AMERICAN FOULBROOD. 



25 



From Table III it will be noted that there were about 25,000 

 colonies in the check cultures. When a similar suspension was heated 

 only about 4,000 spores remained alive after 1 minute at 100° C, 

 148 after 5 minutes, 44 after 8 minutes, 14 after 10 minutes, and 

 none after 11 minutes. The conclusion is reached, therefore, that 

 the time element is a factor in the destruction of the spores of 

 American foulbrood by heat. 



These results further show that the spores of different samples 

 vary in their resistance to heat. It is interesting to note that by 

 heating the disease material at 100° C. for one minute, more than 

 80 per cent of the spores were killed, and in 5 minutes, more than 

 99 per cent were destroyed. 



In Table IV are summarized results which indicate further the value 

 of the time element in the destruction of the spores by heat. In this 

 instance spore material from 6 different localities was used, the heat- 

 ing being done at 95° C. with the spores suspended in water: 



Table IV. — Effect of the time element when 95° C. is used in heating American foulbrood 



spores 













Source of samples 







Temperature. 





Period of 

 heating. 































Cuba. 



Colo. 



Ohio 4504. 



N. Y. 



Ohio 4519. 



Minn. 



°C. 



°F. 





Minutes. 















95 





203 



12 



— 



_ 



_ 



— 



_ 



_ 



95 





203 



15 



— 



— 



— 



— 



— 



_ 



95 





203 



20 



— 



_ 



_ 



_ 



_ 



+ 



95 





203 



40 



— 



— 



+ 



+ 



+ 



+ 



95 





203 



50 



— 



— 



+ 



+ 



+ 



+ 



95 





203 



60 



+ 



+ 



+ 



+ 



+ 



+ 



From Table IV it will be observed that the spores from all of the 

 six samples studied resisted in an aqueous suspension a temperature 

 of 95° C. for 15 minutes. Spores from the Minnesota sample were 

 destroyed in 20 minutes at 95° C, those from the Ohio and the New 

 York samples in 40 minutes ; and those from the Colorado and Cuban 

 samples in 60 minutes. The time element is shown again to be an 

 important factor in the destruction of American foulbrood spores. 



These results show also, as was shown above, that the spores con- 

 tained in different samples vary as to their thermal death point. 



Other experiments were made showing the resistance of the spores 

 of Bacillus larvae suspended in water to heat. At 93° C. (199° F.) 

 spores from a Minnesota sample were destroyed in one hour, those 

 from a Colorado sample in 1^ hours, while those from the resistant 

 Cuban sample were not all killed in 3 hours. Experiments using 

 Cuban, Colorado, and Pennsylvania samples showed in each instance 

 that numerous spores remained viable after 2 hours' heating at 90° 

 C. (194° F.). 



