8 BULLETIN 810, U. S. DEPARTMENT OF AGRICULTURE. 
tered death among brood which has reached the pupal stage. Adult 
bees are not susceptible to infection. 
Sex.—W orker, drone, and queen larve are all susceptible to in- 
fection with Bacillus pluton and any of these may die of European 
foulbrood. 
Race-——Complete immunity from European foulbrood has not 
been found among the races of bees studied. Experimental work 
recorded in the present paper involved the use of at least five 
colonies of “tested Italians,” two of “tested Carniolans,” and two 
of “tested Caucasians.” For the most part the bees used were “ un- 
tested Italians,” but among the colonies were a few common blacks. 
In all these strains the disease was readily produced through experi- 
mental inoculation. The examination of numerous samples of dis- 
eased brood received from beekeepers throughout the United States 
suggests that all races commonly kept by American beekepeers are 
susceptible to European foulbrood.. The relative immunity of the 
different races has not been demonstrated by the studies. These 
facts, however, do not dispute the observation by practical bee- 
keepers that some strains of bees show a greater colony resistance 
than others. 
Climate-—F rom reports of studies made in Austria by Muck (12), 
in Denmark by Bahr (1), in England by Cheshire and Cheyne (4), 
in Germany by Zander (20), and in Switzerland by Burri (8), it is 
clearly evident that the disease discussed in the present paper occurs 
in these different countries. It has been encountered also in many 
sections of the United States and Canada. This distribution shows 
that the infection can exist under a variety of climatic conditions. 
The practical import of the fact is that the presence of European 
foulbrood in any locality can not be attributed entirely to the climate 
of the region. 
Season.—Beekeepers have observed that European foulbrood oc- 
curs with greatest severity before midsummer rather than later in 
the season. The disease, it has been shown experimentally, can be 
produced, however, at any season of the year at which brood is being 
reared. Its severity at any given season is to be attributed, there- 
fore, to environmental conditions rather than to the difference in 
the susceptibility of larve during the different seasons. 
Food—As in American foulbrood it is found that the cause of the 
disease in the colony is governed very little if at all by the quality 
of food gathered by bees. Indirectly, however, the quantity present 
in the hive or obtainable often does influence its course materially. 
EXCITING CAUSE 
That Bacillus alvet may be present in large numbers in brood dead 
of foulbrood was demonstrated by Cheshire and Cheyne (4) in 1885. 
