180 INFLAMMATION AND SUPPURATION 



It will be thus seen from this account that the streptococcus 

 pyogenes as described above is the organism most frequently 

 associated with the pathogenic processes, and that short-chained 

 forms are common saprophytes in the human body, although 

 they may be associated with conditions of disease ; these may 

 be subdivided according to their fermentative activity as 

 detailed. And lastly, there is the streptococcus conglomeratus 

 (anginosus), which is specially abundant in the throat in scarlet 

 fever, though it also occurs in other acute catarrhal states. No 

 definite statement can yet be made as to the etiological relation 

 of streptococci to scarlet fever ; we can only say that streptococci 

 are almost invariably present in the fauces, and that to them 

 many of the complications of the disease are due. 



Bacillus coli communis. The microscopic and cultural characters are 

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

 and the bacillus pyogenes f&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 XVI. 



Bacillus pyocyaneus. This organism occurs in the form of minute 

 rods 1'5 to 3 fji. in length and less than '5 At in thickness (Fig. 56). 

 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 tint is seen in the superficial part of the 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 agarthe 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 



