June, '34] burnside : bacteria associated with European foulbroou 657 



cultural, and biological transformation, and the old doctrine of fixity of 

 bacterial species is gradually giving way before this evidence. Chief 

 among the investigators in this field is Mellon, whose extensive works 

 have demonstrated that many species of bacteria, when cultured under 

 different environments, produce mutants and variants with greater fre- 

 quency than is commonly supposed. Works of Mellon, Hadly {3), 

 Lohnis and Smith {7, 8), and others strongly indicate the existence of 

 life cycles among bacteria similar to life cycles among the fungi. Mellon 

 {10) has aptly stated what seems to be the situation in the following quo- 

 tation: "Thus the analogy is complete, constituting rather formidable 

 evidence for our contention that biologically bacteria may be properly 

 regarded as fungi which have been telescoped down into a state of exist- 

 ence where their life cycles, although much compressed and often abbre- 

 viated, are still not obliterated." 



In 1928 the writer started observations and experiments on European 

 foulbrood to obtain evidence in support of one or another of the theories 

 regarding the cause of this disease. He repeated experiments of others 

 but sometimes interpreted them differently, and he also performed new 

 experiments. Experimental results were not always so conclusive as 

 might be desired and the significance of observations was not always ap- 

 parent. Observations and experimental results which may aid, directly 

 or indirectly, in arriving at a true conception of the etiology of European 

 foulbrood are reported in this paper. 



Morphology of Bacteria in Affected Brood. — Wide variation was 

 observed in the morphology of bacteria present in sick or dead brood. 

 (Plate 6, A, B, and C.) In recently infected larvae the bacteria were 

 mostly very short rods occurring singly, in pairs, or m short chains. 

 Medium-long rods were sometimes present, but no distinctly pointed 

 cells were found during early infection. As the disease progressed and 

 bacteria increased in number, variability in their morphology increased. 

 Most frequently coccoid cells predominated, but at times moderately long 

 rods were equally numerous. Cells of the B. pluton type (Plate 6, C) 

 originated from the coccoid cells at about the time multiplication of bac- 

 teria was checked by overcrowding. The pointed condition appeared to 

 be an expression of dormancy, since these cells usually occurred singly 

 in coherent masses with rarely any indication of active division. In 

 very late infection pointed cells usually predominated, but among differ- 

 ent larvae and different colonies the proportion ranged from 10 per cent 

 or even less to nearly 100 per cent. In some larvae coccoid cells pre- 

 dominated (Plate 6, A), in others moderately long rods were most 

 numerous (Plate 6, B), and occasionally long, slender, faintly staining 



