BACILLUS PYOCYANEUS. 151 



visible growth takes place. In bouillon, growth forms 

 numerous minute granules which afterwards fall to the 

 bottom, the deposit, which is usually not very abundant, 

 having a sandy appearance. The appearance in broth, 

 however, presents variations which have been used as an 

 aid to distinguish different species of streptococci. It has 

 been found that those which form the longest chains grow 

 most distinctly in the form of spherical granules, those 

 forming short chains giving rise to a finer deposit. To a 

 variety which forms distinct spherules of minute size the 

 term streptococcus conglomerates has been given. The 

 question as to the existence of varieties of streptococcus 

 pyogenes will be discussed below. 



The microscopic and cultural characters of the bacillus 

 coli communis are described in the chapter on typhoid fever. 



Bacillus Pyocyaneus. This organism occurs in the form of minute 

 rods 1.5 to 2 /A in length and less than .5 /A in thickness. Occasion- 

 ally 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 in 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-gelatine 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 gelatine. 

 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 gelatine. 

 Ultimately liquefaction reaches the wall of the tube. In plate cultures 

 the colonies appear as minute whitish points, those in 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 closely that of the glanders 

 bacillus, and the potato sometimes shows a greenish discoloration. 



