30 



BULLETIN 809, U. S. DEPARTMENT OF AGRICULTURE. 



date and time of exposure and somewhat upon the thickness of the 

 film of disease material exposed. The climatic conditions during 

 August and September, the time of the experiments, were naturally 

 favorable for the destruction of bacteria by sunlight. The expos- 

 ures were made only when the sky was clear, preference being given 

 to the middle portion of the day. 



REISISTANCE OF AMERICAN FOULBROOD SPORES WHEN SUSPENDED IN HONEY TO 



DIRECT SUNLIGHT 



The technique used is as follows : A concentrated aqueous suspen- 

 sion of spore-containing material is added to honey in Petri dishes, 

 each dish receiving the disease material equal to that of from 3 to 5 

 scales. These are exposed to the direct rays of the sun. The tops 

 are used with the dishes to prevent robbing by bees. After different 

 periods of time the contents of a single dish are added to sirup and 

 fed to a colony free from disease. A set of experiments made is 

 summarized in Table IX. 



Table IX. — Spores of American foulbrood in honey exposed to the sun 



Date 

 of exper- 

 iment. 



Period 

 of expo- 

 sure. 



Results of inoculation. 



1916. 

 July 13 

 July 15 



Hours. 

 6 

 13 



Large amount of American foulbrood produced. 

 Moderate amount of disease produced. 



July 26 

 Aug. 25 

 Sept. 1 

 Aug. 10 

 Aug. 18 

 Sept. 14 

 Do. 



Weeks. 

 2 

 4 

 5 

 4 

 5 

 6 

 8 



Scattering cells of diseased brood. 

 Considerable diseased brood. 



Do. 

 No disease produced. 



Do. 



Do. 



Do. 



The data given in Table IX show that the spores of American 

 foulbrood when suspended in honey were destroyed by the direct 

 rays of the sun in from 4 to 6 weeks. As the suspension in each 

 dish contained the disease material of from 3 to 5 scales it is evident 

 from the results obtained that many of the spores must have been 

 destroyed in a comparatively short period. 



It will be readily appreciated that here again the period required 

 for the destruction of the spores will vary greatly with the intensity 

 of the sun's rays to which the honey suspension is subjected. In 

 these preliminary experiments the period of exposure represents the 

 entire time from. the beginning of the exposure to the time of inocu- 

 lation. There were days during the exposure on which the sun 

 shone a great deal, others on which it shone very little, and still 

 others on which it did not shine at all. The comparatively low tem- 

 perature of the honey suspension attained during the exposure to 

 the sun could not have been an important factor in the destruction 

 of the spores. 



