162 
Joumal of Agricultural Research 
Vol. XXVIII, No. 2 
Since it is shown that the concentration of reducing sugars in the larval intes¬ 
tine is usually sufficient to inhibit the growth of Bacillus larvae and thus to prevent 
the manifestation of American foulbrood until after sealing, it is now necessary 
to explain the rare cases in which advanced stages of the disease are seen in 
younger coiled larvae. Such cases are exceedingly rare, except in colonies where 
almost every cell in the brood combs is filled with a dried scale, and where the 
bees have deserted the brood-nest because of this diseased material. There 
can be no doubt that in these cases the earlier manifestation of the disease is 
due to the fact that in such colonies the progressive feeding of the larvae is ser¬ 
iously reduced by the fact that the colony has already been depleted in numbers 
of adult bees. Since there must be a decrease in progressive feeding in such 
cases, the concentration of reducing sugars in the intestine of the larva is obviously 
reduced, causing a condition to exist in these intestinal tracts which no longer 
inhibits the germination and growth of the causative organism. Such rare 
cases of young larvae dead of American foulbrood do not, therefore, disprove 
the theory regarding the time of the development of the disease which has been 
here set forth, but rather serve as further substantiation of it. 
THE COCOON-SPINNING STAGE 
Sealing usually takes place on about the fifth day, at which time apparently 
the intestine contains a maximum amount of unassimilated sugar. After sealing 
occurs and feeding ceases, a different set of factors influence the concentration 
of sugar in the intestinal contents, so that there is a rapid steady decrease from 
this time on. The storage of glycogen and fat, however, continues for a short 
while from the assimilation of reducing sugar. Soon the movements of cocoon 
spinning and the histolysis of tissues make necessary the utilization of energy 
stored in form of glycogen and fat, so that the percentage of these substances 
begins to decrease as the larva loses weight. The emptying of the intestine 
of fecal material during this period also tends to decrease the sugar in the intes¬ 
tine, so that by the time the cocoon is finished, some time between the seventh 
and eighth days, the intestine is empty. The larva has straightened out and 
become quiescent by the eighth day, and all remaining sugar has now been 
assimilated. It is during this period that, as the concentration of sugar decreases, 
a point is reached where the growth of the organism can proceed. This appar¬ 
ently occurs when the sugar concentration in the intestine has decreased to about 
3 to 4 per cent or less, probably not until some time between the sixth and seventh 
days. In the cultural experiments it was found that with 2 per cent or less 
dextrose, vigorous vegetative growth occurs. This vigorous growth requires, 
however, from 24 to 48 hours to develop, depending somewhat on the amount 
of initial inoculum. It is probable, as suggested by observations of Berman 
and Rettger ( 6 ), that this sugar in the food furnishes the energy for vegetative 
growth, while the soluble nitrogenous constituents of the intestinal contents 
furnish material for cell metabolism, until the time when the organisms have 
increased in number sufficiently to cause death and are able to invade the tissues 
of the larva, causing their subsequent decomposition. 
THE QUIESCENT STAGE 
As also is known from long observations of symptoms, the death of the larva 
and invasion of the body tissues do not in the majority of cases take place until 
after the larva has at least reached the age of 8 days and has become quiescent. 
This fact explains the characteristic uniformity of position and appearance of 
the majority of the larvae dead from American foulbrood (figs. 7, 8, and 9). 
There are occasional cases in which death is still further delayed for some reason 
