134 
Journal of Agricultural Research 
Vol. XXVIII, No. 2 
“the larval intestine, which up to this time has been a blind sac, is connected with 
the end gut, allowing defecation to take place. There is then two days of quies¬ 
cence, during which the larva extends in the cell and lies motionless, while internal 
changes preparatory to metamorphosis occur (figs. 3 and 4). These changes (7) 
consist of the almost complete histolysis of the fat body of the larva in order to 
furnish nutriment for the formation of imaginal tissues. This is made possible 
by the physiological and morphological changes occurring 
in this stage of the development of the larva. Extended 
investigations have been made of these physiological and 
morphological changes, but they need not be summarized 
further here, since the present work has been solely of a 
biochemical character. It is noticeable, however, that the 
intestines of mature larvae even for a short time after cap¬ 
ping are full of material colored by the pollen content, 
while the intestines of the prepupae, after they have 
extended in the cell, are colorless. 
It is during the latter two-day prepupal period that 
according to Maassen {28) the invasion of the fat body by 
Bacillus larvae occurs and that according to White {55) 
the majority of the brood dies in American foulbrood. 
In European foulbrood, on the contrary, the majority 
of the larvae in typical cases of this disease die before 
sealing and after reaching an age of 31 to 4 days from 
the time of hatching of the egg {56) (fig. 5). In certain 
abnormal cases in European foulbrood death may occur after capping {46), 
but this almost always occurs during the first two days of the prepupal stage, 
when the larva in most cases is still moving about in the cell, usually causing 
a gross appearance quite different from that of brood 
dead of American foulbrood. 
PRELIMINARY EXPERIMENTS 
While studying the bacterial flora associated with the 
early stages of European foulbrood in the larval intestine 
certain results were obtained which suggested a possible 
explanation of the delayed development in American 
foulbrood. Until death takes place in European foulbrood 
the growth of the organism causing the disease and certain 
secondary associated forms occur only within the intes¬ 
tine {52); that is, within the peritrophic membrane, but 
not in actual contact with living tissues of the larva. It 
is only after death that the secondary invaders, particu¬ 
larly Bacillus alvei , invade the body tissues (45). 
Another important distinction which must be consid¬ 
ered is that the feeding of the larva is not the same 
throughout larval life. Von Planta {40) has shown 
that for the first part of the feeding period one type of 
food is used by the larva and that at a later stage a food different in chemical 
and physical composition is provided. Young larvae receive a food for a time 
after hatching that is much richer in fat and albuminous material but lower 
in sugar content than that fed to older larvae. The food of the older larvae, 
which is known to consist mainly of honey or nectar and pollen, is much 
higher m sugar content, while there is a considerable decrease in fat and 
albuminous material. The sugar in the food of the older larvae, particularly 
Fig. 3.-—Healthy prepupa 
approximately 8 days old, 
having reached the quies¬ 
cent stage. This is the 
age at which the majority 
of larvae die from Ameri¬ 
can foulbrood. End view. 
(White (66)) 
