22 



BULLETIN 809, U. S. DEPARTMEN'T OF AGRICULTURE. 



The bees from diseased colonies may be used again in certain well- 

 selected cases by transferring them to another hive which may be 

 supplied with comb from healthy colonies or with foundation strips 

 or full sheets. To insure that no infection is present a colony treated 

 in this way should be under observation for a con- 

 siderable period after brood rearing has begun in it 

 before it is used again. 



Further reference to the technique used in these 

 studies will be made as the experiments are recorded. 



THERMAL DEATH POINT OF AMERICAN FOULBROOD 

 SPORES 



In an earlier paper (24) the results from preliminary 

 experiments were given which indicate the amount of 

 heating that is necessary to destroy the spores of 

 American foulbrood when they are suspended in water. 

 The importance of heat as a means for the destruction 

 of these spores in practical apiculture is so great that 

 a further development of the subject during these 

 investigations seemed justifiable. 



RESISTANCE OP AMERICAN FOULBROOD SUSPENDED IN WATER 

 TO HEATING 



In preparing the spore material for heating a much 

 diluted aqueous suspension of the disease material is 

 drawn into capsules (fig. 8) made from glass tubing 

 of small bore. After being sealed in a flame they are 

 immersed in a water bath having a temperature and 

 for the period desired in the heating.^ Cultures then 

 are made using a loopful of the suspension from the 

 capsule and brood-filtrate-egg-yolk-suspension agar. 



The results of the experiments given in the following 

 table indicate the approximate amount of heating that 

 is necessary for the destruction of the spores suspended 

 in water. 



Fig. 8.— Capsule used 

 in determining the 

 thermal death 

 point of spores. 



Table I. — Preliminary experiments indicating the thermal death point of the spores oj 



Bacillus larvae suspended in water ^ 



First Set of Experiments. Disease Material Received from Americ* 



Temperature. 



Period of 

 heating. 



Results as shown by cultures, 

 October, 1913. 



"C. 



°F. 



Minutes. 

















Numerous spores alive (check). 



90 



194 



20 



Many spores not killed. 



94 



201 



10 



One spore not killed. 



96 



205 



10 



All sporse killed. 



97 



207 



10 



Do. 



98 



208 



10 



Do. 



99 



210 



10 



Do. 



100 



212 



5 



Do. 



100 



212 



10 



Do. 



> About two minutes are allowed for the suspension within the capsule to reach the temperature of the 

 water outside before time is reckoned. 

 * Fractions are omitted in this paper, the nearest whole number being given. , 



