Apr. 12, 1024 



Development of American Foulbrood 



141 



CUANTITATIVE GROWTH IN PLATE CULTUBE8 



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. 



O.S 



/.O AS 2.0 2.S 



PER CSA/r DEXTROSE 



3.0 



Fig. 10. — Average number of colonies per 4-min. loopful of vegetative culture suspension witli varying suga r 



concentration (Table II) 



QUANTJTATIVE 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 poUen, 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 



