AMERICAN" FOULBROOD. 



29 



more heat than the minimum amount that is required as determined 

 by experimental studies. 



RESISTANCE OF AMERICAN FOULBROOD SPORES TO DRYING 



That the American foulbrood spores are able to withstand much 

 drying has long been realized by beekeepers. Scales of American 

 foulbrood obtained in 1907 from colonies in which the disease had 

 been produced through experimental inoculation were stored in 

 the laboratory. Each succeeding year for 9 years tests were made 

 relative to the viability of the spores in this material. In 1916 

 they were still alive and as resistant to heat and as virulent as at 

 any previous time. It is most likely that they would have with- 

 stood the drying at room temperature for a very much longer period 

 than the 9 years. 



RESISTANCE OF AMERICAN FOULBROOD SPORES TO DIRECT SUN- 

 LIGHT 



RESISTANCE OF AMERICAN FOULBROOD SPORES WHEN DRY TO DIRECT SUNLIGHT 



In conducting experiments relative to the resistance possessed 

 by spores of Bacillus larvae, when dry, to the direct rays of the sun, 

 a heavy aqueous suspension is made of the scale material. This 

 is spread in a thin film in Petri dishes and allowed to dry, the amount 

 of disease material in each dish being equal to that in from 3 to 5 

 scales. The dry layer of disease material is then exposed to the 

 direct rays of the sun and after different intervals of time cultures 

 are made to determine whether the spores are viable. Table VIII 

 gives a summary of the experiments made: 



Table VIII. — Resistance of spores of Bacillus larvae when dry to the sun's rays 



Date of experiment. 



1916 



Aug. 31 



Aug. 28 



Sept.5 



Do 



Do 



Sept. 6 



Sept. 28 



Sept. 19 



Sept. 25 



Aug. 23 



Aug. 28 



Sept. 23 



Sept. 25 



Sept. 16 



Do 



Sept. 25 



Period of 

 exposure 



Hours. 



2 



4 



5 



7 



10 



11 



12 



29 



38 



28 



37 



41 



41 



44 



61 



79 



Results as shown from cultures. 



Numerous spores not killed. 

 Many spores not killed. 



Several spores not killed. 

 Few spores not killed. 



Do. 

 Many spores not killed. 

 Several spores not killed. 

 A dozen spores not killed. 

 All spores killed. 



Do.' 

 Do. . 

 Do. 

 Do. 

 Do. 



From Table VIII it will be observed that all of the spores were 

 killed by the direct rays of the sun in from 28 to 41 hours. It is 

 natural to expect that the period required would depend upon the 



