84 KOPINESS IN WATTLE BARK IXIXSIOXS, 



Cultural Cluiructers. 

 BACTERiUil A, witb phases Al ami A'J. A2a. 

 Morpholo(jij.—A. Gram-negative, motile, short rod with rouudod ends. It 

 appears generally as a rod 0.5 X 1/^j but varies from an apparent coccus to 

 rods up to 2/i in leng-th. Spores were never observed. The flagella are long 

 and vary in number. They are frequently single, and polar, but more often they 

 are peritrichous. Up to five have been observed. 



Nutrient ac/ar stroke.— X raised, glistening, .canary-coloured growth of loose 

 consistency. The cohesive phase A2 grows as a dry rough expansion. 



Nutrient agar colonies.— Xiter a day's incubation at 28° there is little dis- 

 tinction between the phases beyond the tints under the microscope. Al is yel- 

 lowish, A2 is gTey, and all phases are either homogeneous or have a finely granu- 

 lar centre. Differences are readily seen on the second day, when Al is circular, 

 slightly raised and yellowish, while A2 and A2a are milky white and dome- 

 shaped. A2a maintains the dome shape, bvit A2 has developed or will develop 

 a more or less flattened and corrugated base, so that the whole colony has a 

 nipple-shape. In consistency Al is quite loose, A2 and A2a are ropy or tough, 

 and adhere firmly to the agar from which the colony has to be dug away. A2a 

 is more ropy than A2. Microscopically, Al is canary-coloured, A2 and A2a 

 are smoke-coloured or gi-ey. Al has a granular centre witTi homogeneous outer 

 portion. A ring of egg-shaped granules is frequently seen around the centre 

 among the smaller granules which become finer and ultimately vanish in the 

 homogeneous portion. The granulation may be replaced by a stippling due to 

 'the presence of small clusters of crystals of triple phosphate. In old plates, 

 four or five days, the agar becomes studded with comparatively large aggregates 

 of the same crystals. A2a is round, has a dark centre and a cog-wheel struc- 

 lure at the margin. In some cases the centre is lighter, and a rosette structure 

 can be maae out. A marginal ring shows protrusions which alternate with tlie 

 points of the rosette giving rise to the cog-wheel appearance. 



A2 is not rounded or circular like A2a, but is more or less roughly dentate. 

 There are usually from five to seven lobes, more or less roughly pointed, and 

 the rough points consist of frog-s]iawn-like masses of gi-anules. The internal 

 stnicture is not visible, but there is an occasional suggestion of a rosette or 

 radial structure. 



Divergences from these phases have been noted as transition forms. The 

 main difference between Al and A2 is in the colour, the difference between a 

 canary colour and a smoke tint. The yellow transition colonies range from the 

 more or less pitted forms of the stippled or granular colonies of Al to those in 

 which the wliole colony is gTanular with the grannies radiating to the edge and 

 becoming more and more coarsely granular as tiie margin is approached. The 

 smoke-coloured transition colonies show a fibrous structure, the coarse f.bres 

 stretching from a dark centre to near the margin. Some colonies have been 

 seen with this fibrous striicture at one side and the A2 structure at the other. 



The difference in microscopical structip-r is closely associated with tiie flat, 

 dome or nipiilc-shaited macroscopical structure of the colony. 



"Wlien the bacteria have been quiescent for some time, as, for example, 

 when they have been existing iipon agar or in brotli for a month or two without 

 transfer, these differences may not be noted. Raised, flat-topped colonies may 

 form, and these do not show any characteristic markings. 



Ntdrient-gelatin stnh. — Tn three days. Al showed a filiform canal and sunken 

 nail-head. In five days there was a liiiuefied saccate area at the top of tlie canal. 



