28 BULLETIN 809, U. S. DEPARTMENT OF AGRICULTURE. 



Table VII. — American foulbrood spores heated in honey and fed to bees 



Date of inoculation. 



Temperature. 



Period of 

 heating. 



°a 



°F. 



Minutes. 



100 



212 



10 



100 



212 



12 



100 



212 



15 



100 



212 



18 



100 



212 



20 



100 



212 



25 



100 



212 



30 



100 



212 



30 



100 



212 



45 



100 



212 



90 



100 



212 



120 



Results of inoculation. 



1916 



Aug. 25 



Sept. 12 



Do 



Do 



Aug. 25 



Sept. 12 



Aug. 11 



Aug. 25 



Do 



Oct. 11 



Do 



American foulbrood produced. 

 No disease produced. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



It will be noted from Table VII that American foulbrood was 

 produced after the scale material had been heated in honey for 10 

 minutes at 100° C, but was not produced when this temperature 

 was maintained for 12 minutes or longer. The amount of heating 

 required to prevent American foulbrood in the experiments recorded 

 in this table is not as great as might have been expected from an 

 examination of Table VI. The results tend to indicate that the 

 virulence might have been affected somewhat before the spores 

 were killed. Sufficient data to prove the point, however, are yet 

 lacking. 



From the various experiments relating to the thermal death point 

 of American foulbrood spores recorded on the foregoing pages, it 

 will be observed that 100° C. maintained for 10 minutes, with an 

 exception now and then, is sufficient to kill all of the spores when sus- 

 pended in water. It will be observed also that 98° C. applied for 

 10 minutes will do this in many instances and that 95° C. is sufficient 

 in some cases. It is shown, furthermore, that a large majority of 

 the spores are killed at 90° C. in 10 minutes and also that a very 

 large number of them are killed at 100° C. in 1 minute. 



That a difference exists in the thermal death point of American 

 foulbrood spores was expected. A difference is seen in the spores 

 from different samples, in those from different larvae or pupae in the 

 same sample, and indeed in those of the same larvse or pupae. The 

 maximum difference, when expressed in terms of degrees of tem- 

 perature, between the most resistant spores of any two samples 

 among those studied, the temperature being maintained for 10 

 minutes, is approximately 7° C. ; and when expressed in time, the 

 temperature being maintained at 100° C, is approximately 7 minutes. 

 These differences are for the spores suspended in water. Suspended 

 in honey a greater difference is to be expected. That still greater 

 variations exist than those observed in these studies is most certain. 

 To meet such differences the beekeeper has been urged to employ 

 for the destruction of the spores in practical apiculture somewhat 



