356 BACILLI OF NO KNOWN PATHOGENIC PROPERTIES. 



pass out; the zones gradually spread, and the circle 

 of fine rays constantly becomes greater. In the super- 

 ficial colonies the grey centre, and the surrounding narrow 

 darker zone are enclosed in one which is much broader, 

 finely granular, yellow, and highly refracting, and, 

 towards the outer part, gradually more and more colour- 

 less, with indistinct outlines ; and from the margin of this 

 zone fine, radially arranged, and somewhat convoluted 

 lines run into the gelatine. The gelatine is at the same 

 time liquefied, so that the original colonies soon sink 

 below the surface of the material. In puncture cultiva- 

 tions the growth is less characteristic ; complete liquefac- 

 tion of the gelatine soon occurs with the production of a 

 greenish colour, which becomes more yellow as the 

 cultivations get older. On agar material a whitish 

 deposit is formed at the surface, and the substratum 

 assumes a bright green colour. On potatoes the organ- 

 isms form a yellowish-brown moist layer; if this layer 

 is completely removed, and the exposed portion is acted 

 on for a long time by the air, or for a short time by the 

 vapour of ammonia, the surface of the potato becomes 

 greenish. In sterilised milk the bacilli in the first place 

 cause the formation of greenish-yellow flakes on the 

 surface, they then lead to precipitation of the casein, 

 which they peptonise gradually, with the simultaneous 

 appearance of ammonia. 



Colouring The colouring matter produced by the bacilli has been 



investigated by Fordos and Gessard, and has been 

 called pyocyanin. It is soluble in chloroform, and 

 crystallises from the pure solution in the form of long 

 blue needles ; acids convert the blue into red, reduc- 

 ing substances into yellow. It is apparently closely 

 related to the ptomaines because it is precipitated by 

 chloride of platinum, phosphoric molybdic acid, &c. 

 This organism does not cause suppuration, and is 

 apparently only a harmless inhabitant of wounds. 



