EUROPEAN FOULBROOD. 9 
For a decade and a half following the observation the belief was 
quite general that this bacterium was the exciting cause of a bee dis- 
ease. The view was then seriously challenged. In 1906 the only 
positive conclusion in regard to the relation between European foul- 
brood and Bacillus alvei that could be drawn by the writer (13) was 
that this species occurs in brood dead of the disease. 
William R. Howard (6), of Texas, after a brief study of the dis- 
ease reported in 1900 the presence of an organism which he called 
Bacillus millii. He cultivated the species apparently with ease. In 
1904 Bahr (1) in Denmark found a small oval bacterium in a brood 
disease in which larvee dying in uncapped cells are yellowish in color 
and not ropy in consistency. Burri (8) in 1906 encountered in his 
studies on the brood diseases a small bacterium which he referred to 
as guntheri-forms. The species was cultured and compared with 
Bacterium guntheri and found to be somewhat different. In 1907 
Maassen (7) obtained from brood material cultures of a species 
which he named Streptococcus apis. White (14) in 1908 reported 
the presence of a small organism in European foulbrood which had 
refused to grow on artificial media. The species was not the one, 
therefore, with which the investigators just referred to had worked. 
That this organism might be the exciting cause of the disease was 
noted. Pending more information regarding it, the species was not 
given a name but was referred to as bacillus “ Y.” That this species 
bears a direct etiological relation to the disease was demonstrated in 
1912 by the writer (15) and the name Bacillus pluton was then given 
to it. 
As the cultivation of Bacillus pluton on artificial media had not 
been accomplished the conclusion that it is the exciting cause of 
European foulbrood was arrived at by eliminating all other possible 
agencies. The observations furnishing the proof appear in an earlier 
paper (15). By demonstrating Bacillus pluton to be the cause of 
the disease, Bacillus alvei, Streptococcus apis, Bacterium eurydice, 
and Bacillus orpheus, and still other species occasionally encountered, 
were thereby proven to be secondary invaders. 
To eliminate the possibility of a filterable virus in European foul- 
brood 10 colonies were inoculated with filtrates obtained from aque- 
ous suspensions of brood sick and dead of the disease. In six 
instances the Berkefeld N filter was used and in four the Pasteur- 
Chamberland F was employed. In no case was the disease produced. 
Studies recorded in the present paper on the resistance of Bacillus 
pluton to heating, drying, fermentation, and disinfectants show that 
when the virus of the disease is not destroyed this species is still alive. 
This fact is further evidence in support of the conclusion that the 
species Bacillus pluton is the virus of the disease. 
132817°—20—Bull. 810-2 
