8 BULLETIN 671, U. S. DEPARTMENT OF AGRICULTURE. 



When a few colonies are present there is seen, under low magnifica- 

 tion, a granular center for each colony surrounded by numerous 

 smaller but similar growths. There is little chance for error in the 

 identification of B. alvei, assuming that the gross characters of the 

 suspected material cultured had suggested European foulbrood and 

 that the microscopic examination of the material had suggested the 

 organism. 



Cultures should be incubated until the second day in making a 

 diagnosis of suspected European foulbrood material, since spores of 

 B. alvei are not produced in abundance until that time. Two days, 

 then, is the minimum time in which a report can be rendered on this 

 disease. B. vulgatus, B. mesentericus, and B. orpheus may be recog- 

 nized, when present, by their morphology and cultural character- 

 istics (McCray, 1917). 



AMERICAN FOULBROOD. 



American foulbrood is an infectious disease of the brood of bees 

 caused by Bacillus larvae (White, 1907). 



GEOSS CHAEACTEES. 



(a) The caps and regularity of the brood,. — A large amount of the 

 affected brood is capped, and many of the caps may be sunken and 

 many perforated. The coloration, the sunken and perforated caps, 

 and the irregularity produced by the capped and uncapped cells 

 present quite a characteristic appearance (PL I, fig. 2). 



(b) Proportion of affected brood. — The proportion of affected to 

 healthy brood in American foulbrood is, as a rule, high, although 

 specimens secured early in the attack may show a considerable pro- 

 portion of unaffected brood. 



(c) Position of the larvce within the cell. — Inasmuch as most of 

 the larvae in American foulbrood die after the time of capping, the 

 position of the larvae is that of extension along the floor of the cell. 

 But the dead larvae quickly lose their form and symmetry, so that a 

 dark, shapeless mass soon occupies the lower portion and bottom of 

 the cell. 



(d) Age of the affected larvce. — The usual age at which the larvae 

 are found dead of American foulbrood is just after the time of seal- 

 ing. This fact is of importance in considering the size of the scale 

 and its position within the cell. Rarely is young unsealed brood 

 found affected in this disease. 



(e) Color. — Most of the dead larvae when received for diagnosis 

 will be of a dark chocolate color. Only rarely are larvae of the lighter 

 shades of brown seen. The late stages of decay are very dark brown. 



(/) Consistency. — The consistency of the affected larvae is char- 

 acteristic and pathognomonic. The larvae are strikingly viscid, so 



