Apr. 12,1924 
Development of American Foulbrood 
141 
QUANTITATIVE GROWTH IN PLATE CULTURES 
Great difficulty is found in obtaining satisfactory plate cultures. Only two 
series of plate cultures were obtained which could be counted successfully. The 
average number of colonies showed a definite decrease with increased sugar 
concentration, with no growth at 3 per cent or higher. (Table II, fig. 10). 
As stated above, the plate method, with the small amount of initial inoculum 
necessary for accurate counts, is not a satisfactory method for obtaining growth 
of Bacillus larvae under these conditions, although the method may be used for 
obtaining pure cultures. 
From these observations (Table I) it is, therefore, safe to conclude that a con¬ 
centration of reducing sugar of approximately 3 to 4 per cent or more inhibits 
the growth of Bacillus larvae, although slight germination of spores may take 
place at higher sugar concentrations. 
PER CENT DEXTROSE 
Fig. 10.—Average number of colonies per 4-mm. loopful of vegetative culture suspension with varying sugar 
concentration (Table II) 
QUANTITATIVE DETERMINATION OF UNASSIMILATED SUGAR IN 
THE LARVAL INTESTINE AT VARIOUS AGE PERIODS 
In the preliminary experiments it was shown that unassimilated sugar is 
present in the intestinal contents of the actively feeding larva, which apparently 
i s assimilated completely by the time the prepupa has extended in the cell and has 
become quiescent. Since it is demonstrated that a direct relation exists between 
the growth of Bacillus larvae in suitable culture media and its reducing sugar con¬ 
centration, it is now necessary to determine quantitatively the amount of Unas¬ 
similated sugar in the intestine of the feeding larva and in the intestine of the 
prepupa, in order to determine whether reducing sugar concentration has any 
bearing on the time of attack by American foulbrood. 
COMPOSITION OF BROOD FOOD 
The older bee larvae (40) receive a food consisting of a mixture of honey or 
nectar and pollen, rich in sugar, chiefly reducing sugar. This sugar constitutes 
about 45 per cent of the dried substance, or over 13 per cent of the fresh substance. 
The food of younger larvae contains only about 5 per cent of sugar in the fresh 
