14 THE CAUSE OP EUROPEAN FOUL BROOD, 



all. This increased the suspicion that Bacillus alvei was not the 

 exciting cause of the disorder. 



(3) In 1907 the writer proved that by feeding pure cultures of 

 Bacillus larvce to healthy bees American foul brood could be produced. 

 This fact still further emphasized the doubt that was already enter- 

 tained concerning the possibilities of Bacillus alvei in the etiology of 

 European foul brood. 



(4) By feeding diseased larvae to healthy colonies it was found that 

 European foul brood could be artificially produced, showing that this 

 disease, too, could be produced by feeding, and that the virus was 

 contained in the diseased brood. 



(5) The sick larva* of the disease thus artificially produced were 

 frequently found, when examined, to be free from Bacillus- alvei. 

 This evidence, too, was damaging to the theory that Bacillus alvei is 

 the cause of a brood disease. 



(6) Bacillus alvei in this way was tentatively eliminated from the 

 list of possible exciting causes of European foul brood. In a quite 

 similar manner the other bacteria — Streptococcus apis, Bacillus me- 

 sentericus vulgaris., Bacillus orpheus, and Bacterium eurydice — were 

 likewise eliminated from the list. 



(7) Considerable quantities of filtrate from aqueous suspensions of 

 crushed diseased larva^ were fed to healthy colonies and in no instance 

 was European foul brood produced. This eliminated tentatively the 

 probability of there being an ultramicroscopic virus in European foul 

 brood capable of producing the disease. 



(8) Bacillus pluton, therefore, was the only factor that was not 

 so eliminated from the list of possible exciting causes of the disease 

 and became thus the probable exciting cause of P^uropean foul brood. 



(9) AMien this organism was studied in larva^ in which the disease 

 could be suspected by inspection alone, one or more species of bacteria 

 were sometimes found to be present also. These, when present, how- 

 ever, occurred in relatively small numbers. 



(10) The disease was then studied in a still earlier stage; i. e., 

 before its presence could be detected by gross examination of the 

 larvae. This was done by cultures in part, but principally by fixing 

 and sectioning larvae during the incubation period of the disease. 

 This study demonstrated that in the production of the disease Bacillus 

 pluton was the first invader of the healthy larvae. 



It will be noticed, therefore, that in the determination of the pri- 

 mary exciting cause of European foul brood two objects were accom- 

 plished: (1) All the factors in the list of possible exciting causes of 

 the disease were eliminated except the one organism Bacillus pluton^ 

 and (2) by the study of infected larvae soon after the infection took 

 place, this parasite was found to be the first invader. 



