EUROPEAN FOULBROOD. 



17 



same, were similar to those used in the other studies. The method 

 of making the inoculations was also similar. The colonies were, there- 

 fore, in the open and the bees had free access of flight. The same pre- 

 cautions taken to minimize robbing, swarming, absconding, and drift- 

 ing of bees were observed in the experiments with this disease as with 

 the other diseases. All hives which had housed European foulbrood 

 colonies were flamed before they were used again to be certain that 

 there would be no infection from such a source. Whether the queens 

 used had been in diseased colonies need not give one any concern. 

 Further reference to the technique followed in the present studies will 

 be made as the experiments are discussed. 



THERMAL DEATH POINT OF BACILLUS PLUTON 



The result of the experiments recorded by the writer in an earlier 

 paper (16) shows that when suspended in water the thermal death 

 point of Bacillus pluton is approximately 63° C, the period of ap- 

 plication being 10 minutes. Further experiments have been con- 

 ducted in which the organism was suspended in honey and heated. 

 After being heated, healthy larvae are inoculated by feeding, using 

 the direct or pipette method. Table I summarizes the experiments 

 made: 



Table I. — Resistance to heat of Bacillus pluton suspended in honey 



The results given in the foregoing table show that the thermal 

 death point of Bacillus pluton suspended in honey is approximately 

 79° C, maintained for 10 minutes. 



RESISTANCE OF BACILLUS PLUTON TO DRYING 



In conducting experiments relative to the effect of drying on 

 Bacillus pluton the stomach contents (PI. VIII) of larvae sick or 

 recently dead of European foulbrood are spread in a thin layer in 

 Petri dishes or on slides. From time to time after the films are made 

 healthy larvae are inoculated by feeding a suspension of the drying 

 larval material suspended in a weak sirup solution. When no in- 

 132817°— 20— BuU. 810 3 



