130 
Journal of Agricultural Research 
Vol. XXVIII, No. 
THE RELATION OF CONTRIBUTING CAUSES TO THE COMPARATIVE 
DEVELOPMENT OF THE TWO SERIOUS BROOD DISEASES OF 
BEES 
In order to understand the basis upon which the consideration of this problem 
has been developed, it is necessary to make a comparative study of certain of 
the characteristics of the two brood diseases, American foulbrood and European 
foulbrood, aside from their etiology. It will be apparent from this study that 
certain contributing causes, although recognized and described, have not been 
further analyzed to any extent, particularly in relation to specific etiology. 
The experimental work of the present investigation is concerned primarily 
with American foulbrood, however, since the causative organism, Bacillus 
larvae , can be isolated and grown in pure culture, while as yet no artificial medium 
suitable for the growth of Bacillus pluton , the cause of European foulbrood, 
has been devised. 
RACE 
It is an accepted fact that in American foulbrood the race er strain of bees 
has little or no relation to the development of or the resistance to the disease. 
This, aside from apparent lack of immunity or resistance of any of the races, 
may be explained partially by the fact that the decomposed material resulting 
from the death of the larvae is of such a nature that the bees can not to any 
extent remove it from the combs after the disease has once become established. 
The dried-down masses (scales) are practically glued to the cell walls. Bacillus 
larvae forms resistant spores which allow the disease to be carried and spread 
almost indefinitely by means of the honey and old scales. 
In European foulbrood, on the contrary, Italian bees seem to have some character¬ 
istic which makes them more resistant or vigorous in combating infection under 
the proper conditions. The results of bacterial decomposition of the diseased 
remains, even at their worst, are such that, if the colony is able to build up or 
is made sufficiently strong in worker bees, they are able to remove these remains, 
thereby removing the infection sufficiently to prevent its further development. 
Bacillus pluton does not form spores and lives only a comparatively short, time 
under unfavorable conditions for growth, as in honey or on long drying. Fur¬ 
thermore, as has been demonstrated by the writer in a previous paper (45), 
this apparent resistance of the Italian bees was observed to be due largely to 
the racial characteristic of removing all foreign materials more promptly from 
the hive than do common black bees or hybrids, rather than to any natural 
resistance or immunity to the disease. 
STRENGTH OF COLONY 
If a colony of bees has been exposed to infection from American foulbrood, 
the strength of th'e colony apparently has no direct relation to the development 
of the disease, except that strong colonies are usually the ones which rob the 
weaker infected colonies, thereby spreading the infection through the apiary. 
As suggested above, European foulbrood attacks primarily the weak colonies 
which have an insufficient force of bees to remove the infected material. Dis¬ 
eased combs from such a colony can be placed in a strong healthy colony of 
Italian bees with no resulting disease. This would be fatal in the case of Ameri¬ 
can foulbrood. 
SEX 
There has been slight mention in the literature of the relation of the sex of the 
bee larvae to the development of disease. Phillips (38) states with regard to 
European foulbrood: “A symptom of greatest importance is the fact that the 
