12 THE CAUSE OF EUEOPEAN FOUL BEOOD. 



In living larvae, therefore, in which European foul brood can be 

 diagnosed from gross examination, it is found that bacteria usually 

 accompany Bacillus plutan. This fact made desirable the study of 

 the diseased larvae in still earlier stages of the infection, i. e., during 

 the period of incubation. This was done culturally in part, but prin- 

 cipally by fixing and sectioning the younger larvas from strongly 

 infected experimental colonies. From such sections it was observed 

 that Bacillus pluton was the first invader of the healthy larva^. 



Figure 10 represents schematically the condition in the larvae at 

 an early stage of infection. In this figure fg represents the f oregut ; 

 mg the midgut, and hg the hindgut. At this age of the larvae the 

 posterior end of the midgut is closed, as represented at h. In the 

 same figure, m represents that portion of the intestinal content lying 

 in contact with the wall of the intestine ; /, the central portion of the 

 drawing, represents the food taken at this age; and p represents 

 what seems to be a peritrophic membrane between the enveloping 

 substance, m, and the paplike food substance, /, of the midgut. 



In the groAvth of Bacillus pluton this jiarasite very early takes a 

 position along the peritrophic membrane />, and just central to it 

 (fig. 10). At this early stage of its growth this microorganism pre- 

 sents in general an appearance of being rod shaped with a strong 

 tendenc}' to groAv in cliains. As tlie disease advances and the growth- 

 mass of this organism increases, the central portion of the lumen of 

 the intestine becomes filled by a solid growth which is made up very 

 largely of Bacillus pluton. During this stage of the disease the con- 

 tent can be removed from the posterior blind end of the midgut, as 

 shown in figure 8. The relation of the central growth-mass to the 

 surrounding mucuslike-appearing mass represented in a, 6, and e 

 of figure 8 is well demonstrated microscopically by sectioning these 

 intestinal masses. 



From the studies made thus far it would seem that Bacillus pluton 

 is easily killed b}' heat. 



PROBABLE EXPLANATIOKS OF ERRORS AS TO THE EXCITING CAUSE OF 

 EUROPEAN FOUL BROOD. 



It is quite probable that others at different times have observed this 

 new species. Bacillus pluton., but have failed to differentiate it from 

 l)acteria which were present and which appeared in the cultures 

 made, leading them thus to erroneous statements concerning the dis- 

 ease and its exciting cause. For example. William R. Howard may 

 have seen this organism microscopically in his so-called " black 

 brood," but failed to differentiate it from some bacterium — Bacillus^ 

 milii or Bacillus alrei — which he cultivated on artificial media. 

 Burri may have seen it in the so-called " sour brood " and mistaken it 



