208 INFLAMMATION AND SUPPURATION 



Bacillus coli communis. The microscopic and cultural characters are 

 described in the chapter on typhoid fever. The bacillus lactis aerogenes 

 and the bacillus pyogenes fo&tidus closely resemble it ; they are either 

 varieties or closely related species. The former is distinguished by 

 producing more abundant gas formation, and by its growth on gelatin, 

 etc., being thicker and whiter than that of the bacillus coli. 



Bacillus aerogenes encapsulatus sometimes invades the tissues before 

 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 ^ in length and less than '5 ft in thickness (Fig. 54). 



Occasionally two or three 



_ ^ are found attached end to 



i ss- ^t , end. They are actively 



v A ^ , . N / motile, and do not form 



* V% V ', * spores. They stain readily 



* ^ . | >V *' % * ' with the ordinary basic 



^ A A 1 fc / * stains, but are decolorised 



" t & ** \ *\ '*' b J Gram's method. 



' * * . ,1$* t .* ,* t ' Cultivation. It grows 



readily on all the ordinary 

 media at the room tem- 

 perature, the cultures being 

 distinguished by the for- 

 mation of a greenish pig- 

 '<V - ment. In puncture cul- 

 * """^ **.& ^- tures in peptone-gelatin a 



; ' greyish line appears in 



. -.*** ^ * twenty-four hours, and at 



i * its upper part a small cup 



* of liquefaction forms with- 



in forty-eight hours. At 

 FIG. 54.-Bacillus pyocyaneus ; young thig time a slightlv green . 



<f* 



gelatin. The liquefaction 



extends pretty rapidly, the fluid portion being turbid and showing 

 masses of growth at its lower part. The green colour becomes more and 

 more marked, and diffuses through the gelatin. Ultimately liquefaction 

 reaches the wall of the tube. In plate cultures the colonies appear as 

 minute whitish points, those on the surface being the larger. Under a 

 low power of the microscope they have a brownish-yellow colour and 

 show a nodulated surface, the superficial colonies being thinner and 

 larger. Liquefaction 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. 



