28 BULLETIN 810, U. S. DEPARTMENT OF AGRICULTURE. 
Observations made during the present studies indicate that queens 
from European foulbrood colonies are not likely to transmit the 
disease when introduced into healthy colonies. The experiences fur- 
ther show, and the facts in general regarding the disease support the 
conclusions, that the infection will not be transmitted by the hands 
or clothing of the beekeeper, or by visitors to the apiary when the 
manipulations ordinarily practiced are followed. Tools and equip- 
ment used about the apiary are not to be feared unless they supply a 
source for robbing. Hives which have housed infected colonies are 
not likely to be a medium for the spread of the disease. 
Robbing of infected colonies is the most fruitful source of infec- 
tion. A colony weakened by disease (p. 5) becomes a prey for other 
bees. Infectious material is carried to other colonies, thereby trans- 
mitting the infection. Manipulations in the apiary, whereby brood 
combs from diseased colonies are placed in healthy ones, are another 
fruitful source for the transmission of the disease. Preliminary 
work? indicates that stored brood combs from European foulbrood 
colonies may transmit the disease after a considerable period. 
The disease, it would seem, might be spread through the medium 
of honey from infected colonies. The danger from this source, how- 
ever, probably has been overestimated at times (p. 23). That pollen 
stored in the comb would serve as a protection to Bacillus pluton, if 
the parasite were lodged with it, has been determined (p. 24). 
DIAGNOSIS 
The diagnosis of European foulbrood offers more difficulty than 
does that of either American foulbrood or sacbrood. It can usually 
be made, however, from the symptoms alone. Inasmuch as these 
symptoms (p. 4) are rather varied, much care should be exercised in 
ciagnosing the disease. 
The appearance of the adult bees does not aid in the diagnosis. 
A weak colony should arouse suspicion. Increased suspicion is jus- 
tified when no other readily discernible cause for the weakness is to 
be observed. The disease may be present, however, in a strong colony. 
Such a case may be one of recent infection or one which late in the 
recovery from the disease has gained in strength. It may be, how- 
ever, a colony which has suffered only a slight attack of the disease. 
The following outstanding gross characters are often sufficient for 
a diagnosis: The dying of the brood before the time for capping (Pls. 
1 Brood combs were removed from European foulbrood colonies in October, 1914, and 
stored in the laboratory. In May, 1915, one frame of brood comb was placed in each of 
two colonies with the result that European foulbrood was produced in both instances. 
When a frame of the comb was placed in the colony in May, 1916, no disease resulted. 
After 6 months the combs were still able to transmit the disease; after 18 months they 
did not. These experiments are not sufficient to justify definite conclusions but are 
suggestive. 
