24 



BULLETIN 809, IT. S. DEPARTMENT OF AGRICULTURE. 



Further studies relative to the thermal death point of the spores 

 were made on disease samples received from different localities in the 

 United States. The technique followed is similar to that given 

 on page 22. The results obtained are summarized in Table II: 



Table II. — Variation in thermal death point of American foulbrood spores from differ- 

 ent localities in the United States x 







Period of 

 heating. 



Source of samples. 



Temperature. 



Wash. 



Minn. 



Nebr. 



Ohio. 



111. 



Colo. 



Wis. 



Perm. 

 4529. 



Perm. 



4507. 



Ohio 

 4519. 



Mont. 



°C. 



100 

 100 

 100 

 98 

 95 



°F. 

 212 

 212 

 212 



208 

 203 



Minutes. 



10 



5 



1 



10 

 10 



- 



- 



+ 



+ 



+ 



+ 



+ 

 + 



+ 



+ 

 + 



+ 



+ 

 + 



+ 



+ 

 + 



+ 



+ 

 + 



i The minus sign in Tables II and IV indicates that the spores were not all killed and the plus sign that 

 all of them were killed. 



The results in Table II show that in none of the 11 cases were all 

 of the spores killed in 1 minute at 100° C. ; in 5 of the cases they 

 were all killed in 5 minutes at this temperature while in 6 of them 

 they were not. In two instances out of the 11 they were not killed 

 in 10 minutes at 100° C. They were killed, however, at this tempera- 

 ture in 11 minutes. It will be seen also that in no instance were all 

 of the spores killed at 95° C. in 10 minutes, but in 5 of the 11 cases 

 all of them were killed at 98° C. within the 10 minutes. 



By these results it is shown again that the spores of different 

 samples do vary in their resistance to heat. No conclusion is drawn 

 regarding the cause, environmental or otherwise, for this variation. 



TIME A PACTOE IN THE DESTRUCTION OP AMERICAN POULBROOD SPORES BY HEAT 



Suspensions of scales of American foulbrood in water were heated 

 for different periods at 100° C. In the following table are recorded 

 the results obtained when the spores from the Cuban sample were 

 used : 



Table III. — Period of heating American foulbrood spores a factor when 100° C. is used 



Temperature. 



Period of 

 heating. 



Results as shown by cultures, February, 



1915. 



°C. 



°F. 



Minutes. 







100 



212 







25,000 spores present (estimated). 





100 



212 



1 



4,000 spores not killed (estimated). 





100 



212 



5 



148 spores not killed. 





100 



212 



6 



220 spores not killed. 





100 



212 



7 



248 spores not killed. 





100 



212 



8 



44 spores not killed. 





100 



212 



9 



7 spores not killed. 





100 



212 



10 



14 spores not killed. 





100 



212 



11 



All spores killed. 

 Do. 





100 



212 



12 





100 



212 



13 



Do. 





100 



212 



14 



Do. 





100 



212 



15 



Do. 





