10 BULLETIN 810, U. S. DEPARTMENT OF AGRICULTURE. 
BACILLUS PLUTON 
An artificial medium for the cultivation of Bacillus pluton has not 
yet been devised. To accomplish this may or may not be a particu- 
larly difficult task. The media ordinarily used in the laboratory are 
not suitable. Bee-larve agar, brood-filtrate media, egg-yolk-sus- 
pension agar (19), and combinations of these have not thus far 
proved sufficient for the purpose. The species is an unusual one. 
The generic classification has not been determined definitely and this 
may not be possible until the proper condition for the artificial eulti- 
vation of the species has been supplied. 
The morphology of Bacillus pluton is somewhat variable. In very 
early infection its form is that of a short rod in pairs or in chains, or 
possibly of a coccus with the individuals similarly arranged (fig. 1; 
Pl. VII. B). The length is then equal to or somewhat greater than 
: the breadth. In slightly later 
stages of infection the predomi- 
nating form is that of a lancet- 
shaped coceus (fig. 1; Pl VU, 
A). and in late stages this form 
is present almost exclusively. 
The lancet form occurs singly, 
varying greatly in size and hav- 
ing a length which approximates 
twice the width. The length is 
more often less than 1 y than 
greater. The organism colors 
uniformly with the aniline stains, 
stains with iron hematoxylin, and 
is gram-positive. It does not 
form spores. This is evidenced by the microscopic appearance and 
also by the thermal death point of the species. Its resistance to dry- 
ing, disinfectants, and other environments is discussed Jater in the 
present paper. 
Seven rabbits inoculated, six subcutaneously and one intraperi- 
toneally, with a suspension of larve dead of European foulbrood 
proved to be refractory. Only a slight rise of temperature followed 
the inoculations and the weight was not materially affected. Six 
guinea pigs inoculated subcutaneously with similar material proved 
not to be susceptible to infection with the species. Four pigeons 
inoculated in the pectoral muscles and two white rats inoculated sub- 
cutaneously also proved refractory. In none of these inoculated ani- 
mals were there any lesions of particular note produced. 
Growth of Bacillus pluton in the infected larva begins close to the 
surface of the peritrophic membrane (Pl. VII, I) in contact with the 
food of the larva. As growth continues the bacterial mass extends 
toward the center of the lumen of the peritrophic sac (Pl. VII, K), 
72) 
Fie. 1—Bacillus pluton. 
