13 
On gelatin plates it developed round, bowl-shaped, liquefying colonies, in 
which there was a uniform white turbidity. A dense white deposit occupied 
the centre of the colony, and smaller, opaque, white masses of bacteria lay at 
many points midway between the centre and the circumference. 
Under the microscope the whole colony was found to be granular. The dense 
centre appeared dark brown, the outer zones lighter in colour. Approximately 
midway between the centre and circumference a denser line, broken at intervals, 
corresponded with the deposits noted microscopically. 
On agar plates colonies were round, moist and cream-coloured. Micro- 
scopically they appeared concentrically zoned, with a granular structure. Dense 
masses like a tilted disc were often embedded in the colony near the centre. 
In gelatin stab cultures, liquefaction was fairly rapid. It was at first crateri- 
form but rapidly became infundibuliform. In 6 days liquefaction was complete. 
A whitish sediment and a uniform white turbidity were characteristic. 
On potato luxuriant growth was produced. It was at first yellow and 
shining, with an even contour; later, it became deeper in colour, spreading and 
of a painty consistency. The potato itself was darkened. 
On litmus milk a light pellicle was formed within 24 hours, followed by 
reduction of litmus, and the clotting and digestion of casein, proceeding from 
the surface downward. The clear liquid became pinkish in colour. The clot 
also, which was at first white, later became pink. 
On agar slants, the growth was luxuriant, spreading evenly along the line of 
inoculation. It was raised, cream-coloured, moist and shining, spreading 
gradually over the entire slant. There was a creamy-white deposit in the water 
of condensation. Indol was formed. 
SUMMARY. 
1. Many forms of bacteria occur normally in Mya arenaria, the long-necked 
clam. 
2. Six of these, belonging to the genus Pseudomonas, are capable of causing 
blackening, if supplied with a favourable medium, containing iron or tin. This 
number includes Pseudomonas fluorescens (Fliigge) Migula., Pseudomonas Jaegeri. 
Mig., Pseudomonas liquefaciens (Tataroff. Mig.) var. marina., and two forms 
which, for reasons stated above, have been given the tentative names, Pseudo- 
monas sericea fluorescens and Pseudomonas myae. 
3. All these blackening organisms were facultative anaerobes. 
All liquified gelatin. 
All reduced nitrates to nitrites. 
All formed acid from dextrose, saccharose and glycerin. 
A change of reaction from acid to alkaline was characteristic in sugar 
media, and usually began on the third or fourth day. 
All were motile, gram-negative rods. 
No spores were observed. 
4. Fluorescence was characteristically produced by three of these organisms, 
namely, Ps. fluorescens (Fliigge) Mig., Ps. Jaegeri, and Ps. sericea (Mig.) var. 
13 
