

 heated to 55° C. for twenty minutes contain the bacilli 

 in a living condition. Sub-cultures made from such 

 heated cultures all yield normal good growths on 

 inoculation. 



In connection with the action of heat on broth 

 cultures, I wish to mention here the following : — 



Broth cultures incubated from two to three days 

 at 35-37° C. contain chemical substances which them- 

 selves are capable of producing the death of mice 

 on inoculation in sufficient quantities, for when such 

 a broth culture is sterilised, i.e. is exposed for five 

 minutes to 60° C, when hereby all the bacilli are 

 killed, and when from such a sterilised broth culture 

 five minims are injected into mice under the skin 

 of the back, the animals die under the same symp- 

 toms and in the same time as the control mice 

 inoculated with the same amounts of the same broth 



