BACILLUS PYOCYANEUS 215 



death, and is characterised by the formation of bubbles of gas in the 

 infected parts. Its characters are described in Chapter XVII. 



Bacillus pyocyaneus. This organism occurs in the form of minute 

 rods 1*5 to 3 jit in length and less than '5 /* in thickness (Fig. 53). 

 Occasionally two or three are found attached end to end. They are 

 actively motile, and do not form spores. They stain readily with the 

 ordinary basic stains, but are decolorised by Gram's method. 



Cultivation. -It grows readily on all the ordinary media at the room 

 temperature, the cultures being distinguished by the formation of a 

 greenish pigment. In puncture cultures in peptone-gelatin a greyish 

 line appears in twenty-four hours, and at its upper part a small cup of 

 liquefaction forms within 



forty-eight hours. At this . 



time a slightly greenish j i 



tint is seen in the super- * % 



*" * 

 * 



r\* 



ficial part of the gelatin. *.V% '* % . * 



The liquefaction extends *C ** i ** ^' ' * Inl^k. 



pretty rapidly, the fluid ^Jl.rf ,> * ** * 



portion being turbid and , <^ ' i ^ 

 showing masses of growth *. * x *3 * * 

 at its lower part. The m \ *,", .^-' *, A 

 green colour becomes more ^^ 

 and more marked, and dif- i 

 fuses through the gelatin. ^ 

 Ultimately liquefaction 

 reaches the wall of the 

 tube. In plate cultures the 



colonies appear as minute i' 



whitish points, those on 

 the surface being the larger. 

 Under a low power of the 

 microscope they have a 



brownish yellow colour and FlG ' 63.-Bacillus pyocyaneus ; young 

 show a nodulated .surface, g^^SS&i^ xl0 00. 

 the superficial colonies being 

 thinner and larger. Lique- 

 faction soon occurs, the colonies on the surface forming shallow cups 

 with small irregular masses of growth at the bottom, the deep colonies 

 small spheres of liquefaction. Around the colonies a greenish tint 

 appears. On agar the growth forms an abundant slimy greyish layer 

 which afterwards becomes greenish, and a bright green colour diffuses 

 through the whole substance of the medium. On potatoes the growth is 

 an abundant reddish-brown layer resembling that of the glanders bacillus, 

 and the potato sometimes shows a greenish discoloration. 



From the cultures there can be extracted by chloroform a coloured 

 body, pyocyanin, which belongs to the aromatic series, and crystallises 

 in the form of long, delicate bluish -green needles. On the addition of 

 a weak acid its colour changes to a red. 



This organism has distinct pathogenic action in certain animals. 

 Subcutaneous injection of small doses in rabbits may produce a local 

 suppuration, but if the dose be large, spreading hsemorrhagic oedema 

 results, which may be attended by septicaemia. Intravenous injection 

 may produce, according to the dose, rapid septicaemia with nephritis, or 

 sometimes a more chronic condition of wasting attended by albuminuria. 



Micrococcus tetragenus. This organism, first described by Gaffky, is 



