134 



Journal of Agricultural Research voi. xxvni, No. 2 



Fig. 3.— Healthy prepupa 

 approximately 8 days old, 

 having reached the quies- 

 cent stage. This is the 

 age at which the majority 

 of larvSD die from Ameri- 

 can foulbrood. End view. 

 (White (55)) 



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 

 change.s 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 

 Tn 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 larvse 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 (SS) 

 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 Si 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 

 dead of American foulbrood. 



PEELISnNARY 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 (^5) . 



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 ^'o- ■'•"Healthy prepupa. 

 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 larv* receive a food for a time 

 after hatchmg that is much richer in fat and albuminous material but lower 

 m sugar content than that fed to older larv«. The food of the older larv«, 

 which IS known to consist mainly of honey or nectar and pollen, is much 

 ingher m sugar content, while there is a considerable decrease in fat and 

 albuminous material. The sugar in the food of the older larv^, particulariy 



