162 Journal of Agricultural Research voi. xxvm, 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 larvse. 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 larvse 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 larvse 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 experunents 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 Herman 

 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 ceU 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 larvse dead from American foulbrood (figs. 7, 8, and 9). 

 There are occasional cases in which death is still further delayed for some reason 



