24 BULLETIN 804, U. S. DEPARTMENT OF AGRICULTURE 



queen has been removed, the juices of which the workers sucked up 

 with avidity, the final eggs laid will be just at the stage where the dis- 

 ease first appears ; that is, 3 to 4 days after hatching, at the end of a 

 6-day period. Furthermore, even though the nurse bees do not feed 

 to healthy larvae the material that is taken up in cleaning out the 

 cells in varying stages of decomposition, infection, even from scales, 

 may be carried on the feet, mouth parts, and tongue, particularly, 

 as was definitely shown with colony H, since these scales are in- 

 fectious. The period of queenlessness and the consequent house 

 cleaning are absolutely dependent on the strength of the colony. A 

 strong colony cleans up rapidly, particularly after the introduction 

 of the new queen in a cage plugged with candy. A weak colony, on 

 the other hand, has not sufficient bees to clean even after complete 

 introduction of a queen, and the disease so^n appears again. Under 

 average conditions, therefore, it would appear unsafe to allow less 

 than a 10-day period of queenlessness in treatment of European foul- 

 brood. 



MICROSCOPICAL BACTERIOLOGICAL OBSERVATIONS 



A large number of microscopic examinations were made of larvae 

 under various conditions for the positive presence of the characteris- 

 tic groups of Bacillus fluton. These examinations were made mainly 

 as a check on the gross observations of the first appearance of the 

 disease. Cover glass smears were made of crushed larvae, stained 

 with carbol fuchsin and mounted in Canada balsam. These examina- 

 tions were made at regular intervals after the colonies were infected, 

 larvae of all ages being examined. 



It was found in the smears of those larvae showing the first slightly 

 abnormal symptoms that Bacillws pluton was the only organism 

 present. This substantiates White's (12) observations that before the 

 disease could be detected by gross examination, by a histological 

 study of sections of larvae during the period of incubation it was 

 demonstrated that " in the production of the disease Baoillus pluton 

 was the first invader of the healthy larvae." 



As the disease advanced in the various colonies, observations were 

 made of larvae in various stages of decomposition. The bacterial con- 

 tent was found to vary with the change of appearance of the larvae 

 during decomposition. The presence of these secondary invaders 

 easily explains the atypical appearance of certain types of European 

 foulbrood that heretofore have been very confusing to the bee- 

 keeper. 



For a short time after the death of the larva, the color remains a 

 moist, creamy-grayish yellow. This is during the period when Bacil- 

 lus pluton and such occasional secondary invaders as Streptococcus 

 apis or Bacteriwm eurydice and other organisms, which do not form 



