6 BULLETIN 671, U. S. DEPARTMENT OF AGRICULTUajii. 



(i) Scales. — Scales are formed by the drying of the affected 

 larvae, and from the foregoing description of the dead brood some 

 conception may be gained as to their form and appearance. Scales 

 of European foulbrood, like most of the affected larvae, are small and 

 lie at the bottom of the cell, from which they can be separated with 

 ease. The color of the scale is in general yellow, gray, or brown, 

 and the cross markings formed by the transverse tracheal branches 

 usually are still in evidence. This is the usual type of scale found 

 in European foulbrood. Occasionally there will be received, how- 

 ever, a sample containing only a few scales, or perhaps a single 

 scale, in marked contrast to the scale just described. These scales 

 are always few in number in a given comb area, are usually dark 

 brown in color, are less easily removed than the small ones, and are 

 not brittle but rubberlike in consistency. 



MICROSCOPIC FINDINGS. 



The appearance of Bacillus pluton, the etiological factor in Eu- 

 ropean foulbrood, in stained preparations usually is sufficiently char- 

 acteristic to render its microscopic identification comparatively cer- 

 tain. Besides Bacillus pluton, the following secondary invaders 

 may be found : Bacillus cdvei, Streptococcus apis, Bacillus vulgatus, 

 Bacillus mesentericus, Bacillus orpheus, and Bacterium eurydice. 

 Without careful observation Bacillus pluton and Streptococcus apis 

 might be confused. Upon careful examination it is found that 

 Bacillus pluton presents considerable variation in size and morphol- 

 ogy in the individual organisms. Some of them occur in the form 

 of cocci, yet the general picture is that of an organism with more 

 or less pointed ends. Thin smears should be made in order to obtain 

 details of morphology. 



It is important to have a true conception of the microscopic appear- 

 ance of BaclUus pluton. The essential facts are the typical mor- 

 phology and the manner of grouping of the individual organisms. 

 The general shape of the group is often more or less circular, although 

 nmnerous groups of more or less irregular form may be observed. 

 Groups of varying shapes and sizes will be noted as successive fields 

 are brought into view. It is the presence of these groups, containing 

 a sufficient number of organisms with the pointed ends described 

 that serves to differentiate Bacillus pluton from Streptococcus apis. 

 Streptococcus apis usually occurs in forms which are sufficiently 

 coccuslike to lead to little or no hesitancy in differentiating it from 

 Bacillus pluton. Forms which are sufficiently pointed to resemble 

 B. pluton do occur, however, and if only a few are present in a field 

 the differentiation of these species is not possible. By making a 

 sufficient number of smears from a sufficient number of larvae, forms 



