MICROBIAL DISEASES OF INSECTS 927 



alive. The length of time that a developing bee is sick of European 

 foul brood is variable. In general, the three days just preceding the 

 time when a larva would ordinarily be capped, is the most favorable 

 period for making a diagnosis from the gross examination alone. 

 Healthy larvae at a certain age when slightly magnified show a 

 peristalsis-like motion of their bodies, but larvae of this same age 

 when sick frequently exhibit a marked peristalsis which can easily be 

 seen with the unaided eye. Diseased larvae may show a yellowish 

 tint or appear transparent instead of the glistening white or bluish 

 white of healthy larvae. 



Another symptom often serves for diagnosis. In a healthy larva a 

 pollen-colored mass is frequently plainly seen through the transparent 

 area along the dorsal median line. If this intestinal mass appears 

 white or yellowish white, the presence of European foul brood is al- 

 most certain. This may be often more plainly observed if the larva 

 is removed from the cell with forceps. 



European foul brood may be positively diagnosed in living larvae 

 of a favorable age and condition by the following method : Remove the 

 larva to be tested from the cell and place it upon glass, preferably with 

 a dark background; with a dissecting needle in each hand and with 

 their points near together, pierce with both needles so as to tear the 

 body wall crosswise, and continue to separate the two portions of the 

 larva. If the larva is diseased, and one is successful, it will be found 

 that the intestinal content will be stripped from and pulled out of the 

 posterior and blind end of the canal. The intestinal content of healthy 

 living larvae cannot be removed in this way. The force which is ap- 

 plied in pulling the mass from the intestine frequently causes the typ- 

 ical transparent, mucus-like substance surrounding the central mass to 

 stretch and the enclosed whitish substance to break into segments; 

 this appearance is very characteristic. 



If the disease is more advanced, a portion of the intestinal content 

 may flow out in the form of a sac, the wall of which is very easily bro- 

 ken. When broken the content of this sac-like structure will flow out 

 as a rather thin whitish or yellowish white fluid containing small whitish 

 granules that vary in size. If the disease is far advanced and the larva 

 probably dead, the enveloping substance of the intestinal content is 

 so easily broken that often only the whitish or yellowish-white fluid 

 flows from the ruptured wall of the larva. 



