NOT DESCRIBED IN PREVIOUS SECTIONS. 543. 
robic (Frankel). Does not form spores. The thermal death-point, 
as determined by the writer, is 56° C., the time of exposure being ten 
minutes. In gelatin plate cultures colonies are quickly developed, 
which give to the medium a fluorescent green color; at the end of 
two or three days liquefaction commences around each colony, and 
usually the gelatin is completely liquefied by the fifth day. Before 
liquefaction commences the deep colonies, under a low power, appear 
as spherical, granular masses, with a serrated margin, and have a. 
yellowish-green color; the superficial colonies are quite thin and 
finely granular ; at the centre, where they are thickest, they have a. 
greenish color, which fades out towards the periphery. 
In stab cultures in nutrient gelatin development is most abun- 
dant near the surface, and causes at first liquefaction in the form 
of a shallow funnel; later the liquefied gelatin is separated from 
that which is not liquefied by a horizontal plane, and a viscid, yel- 
lowish-white mass, composed of bacilli, accumulates upon this sur- 
face, which gradually has a lower level as liquefaction progresses ;. 
the transparent, liquefied gelatin above is covered with a delicate, 
yellowish-green film, and the entire medium has a fluorescent green 
color. Upon nutrientagar a rather abundant, moist, greenish-white 
layer is developed, and the medium acquires a bright green-color, 
which subsequently changes to olive green. Upon potato a viscid 
or rather dry, yellowish-green or brown layer is formed, and the 
potato beneath and immediately around the growth has a green color: 
when freely exposed to the air or to the vapors of ammonia. In milk 
the casein is first precipitated and then gradually dissolved, while at 
the same time ammonia is developed. The green pigment is formed 
only in the presence of oxygen; it is soluble in chloroform and may 
be obtained from a pure solution in long, blue needles ; acids change 
the blue color to red, and reducing substances to yellow. According 
to Ledderhose, it is an aromatic compound resembling anthracene, 
and isnot toxic. According to Gessard’s latest researches (1890), two. 
different pigments are produced by this bacillus, one of a fluorescent. 
green and the other—pyocyanin—of a blue color. Cultivated in egg 
albumin the fluorescent green pigment, which changes to brown. 
with time, is alone produced. In bouillon and in media containing 
peptone or gelatin both pigments are formed, and the pyocyanin 
may be obtained separately by dissolving it in chloroform. In an 
alkaline solution of peptone (two per cent) to which five per cent of 
glycerin has been added the blue pigment alone is formed. 
Pathogenesis.—The experiments of Ledderhose, Bouchard, and: 
others show that this bacillus is pathogenic for guinea-pigs and rab-. 
bits. Subcutaneous or intraperitoneal injections of recent cultures— 
